US 20080027347 A1
The present invention provides methods for minimally invasive, long term monitoring of a physiological signal (e.g., neural signals) from a patient. In preferred embodiments, neural signals are sampled from the patient with an externally powered, leadless implanted device and are transmitted to an external device for further processing.
1. A method of recording neural signals from a patient, the method comprising:
receiving a wireless signal that interrogates an electronic component of an implanted device that is positioned between the patient's scalp and an outer surface of the skull;
sampling the neural signal of the patient with electrodes coupled to the electronic components of the implanted device; and
substantially continuously transmitting a wireless signal that is encoded with data that is indicative of the sampled neural signal from the implanted device to an external device,
wherein the wireless signal that is encoded with data that is indicative of the sampled neural signal is derived from the wireless signal received.
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10. A method of performing brain activity monitoring with a device that is external to a patient, the method comprising:
generating a wireless signal that is configured to provide power to an implanted device and initiate sampling of a neural signal with the implanted device;
receiving a substantially continuous wireless data signal from the implanted device that is encoded with a sampled neural signal;
processing the received data signal in the device that is external to the patient; and
storing the processed data signal in a memory.
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17. A method of monitoring and recording EEG signals from a patient, the method comprising:
minimally invasively implanting a leadless device between the patient's scalp and skull;
generating a radiofrequency signal in an external device;
receiving the radiofrequency signal with an antenna of the implanted leadless device and using the radiofrequency signal to power up and interrogate components of the implanted device;
sampling an EEG signal with electrodes on the implanted leadless device;
transmitting a return radiofrequency signal substantially continuously from the implanted leadless device, wherein the return radiofrequency signal is encoded with the EEG signal;
receiving the return radiofrequency signal encoded with the EEG signal in the external device;
processing the return radiofrequency signal with the encoded EEG signal in the external device; and
storing the processed return radiofrequency signal in a memory of the external device.
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23. A method of recording neural signals from a patient, the method comprising:
powering electronic components of an implanted device by deriving and storing power from patient-based energy sources;
sampling the neural signal of the patient with electrodes coupled to the electronic components of the implanted device; and
substantially continuously transmitting a wireless signal that is encoded with data that is indicative of the sampled neural signal from the implanted device to a portable external device.
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The present application claims benefit of U.S. Provisional Patent Application Ser. No. 60/805,710, filed Jun. 23, 2006, to Harris et al., entitled “Implantable Ambulatory Brain Monitoring System,” the complete disclosure of which is incorporated herein by reference.
The present invention relates generally to methods for sampling one or more physiological signals from a patient. More specifically, the present invention relates to long term, ambulatory monitoring of one or more neurological signals from a patient using a minimally invasive methods.
Epilepsy is a disorder of the brain characterized by chronic, recurring seizures. Seizures are a result of uncontrolled discharges of electrical activity in the brain. A seizure typically manifests itself as sudden, involuntary, disruptive, and often destructive sensory, motor, and cognitive phenomena. Seizures are frequently associated with physical harm to the body (e.g., tongue biting, limb breakage, and burns), a complete loss of consciousness, and incontinence. A typical seizure, for example, might begin as spontaneous shaking of an arm or leg and progress over seconds or minutes to rhythmic movement of the entire body, loss of consciousness, and voiding of urine or stool.
A single seizure most often does not cause significant morbidity or mortality, but severe or recurring seizures (epilepsy) results in major medical, social, and economic consequences. Epilepsy is most often diagnosed in children and young adults, making the long-term medical and societal burden severe for this population of patients. People with uncontrolled epilepsy are often significantly limited in their ability to work in many industries and usually cannot legally drive an automobile. An uncommon, but potentially lethal form of seizure is called status epilepticus, in which a seizure continues for more than 30 minutes. This continuous seizure activity may lead to permanent brain damage, and can be lethal if untreated.
While the exact cause of epilepsy is often uncertain, epilepsy can result from head trauma (such as from a car accident or a fall), infection (such as meningitis), or from neoplastic, vascular or developmental abnormalities of the brain. Most epilepsy, especially most forms that are resistant to treatment (i.e., refractory), are idiopathic or of unknown causes, and is generally presumed to be an inherited genetic disorder.
While there is no known cure for epilepsy, the primary treatment for these epileptic patients are a program of one or more anti-epileptic drugs or “AEDs.” Chronic usage of anticonvulsant and antiepileptic medications can control seizures in most people. An estimated 70% of patients will respond favorably to their first AED monotherapy and no further medications will be required. However, for the remaining 30% of the patients, their first AED will fail to fully control their seizures and they will be prescribed a second AED—often in addition to the first—even if the first AED does not stop or change a pattern or frequency of the patient's seizures. For those that fail the second AED, a third AED will be tried, and so on. Patients who fail to gain control of their seizures through the use of AEDs are commonly referred to as “medically refractory.”
For those patients with infrequent seizures, the problem is further compounded by the fact that they must remain on the drug for many months before they can discern whether there is any benefit. As a result, physicians are left to prescribe AEDs to these patients without clear and timely data on the efficacy of the medication. Because these drugs are powerful neural suppressants and are associated with undesirable side-effects and sedation, it is important to minimize the use and dosage of these drugs if the patient is not experiencing benefit.
A major challenge for physicians treating epileptic patients is gaining a clear view of the effect of a medication or incremental medications. Presently, the standard metric for determining efficacy of the medication is for the patient or for the patient's caregiver to keep a diary of seizure activity. However, it is well recognized that such self-reporting is often of poor quality because patients often do not realize when they have had a seizure, or fail to accurately record seizures. In addition, patients often have “sub-clinical” seizures where the brain experiences a seizure, but the seizure does not manifest itself clinically, and the patient has no way of making note of such seizures.
Demographic studies have estimated the prevalence of epilepsy at approximately 1% of the population, or roughly 2.9 million individuals in the United States alone. In order to assess possible causes for the seizures and to guide treatment for these epileptic patients, epileptologists (both neurologists and neurosurgeons) typically admit the patient to an epilepsy monitoring unit (“EMU”), where the patient will undergo continuous video-EEG monitoring in an attempt to capture ictal brain activity (“seizure activity”) and interictal brain activity.
During their stay in the EMU, the patients may be purposefully stressed in an attempt to induce seizure activity. For example, the patients are often sleep deprived, and if the patients are on medication, the medications may be decreased or stopped. However, for patients who have infrequent seizures, even in such a stressed state, many of such patients do not have a seizure during their stay in the EMU, and such costly and time consuming in-hospital monitoring provides little or no insight into the patient's condition.
While in-patient video-EEG monitoring is currently the standard of care, improvements are still needed. For example, one drawback that has not been addressed by video-EEG monitoring is the fact that the sleep deprivation and/or a decrease or complete stoppage of the AEDs may cause cluster seizures and/or induce status epilepticus—which may not be reflective of the patient's typical seizures or seizure frequency. Thus, the EEG data that is collected in the EMU may not accurately reflect the patient's condition—which can complicate attempts to diagnose and properly treat the patient.
Consequently, what are needed are methods and systems that are capable of long-term, out-patient monitoring of epileptic patients. It would further be desirable if the long-term monitoring could be processed into appropriate metrics that can quantify the clinical benefit of the medication or other therapies. It would also be desirable to have system that could record seizure activity, to enable the meaningful study of patients with infrequent seizures.
The present invention provides methods and systems for monitoring one or more physiological signals from the patient. In preferred embodiments, the present invention provides minimally-invasive systems that provide for the long-term, ambulatory monitoring of patient's brain activity. The systems of the present invention will typically include one or more implantable devices that are capable of sampling and transmitting a signal that is indicative of the patient's brain activity to a data collection device that is external to the patient's body.
Instead of requiring the patient to stay in an EMU, where the patient's are in an unnatural stressed situation, the systems and methods of the present invention allow for out of hospital monitoring and will allow the patient to go about their lives substantially unimpeded. The ambulatory systems of the present invention provide for substantially continuous sampling of brain wave electrical signals (e.g., electroencephalography or “EEG” and electrocorticogram “ECoG”, which are hereinafter referred to collectively as “EEG”). The ambulatory systems of the present invention are more likely to record the occurrence of a seizure—particularly for patients who have infrequent seizures.
A patient could wear their external data collection device at all times of the day (except while showering, etc.). At the physicians' office, the data from the external data collection device could be uploaded into a physician's computer, which could then automatically analyze the stored EEG data and calculate certain metrics that would provide insight into the patient's condition. For example, such metrics may allow the epileptologist to determine if the patient is epileptic, determine the type of epilepsy and seizures, localize one or more seizure focuses, assess seizure frequency, monitor for sub-clinical seizures, determine the efficacy of treatment, determine the effect of adjustments of the dosage of the AED, determine the effects of adjustments of the type of AED, adjust parameters of electrical stimulation, or the like.
The methods of the present invention typically make use of one or more low power implantable devices for sampling the patient's EEG signal. The implantable devices are in communication with a device that is external to the patient's body. The external device is typically configured to transmit power into the implantable device and to store the EEG signal that is sampled by the implantable device. The implantable device and the external device will be in communication with each other through a wireless communication link. While any number of different wireless communication links may be used, in preferred embodiments the systems of the present invention uses a high-frequency communication link. Such a communication link enables transmission of power into the implantable device and facilitates data transfer to and from the implantable device.
In one aspect, the present invention provides a method of recording neural signals from a patient. The method comprises receiving a wireless signal that interrogates and optionally powers an electronic component of an implanted device that is positioned between the patient's scalp and an outer surface of the skull. The neural signals of the patient are sampled substantially continuously with electrodes coupled to the electronic components of the implanted leadless device. A wireless signal is transmitted that is encoded with data that is indicative of the sampled neural signal from the implanted device to an external device. The wireless signal that is encoded with data that is indicative of the sampled neural signal is derived from the wireless signal received from the external device. The wireless signal can be any type of wireless signal—radiofrequency signal, magnetic signal, optical signal, infrared signal, or the like.
In preferred embodiments, the implanted devices are leadless. Typically, implantation is carried out by accessing a space between at least one layer of the scalp and skull with an introducer and injecting (or otherwise inserting) the leadless device into the space through a lumen of the introducer. Because of the high prevalence of temporal lobe epilepsy, in many embodiments, the leadless devices are positioned over the patient's temporal lobe. Of course, the leadless devices may be implanted in any desired area over the skull.
The sampling of the neural signals is preferably carried out substantially continuously, so as to provide a substantially continuous record of the patient's brain activity. The neural signals may be sampled at any sampling rate, but is typically between about 200 Hz and about 1000 Hz.
The neural signals are typically processed prior to transmitting the wireless signal from the patient's body. Processing may include any conventional or proprietary method, but typically includes performing at least one of amplifying, filtering, analog-to-digital converting, compressing, encrypting, and the like. In some embodiments, the implanted devices may include some or all of a neural signal algorithm. The algorithm may comprise feature extractors and classifiers. As such, the processing may comprises extracting features (e.g., electrical biomarkers) from the neural signals that are indicative of the patient's brain state. Such extracted figures may be encoded in the wireless signal that is transmitted to the external device. In one configuration, the extracted features are indicative of the patient's propensity for a neurological event, such as a seizure, tremor, migraine headache, episode of depression, or the like.
In another aspect, the present invention provides a method of performing brain activity monitoring with a device that is external to a patient. The method comprises generating a wireless signal that is configured to provide power to an implanted device and initiate sampling of a neural signal (e.g., EEG, temperature, concentration of chemicals in the brain, or the like) with the implanted device. A wireless data signal is received from the implanted device that is encoded with a sampled neural signal and the received data signal is processed in the device that is external to the patient. The processed data signal is thereafter stored in a memory.
In preferred embodiments, the implanted device is leadless and is implantable in the patient in a minimally invasive fashion, e.g., between the skull and at least one layer of the patient's scalp.
The wireless signal generated and transmitted to the leadless implanted device is typically a radiofrequency signal, but could also be an optical signal, infrared signal, ultrasonic signal, magnetic signal or the like. The wireless signal transmitted to the implanted device and received back from the implanted device typically has a sampling rate between about 200 Hz and about 1000 Hz. In addition to being encoded with the sampled neural signal, the wireless signal received from the implanted device may include an extracted feature that is indicative or predictive of the patient's brain state. The brain state is typically indicative of the patient's propensity for a neurological event.
Processing the received signal in the external device may include any number of processing steps. Processing may include amplification, filtering, converting, decrypting, uncompressing, etc. For embodiments that are more than just a data collection device, the external device may comprise a portion or all of a neural signal algorithm. In such embodiments, processing comprises running the data signal through the algorithms to extract one or more features from the neural signals and classifying the extracted feature(s) to estimate the patient's brain state. The estimated brain state may be indicative or predictive of the patient's propensity for a neurological event, such as a seizure, tremor, migraine headache, episode of depression, or the like.
The external device will typically include a user interface. The user interface may be used to provide system status indication (such as an output regarding battery strength of the external device and a warning signal when the implanted devices is out of communication range of the external device) and brain state indications (that indicate the patient's different propensities for a neurological event)
In some embodiments, when it is estimated that the patient has an elevated propensity for a seizure, the external device may be configured to generate a control signal that facilitates delivery of a therapy to the patient. The therapy may be electrical stimulation that is delivered by the implanted devices, or the therapy may be delivered by additional implanted devices—such as a deep brain stimulator, spinal cord stimulator, vagus nerve stimulator, cortical stimulator, implanted drug pumps, or the like.
In a further aspect, the present invention provides a method of monitoring and recording EEG signals from a patient. The method comprises minimally invasively implanting a leadless device between the patient's scalp and skull. A radiofrequency signal is generated in an external device and the radiofrequency signal is received with an antenna of the implanted leadless device. The radiofrequency signal is used to power up and interrogate components of the implanted device. An EEG signal is sampled with electrodes on the implanted leadless device and a return radiofrequency signal is transmitted from the implanted leadless device to the external device. The return radiofrequency signal is encoded with the EEG signal. The return radiofrequency signal encoded with the EEG signal is received in the external device and is processed therein. Thereafter, the processed return radiofrequency signal is stored in a memory of the external device.
The external device typically comprises a user interface that provides output communications to the patient implanted with the leadless devices. The user interface may be used to generate an output to the patient that indicates their estimated brain state (e.g., propensity for a seizure). Additionally, the user interface may be used to indicate when the external device is not receiving the return radiofrequency signal from the leadless implanted device. Such a signal may indicate to the patient that the external device is out of communication range or that there is a problem with one of the components of the system.
In some embodiments, the return radiofrequency signal is encrypted or otherwise protected so as to safeguard the patient's privacy.
The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:
Certain specific details are set forth in the following description and figures to provide an understanding of various embodiments of the invention. Certain well-known details, associated electronics and devices are not set forth in the following disclosure to avoid unnecessarily obscuring the various embodiments of the invention. Further, those of ordinary skill in the relevant art will understand that they can practice other embodiments of the invention without one or more of the details described below. Finally, while various processes are described with reference to steps and sequences in the following disclosure, the description is for providing a clear implementation of particular embodiments of the invention, and the steps and sequences of steps should not be taken as required to practice this invention.
The term “condition” is used herein to generally refer to the patient's underlying disease or disorder—such as epilepsy, depression, Parkinson's disease, headache disorder, etc. The term “state” is used herein to generally refer to calculation results or indices that are reflective a categorical approximation of a point (or group of points) along a single or multi-variable state space continuum of the patient's condition. The estimation of the patient's state does not necessarily constitute a complete or comprehensive accounting of the patient's total situation. As used in the context of the present invention, state typically refers to the patient's state within their neurological condition. For example, for a patient suffering from an epilepsy condition, at any point in time the patient may be in a different states along the continuum, such as an ictal state (a state in which a neurological event, such as a seizure, is occurring), a pre-ictal state (which is a neurological state that immediately precedes the ictal state), a pro-ictal state (a state in which the patient has an increased risk of transitioning to the ictal state), an inter-ictal state (a state in between ictal states), a contra-ictal state (a protected state in which the patient has a low risk of transitioning to the ictal state within a calculated or predetermined time period), or the like. A pro-ictal state may transition to either an ictal or inter-ictal state. A pro-ictal state that transitions to an ictal state may also be referred to herein as a “pre-ictal state.”
The estimation and characterization of “state” may be based on one or more patient dependent parameters from the a portion of the patient's body, such as electrical signals from the brain, including but not limited to electroencephalogram signals and electrocorticogram signals “ECoG” or intracranial EEG (referred to herein collectively as EEG”), brain temperature, blood flow in the brain, concentration of AEDs in the brain or blood, changes thereof, etc.). While parameters that are extracted from brain-based signals are preferred, the present invention may also extract parameters from other portions of the body, such as the heart rate, respiratory rate, blood pressure, chemical concentrations, etc.
An “event” is used herein to refer to a specific event in the patient's condition. Examples of such events include transition from one state to another state, e.g., an electrographic onset of seizure, end of seizure, or the like. For conditions other than epilepsy, the event could be an onset of a migraine headache, onset of a depressive episode, a tremor, or the like.
The occurrence of a seizure may be referred to as a number of different things. For example, when a seizure occurs, the patient is considered to have exited a “pre-ictal state” or “pro-ictal state” and has transitioned into the “ictal state”. However, the electrographic onset of the seizure (one event) and/or the clinical onset of the seizure (another event) have also occurred during the transition of states.
A patient's “propensity” for a seizure is a measure of the likelihood of transitioning into the ictal state. The patient's propensity for seizure may be estimated by determining which “state” the patient is currently in. As noted above, the patient is deemed to have an increased propensity for transitioning into the ictal state (e.g., have a seizure) when the patient is determined to be in a pro-ictal state. Likewise, the patient may be deemed to have a low propensity for transitioning into the ictal state when it is determined that the patient is in a contra-ictal state.
The methods, devices and systems of the present invention are useful for long-term, ambulatory sampling and analysis of one or more physiological signals, such as a patient's brain activity. In one preferred embodiment, the system of the present invention may be used to monitor and store one or more substantially continuously sampled EEG signals from the patient, while providing a minimal inconvenience to the patient. Attempts at developing ambulatory monitoring systems in the past have relied on an array of electrodes being placed on the patient's head and scalp with adhesive. Unfortunately, such systems are poorly tolerated by patients and are impractical for the duration of time needed for the accurate evaluation of the patient's EEG and evaluation of the efficacy of the treatment the patients are undergoing. Unlike conventional ambulatory EEG systems, the ambulatory monitoring systems of the present invention typically include one or more devices that are implanted in a minimally invasive fashion in the patient and will be largely unnoticed by a patient as they go about their day-to-day activities. The implantable devices may be in wireless communication with an external device that may be carried by the patient or kept in close proximity to the patient. Consequently, the ambulatory monitoring systems of the present invention are conducive to longer, more effective monitoring of the patient (e.g., one week or longer, one month or longer, two months or longer, three months or longer, six months or longer, one year or longer, etc.).
The methods, devices and systems of the present invention may also find use in an emergency room or neurological intensive care units (ICU). For example, the systems may be used to monitor patients who have complex, potentially life-threatening neurological illnesses or brain injuries. Neuro ICUs may monitor patients who have suffered (or thought to have suffered) a stroke (e.g., cerebral infarction, transient ischemic attacks, intracerebral hemorrhage, aneurismal subarachnoid hemorrhage, arteriovenous malformations, dural sinus thrombosis, etc.), head trauma, spinal cord injury, tumors (e.g., spinal cord metastases, paraneoplastic syndromes), infections (e.g., encephalitis, meningitis, brain abscess), neuromuscular weakness (e.g., Guillain-barre syndrome, myasthenia gravis), eclampsia, neuropleptic malignant syndrome, CNS vasculitis, migraine headaches, or the like.
The neuro-ICUs require the ability to monitor the patient's neurological condition for a long period of time to identify issues and diagnose the patient before permanent neurological damage occurs. Because the systems of the present invention are able to provide real-time monitoring of a patient's EEG and many embodiments have the ability to detect or predict neurological events, such systems will be beneficial to patients and the staff of the ICU to allow the neurologist and support staff to detect and/or prevent complications that may arise from the patient's neurological condition, before the patient's condition deteriorates.
For example, a patient who is suffering from head trauma may be outfitted with a system of the present invention and because the implantable portions are MRI safe, the patient's may still undergo MRI sessions. Furthermore, the systems of the present invention may also be used to continuously monitor a patient's response to a drug therapy while the patient is in the neuro-ICU and when the patient leaves the neuro-ICU.
For epilepsy patients in particular, the monitoring systems of the present invention may be used in conjunction with, or as an alternative to, the in-patient video-EEG monitoring that occurs in the EMU. If used as an alternative to in-patient video-EEG monitoring, in some embodiments it may be desirable to provide one or more video recorders in the patient's home to provide time-synced video recording of the patient as they live with their ambulatory monitoring system. In some embodiments, it may be desirable to provide a patient-mounted video system so as to allow video-monitoring of the patient outside of their home. Such a video system may or may not be in communication with the ambulatory monitoring system of the present invention; but both the video and the monitored EEG signals should be time-synced and analyzed together by the physician to assess the patient's condition and/or efficacy of any therapy that the patient may be undergoing.
The systems and methods of the present invention may incorporate EEG analysis software to estimate and monitor the patient's brain state substantially in real-time. The EEG analysis software may include a safety algorithm, a seizure prediction algorithm and/or a seizure detection algorithm that uses one or more extracted features from the EEG signals (and/or other physiological signals) to estimate the patient's brain state (e.g., predict or detect the onset of a seizure). Additionally, some systems of the present invention may be used to facilitate delivery of a therapy to the patient to prevent the onset of a predicted seizure and/or abort or mitigate a seizure after it has started. Facilitation of the delivery of the therapy may be carried out by outputting a warning or instructions to the patient or automatically delivering a therapy to the patient (e.g., pharmacological, electrical stimulation, etc.). The therapy may be delivered to the patient using the implanted devices that are used to collect the ambulatory signals, or it may be delivered to the patient through a different implanted device. A description of some systems that may be used to delivery a therapy to the patient are described in commonly owned U.S. Pat. Nos. 6,366,813 and 6,819,956, U.S. Patent Application Publication Nos. 2005/0021103 (published Jan. 27, 2005), 2005/0119703 (published Jun. 2, 2005), 2005/0021104 (published Jan. 27, 2005), 2005/0240242 (published Oct. 27, 2005), 2005/0222626 (published Oct. 6, 2005), and U.S. patent application Ser. No. 11/282,317 (filed Nov. 17, 2005), Ser. Nos. 11/321,897, 11/321,898, and 11/322,150 (all filed Dec. 28, 2005), the complete disclosures of which are incorporated herein by reference.
For patients suspected or known to have epilepsy, the systems of the present invention may be used to provide data and other metrics to the patients and physicians that heretofore have not been accurately measurable. For example, the data may be analyzed to (1) determine whether or not the patient has epilepsy, (2) determine the type of epilepsy, (3) determine the types of seizures, (4) localize or lateralize one or more seizure foci, (5) assess baseline seizure statistics and/or change from the baseline seizure statistics (e.g., seizure count, frequency, duration, seizure pattern, etc.) (6) monitor for sub-clinical seizures, assess a baseline frequency of occurrence, and/or change from the baseline occurrence, (7) measure the efficacy of AED treatments, (8) assess the effect of adjustments of the dosage of the AED, (9) determine the effects of adjustments of the type of AED, (10) determine the effect of, and the adjustment to parameters of, electrical stimulation (e.g., vagus nerve stimulation (VNS), deep brain stimulation (DBS), cortical stimulation, etc.), (11) determine “triggers” for the patient's seizures, (12) assess outcomes from surgical procedures, (13) provide immediate biofeedback to the patient, (14) screen patients for determining if they are an appropriate candidate for a seizure advisory system or other neurological monitoring or therapy system, or the like.
The systems of the present invention typically include one or more implantable devices that are in wireless communication with an external data collection device, typically with a high frequency communication link. The implantable devices of the present invention are typically implanted in a minimally invasive fashion beneath at least one layer of the scalp, above the patient's skull/calvarium, and over one or more target area of the patient's brain. As will be described in more detail below, the implantable devices are typically injected underneath the skin/scalp using an introducer, trocar or syringe-like device using local anesthesia. It is contemplated that such a procedure could be completed in 20 to 30 minutes by a physician or neurologist in an out-patient procedure.
The implantable devices are typically used to continuously sample the physiological signals for a desired time period so as to be able to monitor fluctuations of the physiological signal over substantially the entire time period. In alternative embodiments, however, the implantable devices may be used to periodically sample the patient's physiological signals or selectively/aperiodically monitor the patient's physiological signals.
The implantable devices may be permanently or temporarily implanted in the patient. If permanently implanted, the devices may be used for as long as the monitoring is desired, and once the monitoring is completed, because the implanted devices are biocompatible they may remain permanently implanted in the patient without any long term detrimental effects for the patient. However, if it is desired to remove the implanted devices, the devices may be explanted from the patient under local anesthesia. For ease of removal, it may be desirable to tether or otherwise attach a plurality of the implantable devices together (e.g., with a suture or leash) so that a minimal number of incisions are needed to explant the implantable devices.
Exact positioning of the implanted devices will usually depend on the desired type of monitoring. For patients who are being monitored for epilepsy diagnosis, the suspected type of epilepsy may affect the positioning of the implantable devices. For example, if the patient is thought to have temporal lobe epilepsy, a majority of the implantable devices will likely be located over the patient's temporal lobe. Additionally, if the focus of the seizure is known, it may be desirable to place a plurality of implantable devices directly over the focus. However, if the focus has not been localized, a plurality of implantable devices may be spaced over and around the target area of the patient's brain (and one or more implantable devices contralateral to the target area) in an attempt to locate or lateralize the seizure focus.
The number of implantable devices that are implanted in the patient will depend on the number of channels that the physician wants to concurrently monitor in the patient. Typically however, the physician will implant 32 or less, and preferably between about 2 and about 16 implantable devices, and most preferably between about 4 and about 8 implantable devices. Of course, in some instances, it may be desirable to implant more or less, and the present invention is not limited to the aforementioned number of implanted devices.
While the remaining discussion focuses on methods of using the systems and devices of the present invention for ambulatory monitoring of EEG signals of patients and patient populations for the diagnosis of epilepsy and/or evaluation of the efficacy and dosing of the patient's AEDs, it should be appreciated that the present invention is not limited to sampling EEG signals for epilepsy or for monitoring the efficacy of AEDs. For example, the implanted devices may be implanted under the skin of the patient's face, within the muscle of the patient's face, within the skull, above the jaw (e.g., sphenoidal implant that is placed under the skin just above the jaw to monitor the brain activity in the temporal lobes), or any other desired place on the patient's body. Furthermore, in addition to or as an alternative to monitoring EEG signals from the patient, it may be desired to monitor other physiological signals from a patient. For example, the system of the present invention may be used to monitor one or more of a blood pressure, blood oxygenation, temperature of the brain or other portion of the patient, blood flow measurements in the brain or other parts of the body, ECG/EKG, heart rate signals and/or change in heart rate signals, respiratory rate signals and/or change in respiratory rate signals, chemical concentrations of medications, pH in the blood or other portions of the body, other vital signs, other physiological or biochemical parameters of the patient's body, or the like.
Furthermore, the systems of the present invention may be useful for monitoring and assisting in the analysis of treatments for a variety of other neurological conditions, psychiatric conditions, episodic and non-episodic neurological phenomenon, or other non-neurological and non-psychiatric maladies. For example, the present invention may be useful for patients suffering from sleep apnea and other sleep disorders, migraine headaches, depression, Alzheimer's, Parkinson's Disease, eating disorders, dementia, attention deficit disorder, stroke, cardiac disease, diabetes, cancer, or the like. Likewise, the present invention may also be used to assess the symptoms, efficacy of pharmacological and electrical therapy on such disorders.
Referring now to the Figures,
The physician may implant any desired number of devices in the patient. As noted above, in addition to monitoring brain signals, one or more additional implanted devices 12 may be implanted to measure other physiological signals from the patient.
While it may be possible to implant the implantable devices 12 under the skull and in or on the brain, it is preferred to implant the implantable devices 12 in a minimally invasive fashion under at least one layer of the patient's scalp and above the skull. Implantable devices 12 may be implanted between any of the layers of the scalp (sometimes referred to herein as “sub-galeal”). For example, the implantable devices may be positioned between the skin and the connective tissue, between the connective tissue and the epicranial aponeurosis/galea aponeurotica, between the epicranial aponeurosis/galea aponeurotica and the loose aerolar tissue, between the loose aerolar tissue and the pericranium, and/or between the pericranium and the calvarium. In some configurations, it may be useful to implant different implantable devices 12 between different layers of the scalp.
Implantable devices 12 will typically be configured to substantially continuously sample the brain activity of the groups of neurons in the immediate vicinity of the implanted device. In some embodiments, if placed below the skull and in contact with the cortical surface of the brain, the electrodes may be sized to be able to sample activity of a single neuron in the immediate vicinity of the electrode (e.g., a microelectrode). Typically, the implantable device 12 will be interrogated and powered by a signal from the external device to facilitate the substantially continuous sampling of the brain activity signals. Sampling of the brain activity is typically carried out at a rate above about 200 Hz, and preferably between about 200 Hz and about 1000 Hz, and most preferably at about 400 Hz, but it could be higher or lower, depending on the specific condition being monitored, the patient, and other factors. Each sample of the patient's brain activity will typically contain between about 8 bits per sample and about 32 bits per sample, and preferably between about 12 bits per sample and about 16 bits per sample. Thus, if each return communication transmission to the external device includes one EEG sample per transmission, and the sample rate is 400 Hz and there are 16 bits/sample, the data transfer rate from the implantable devices 12 to the external device 14 is at least about 6.4 Kbits/second. If there are 32 implantable devices, the total data transfer rate for the system 10 would be about 205 Kbits/second. In alternative embodiments, it may be desirable to have the implantable devices sample the brain activity of the patient in a non-continuous basis. In such embodiments, the implantable devices 12 may be configured to sample the brain activity signals periodically (e.g., once every 10 seconds) or aperiodically.
Implantable device 12 may comprise a separate memory module for storing the recorded brain activity signals, a unique identification code for the device, algorithms, other programming, or the like.
A patient instrumented with the implanted devices 12 will typically carry a data collection device 14 that is external to the patient's body. The external device 14 would receive and store the signal from the implanted device 12 with the encoded EEG data (or other physiological signals). The external device is typically of a size so as to be portable and carried by the patient in a pocket or bag that is maintained in close proximity to the patient. In alternative embodiments, the device may be configured to be used in a hospital setting and placed alongside a patient's bed. Communication between the data collection device 14 and the implantable device 12 typically takes place through wireless communication. The wireless communication link between implantable device 12 and external device 14 may provide a communication link for transmitting data and/or power. External device 14 may include a control module 16 that communicates with the implanted device through an antenna 18. In the illustrated embodiment, antenna 18 is in the form of a necklace that is in communication range with the implantable devices 12. It should be appreciated however, that the configuration of antenna 18 and control module 16 may be in a variety of other conventional or proprietary forms. For example, in another embodiment control module 16 may be attached around an arm or belt of the patient, integrated into a hat, integrated into a chair or pillow, and/or the antenna may be integrated into control module 16.
In order to facilitate the transmission of power and data, the antenna of the external device and the implantable devices must be in communication range of each other. The frequency used for the wireless communication link has a direct bearing on the communication range. Typically, the communication range is between at least one foot, preferably between about one foot and about twenty feet, and more preferably between about six feet and sixteen feet. As can be appreciated, however, the present invention is not limited to such communication ranges, and larger or smaller communication ranges may be used. For example, if an inductive communication link is used, the communication range will be smaller than the aforementioned range.
In some situations, it may be desirable, to have a wire running from the patient-worn data collection device 14 to an interface (not shown) that could directly link up to the implanted devices 12 that are positioned below the patient's skin. For example, the interface may take the form of a magnetically attached transducer, as with cochlear implants. This could enable power to be continuously delivered to the implanted devices 12 and provide for higher rates of data transmission.
In some configurations, system 10 may include one or more intermediate transponder (not shown) that facilitates data transmission and power transmission between implantable device 12 and external device 14. The intermediate transponder may be implanted in the patient or it may be external to the patient. If implanted, the intermediate transponder will typically be implanted between the implantable device 12 and the expected position of the external device 14 (e.g., in the neck, chest, or head). If external, the transponder may be attached to the patient's skin, positioned on the patient's clothing or other body-worn assembly (e.g., eyeglasses, cellular phone, belt, hat, etc.) or in a device that is positioned adjacent the patient (e.g., a pillow, chair headrest, etc.). The intermediate transponder may be configured to only transmit power, only transmit data, or it may be configured to transmit both data and power. By having such intermediate transponders, the external device 14 may be placed outside of its normal communication range from the implanted devices 12 (e.g., on a patient's belt or in a patient's bag), and still be able to substantially continuously receive data from the implantable device 12 and/or transmit power to the implantable device 12.
Transmission of data and power between implantable device 12 and external device 14 is typically carried out through a radiofrequency link, but may also be carried out through magnetic induction, electromagnetic link, Bluetooth® link, Zigbee link, sonic link, optical link, other types of wireless links, or combinations thereof.
One preferred method 11 of wirelessly transmitting data and power is carried out with a radiofrequency link, similar to the link used with radiofrequency identification (RFID) tags. As illustrated in
At step 17 the same RF signal interrogates the energized implantable device 12 to allow the implantable device to sample the desired physiological signal from the patient (such as an EEG signal). At step 19, the implantable device samples the instantaneous EEG signal (or other physiological signal) from the patient.
At step 21, the implantable device 12 then communicates a return RF signal to the external device 14 that is encoded with data that is indicative of the sampled EEG signal. Typically, the return RF signal is a based on the RF signal generated by the external device and includes detectable modifications which indicate the sampled EEG signal. For example, the return signal is typically a backscattering of the RF signal from the external device with the detectable modifications that indicate the sampled EEG signal. Advantageously, such backscattering does not require generation of a separate radiating signal and would not require an internal power source. The return RF signals may also include the identification code of the implanted device so as to identify which device the data is coming from. At step 23, the return RF signal emitted by the internal device 12 is received by the antenna 18, and the RF signal is decoded to extract the sampled EEG signal. The sampled EEG signal may thereafter be stored in a memory of the external device 14. For embodiments in which the method is used to collect data, such data will be stored until accessed by the patient. Typically, such data will be analyzed on a separate device (e.g., physician's computer workstation).
In alternative embodiments, however, in which the external device may comprise software to analyze the data in substantially real-time, the received RF signal with the sampled EEG may be analyzed by the EEG analysis algorithms to estimate the patient's brain state which is typically indicative of the patient's propensity for a neurological event (step 25). The neurological event may be a seizure, migraine headache, episode of depression, tremor, or the like. The estimation of the patient's brain state may cause generation of an output (step 27). The output may be in the form of a control signal to activate a therapeutic device (e.g., implanted in the patient, such as a vagus nerve stimulator, deep brain or cortical stimulator, implanted drug pump, etc.). In other embodiments, the output may be used to activate a user interface on the external device to produce an output communication to the patient. For example, the external device may be used to provide a substantially continuous output or periodic output communication to the patient that indicates their brain state and/or propensity for the neurological event. Such a communication could allow the patient to manually initiate therapy (e.g., wave wand over implanted vagus nerve stimulator, cortical, or deep brain stimulator, take a fast acting AED, etc.) or to make themselves safe.
In preferred embodiments, the return RF signal is transmitted (e.g., backscattered) immediately after sampling of the EEG signal to allow for substantially real-time transfer (and analysis) of the patient's EEG signals. In alternate embodiments, however, the return RF signal may be buffered in an internal memory and the communication transmission to the external device 14 may be delayed by any desired time period and may include the buffered EEG signal and/or a real-time sampled EEG signal. The return RF signal may use the same frequency as the illumination RF signal or it may be a different frequency as the illumination RF signal.
Unlike conventional digital implantable devices that send large packets of stored data with each return RF communication transmission, some embodiment of the methods and devices of the present invention substantially continuously sample physiological signals from the patient and communicate in real-time small amounts of data during each return RF signal communication. Because only small amounts of data (one or a small number of sampled EEG signals from each implantable device 12) are transmitted during each communication, a lower amount of power is consumed and the illumination of the implanted device from the incoming high-frequency RF signal will be sufficient to power the implantable device 12 for a time that is sufficient to allow for sampling of the patient's EEG signal. Consequently, in most embodiments no internal power source, such as a battery, is needed in the implantable device 12—which further reduces the package size of the implantable device 12.
The implantable devices 12 and the external devices 14 of the present invention typically use an electromagnetic field/high frequency communication link to both illuminate the implantable device and enable the high data transfer rates of the present invention. Conventional devices typically have an internally powered implantable device and use a slower communication link (e.g., that is designed for long link access delays) and transmit data out on a non-continuous basis. In contrast, some embodiments of the present invention uses a fast access communication link that transmits a smaller bursts of data (e.g., single or small number of EEG sample at a time) on a substantially continuous basis.
The frequencies used to illuminate and transfer data between the implantable devices 12 and external device are typically between 13.56 MHz and 10 GHz, preferably between 402 MHz and 2.4 GHz, more preferably between 900 MHz and 2.4 GHz. While it is possible to use frequencies above 2.4 GHz, Applicants have found that it is preferred to use a frequency below 2.4 GHz in order to limit attenuation effects caused by tissue. As can be appreciated, while the aforementioned frequencies are the preferred frequencies, the present invention is not limited to such frequencies and other frequencies that are higher and lower may also be used. For example, it may be desirable us use the MICS (Medical Implant Communication Service band) that is between 402-405 MHz to facilitate the communication link. In Europe, it may be desirable to use ETSI RFID allocation 869.4-869.65 MHz.
While not illustrated in
If desired, the data signals that are wirelessly transmitted from implantable device 12 may be encrypted prior to transmission to the control module 16. Alternatively, the data signals may be transmitted to the control module 16 as unencrypted data, and at some point prior to the storage of the data signals in the control module 16 or prior to transfer of the data signals to the physician's office, the EEG data may be encrypted so as to help ensure the privacy of the patient data.
Advantageously, the embodiment illustrated in
Housing 28 is typically in the form of a radially symmetrical, substantially cylindrical body that hermetically seals electronic components 30 disposed within a cavity 32. Housing 28 may be composed of a biocompatible material, such as glass, ceramic, liquid crystal polymer, or other materials that are inert and biocompatible to the human body and able to hermetically seal electronic components. Housing 28 may have embedded within or disposed thereon one or more x-ray visible markers 33 that allow for x-ray localization of the implantable device. Alternatively, one or more x-ray visible markers may be disposed within the cavity 32. Cavity 32 may be filled with an inert gas or liquid, such as an inert helium nitrogen mixture which may also be used to facilitate package leakage testing. Alternatively, it may be desirable to fill the cavity 32 with a liquid encapsulant (not shown) that hardens around the electronic components. The liquid encapsulant may comprise silicone, urethane, or other similar materials.
While housing 28 is illustrated as a substantially cylindrical body with the electrodes 24, 26 on opposing ends, housing may take any desired shape and the electrodes may be positioned at any position/orientation on the housing 28. For example, housing 28 may taper in one direction, be substantially spherical, substantially oval, substantially flat, or the like. Additionally or alternatively, the body may have one or more substantially planar surfaces so as to enhance the conformity to the patient's skull and to prevent rotation of the implantable device 12. While not shown, housing 28 may optionally include a conductive electromagnetic interference shield (EMI) that is configured to shield the electronic components 30 in housing 28. The EMI shield may be disposed on an inner surface of the housing, outer surface of the housing, or impregnated within the housing.
If desired, housing 28 may optionally comprise an anchoring assembly (not shown) that improves the anchoring of the implantable device 12 to the skull or the layers within the scalp. Such anchoring may be carried out with adhesive, spikes, barbs, protuberances, suture holes, sutures, screws or the like.
In the illustrated embodiment, first electrode 24 is disposed on a first end of housing 28 and is in electrical communication with the electronic components 30 through a hermetic feedthrough 34. Feedthrough 34 may be the same material as the first electrode 24 or it may be composed of a material that has a similar coefficient of thermal expansion as the housing 28 and/or the first electrode 24. Feedthrough 34 may make direct contact with a pad (not shown) on a printed circuit board 36, or any other type of conventional connection may be used (e.g., solder ball, bond wire, wire lead, or the like) to make an electrical connection to the printed circuit board 36.
Second electrode 26 may be spaced from a second, opposing end of the housing 28 via an elongated coil member 38. In the illustrated embodiment, the second electrode 26 typically comprises a protuberance 39 that is disposed within and attached to a distal end of the coil member 38. Coil member 38 acts as an electrical connection between second electrode and the electronic components 30 disposed within housing 28.
Coil member 38 will typically be composed of stainless steel, a high strength alloy such as MP35N, or a combination of materials such as a MP35N outer layer with silver core.
The illustrated embodiment shows that coil member 38 has a largest lateral dimension (e.g., diameter) that is less than the largest lateral dimension (e.g., diameter) of housing 28, but in other embodiments, the coil may have the same lateral dimension or larger lateral dimension from housing 28.
Coil member 38 may also be used as an antenna to facilitate the wireless transmission of power and data between the implantable device 12 and the external device 14 (or other device). In preferred embodiments, coil member 38 may be used to receive and transmit radiofrequency signals. In alternative embodiments, however, coil member 38 may be inductively coupled to an external coil to receive energy from a modulating, alternating magnetic field. Unlike other conventional implantable devices, the RF antenna is disposed outside of the housing 28 and extends from one end of housing 28. It should be appreciated however, that the present invention is not limited to a substantially cylindrical antenna extending from an end of the housing 28 and various other configurations are possible. For example, it may be desirable to wind the antenna around or within the housing 28. Furthermore, it may be desirable to use a substantially flat antenna (similar to RFID tags) to facilitate the transmission of power and data. To facilitate implantation, such antennas may be rolled into a cylindrical shape and biased to take the flat shape upon release from the introducer.
While not shown, it may also be desirable to provide a second antenna between the first electrode 24 and the housing 28. The second antenna may be used for power and downlink using a first frequency, e.g., 13.56 MHz, while the first antenna may be used for uplink using a second frequency, e.g., 902-928 MHz. In such embodiments, however, the implantable devices would need to have an internal timebase (e.g., oscillator and a frequency synthesizer). For the embodiments that use only a single frequency for the downlink and uplink, an internal timebase or frequency synthesizer is not needed—and the timebase established by the master (e.g., external device 14) can be used.
Coil member 38 may be in electrical communication with the electronic components 30 with a hermetic feedthrough 42 that extends through a via 44 in housing 28. Feedthrough 42 is typically composed of a material that has a coefficient of thermal expansion that is substantially similar to the material of housing 40. Because the coil member 38 is outside of the housing 28 the length of the implantable device 12 will be increased, but the flexible coil will be better exposed to the RF signals and will be allowed to conform to the shape of the patient's skull.
Coil member 38 is typically disposed outside of the housing 28 and disposed within an elongate, substantially flexible housing 40. Compared to the more rigid housing 28, the flexible housing 40 is better able to conform to the shape of an outer surface of the patient's skull, more comfortable for the patient and reduces the chance of tissue erosion. Flexible housing 40 may comprise silicone, polyurethane, or the like In the illustrated embodiment, flexible housing 40 extends along the entire length of coil member 38, but in other embodiments, flexible housing 40 may extend less than or longer than the longitudinal length of coil member 38. Flexible housing 40 will typically have a substantially cylindrical shape, but if desired a proximal end 46 of the cylindrical housing may be enlarged or otherwise shaped to substantially conform to a shape of the housing 28. The shaped proximal end 46 may be adhered or otherwise attached to the end of the housing 40 to improve the hermetic seal of the housing and may reduce any potential sharp edge or transition between the housings 28, 40. While
A longitudinal length of flexible housing 40 and the longitudinal length of the rigid housing 28 may vary depending on the specific embodiment, but a ratio of the longitudinal length of the flexible housing 40: the longitudinal length of the more rigid housing 28 is typically between about 0.5:1 and about 3:1, and preferably between about 1:1 and about 2:1. By having the longitudinal length of the flexible housing longer than the longitudinal length of the rigid housing, advantageously the implantable device will be more comfortable and better able to conform to the outer surface of the patient's skull. In alternative embodiments, it may also be desirable to have a longitudinal length of the rigid housing 28 be longer than the longitudinal length of the flexible housing 40, or in any other desired configuration.
Because the implantable devices 12 of the present invention consume a minimal amount of energy and use a high frequency RF coupling to power the device and communicate the EEG signals to the external device, unlike other conventional devices, some of the implantable devices 12 of the present invention will not need a ferrite core to store energy, and the electronic components 30 of the present invention will typically include aluminum or other MRI-safe material. Consequently, the patient's implanted with the implantable device 12 may safely undergo MRI imaging.
Feedthrough 42 that is connected to the coil member 38 extends from the end of coil member 38 and makes an electrical connection with a lead on the printed circuit board 36. The feedthrough 42 works in conjunction with one or more dielectric seals or spacers 52 to hermetically seal the cavity 32. Similar to above, the cavity 32 may be filled with an inert gas or an encapsulant. The proximal end 46 of flexible body 40 may be coupled to the seals 52 and/or coupled to the conductive body 48.
As shown in the embodiment of
In most embodiments, the implantable devices shown in
Such implantable devices 12 include an active electrode contact 400 that is in communication with one or more passive electrode contacts 401. The active electrode contact 400 may be used to facilitate monitoring of the physiological signals using the array of active and passive electrode contacts. The arrays of electrode contacts may be arranged in a linear orientation (
A thin or thick filmed microcircuit or a printed circuit board (“PCB”) 416 may be mounted onto an inner surface of the base 402. PCB 416 may have active components 418 (e.g., integrated circuits, ASIC, memory, etc.) and passive components 420 (e.g., resistors, capacitors, etc.) mounted thereto. Leads or bond wires 422 from the active and passive components may be electrically attached to pads on the PCB (not shown) which make electrical connections to leads or bond wires 424 that are attached to the hermetic feedthroughs 413. While not shown in
As noted above, the active contacts may be used in conjunction with one or more passive contacts to form an active implantable device 12 to facilitate monitoring of the patient's physiological signals and to communicate with the external device 14.
As shown in
The first and second electrodes will be used to sample a physiological signal from the patient—typically an EEG signal 53, and transmit the sampled signal to the electronic components 30. While it may be possible to record and transmit the analog EEG signal to the external device, the analog EEG signal will typically undergo processing before transmission to the external device 14. The electronic components typically include a printed circuit board that has, among others, an amplifier 54, one or more filters 56 (e.g., bandpass, notch, lowpass, and/or highpass) and an analog-to-digital converter 58. In some embodiments, the processed EEG signals may be sent to a transmit/receive sub-system 60 for wireless transmission to the external device via an antenna (e.g., coil member 38). Additional electronic components that might be useful in implantable device 12 may be found in U.S. Pat. Nos. 5,193,539, 5,193,540, 5,312,439, 5,324,316, 5,405,367 and 6,051,017.
In some alternative embodiments of the present invention, the electronic components 30 may include a memory 64 (e.g., RAM, EEPROM, Flash, etc.) for permanently or temporarily storing or buffering the processed EEG signal. For example, memory 64 may be used as a buffer to temporarily store the processed EEG signal if there are problems with transmitting the data to the external device. For example, if the external device's power supply is low, the memory in the external device is removed, or if the external device is out of communication range with the implantable device, the EEG signals may be temporarily buffered in memory 64 and the buffered EEG signals and the current sampled EEG signals may be transmitted to the external device when the problem has been corrected. If there are problems with the transmission of the data from the implantable device, the external device may be configured to provide a warning or other output signal to the patient to inform them to correct the problem. Upon correction of the problems, the implantable device may automatically continue the transfer the temporarily buffered data and the real-time EEG data to the memory in the external device.
The electronic components 30 may optionally comprise dedicated circuitry and/or a microprocessor 62 (referred to herein collectively as “microprocessor”) for further processing of the EEG signals prior to transmission to the external device. The microprocessor 62 may execute EEG analysis software, such as a seizure prediction algorithm, a seizure detection algorithm, safety algorithm, or portions of such algorithms, or portions thereof. For example, in some configurations, the microprocessor may run one or more feature extractors that extract features from the EEG signal that are relevant to the purpose of monitoring. Thus, if the system is being used for diagnosing or monitoring epileptic patients, the extracted features (either alone or in combination with other features) may be indicative or predictive of a seizure. Once the feature(s) are extracted, the microprocessor 62 may send the extracted feature(s) to the transmit/receive sub-system 60 for the wireless transmission to the external device and/or store the extracted feature(s) in memory 64. Because the transmission of the extracted features is likely to include less data than the EEG signal itself, such a configuration will likely reduce the bandwidth requirements for the communication link between the implantable device and the external device. Since the extracted features do not add a large amount of data to the data signal, in some embodiments, it may also be desirable to concurrently transmit both the extracted feature and the EEG signal. A detailed discussion of various embodiments of the internal/external placement of such algorithms are described in commonly owned U.S. patent application Ser. No. 11/322,150, filed Dec. 28, 2005 to Bland et al., the complete disclosure of which is incorporated herein by reference.
While most embodiments of the implantable device 12 are passive and does not need an internal power source or internal clock, in some embodiments, the electronic components 30 may include a rechargeable or non-rechargeable power supply 66 and an internal clock (not shown). The rechargeable or non-rechargeable power supply may be a battery, a capacitor, or the like. The rechargeable power supply 66 may also be in communication with the transmit/receive sub-system 60 so as to receive power from outside the body by inductive coupling, radiofrequency (RF) coupling, etc. Power supply 66 will generally be used to provide power to the other components of the implantable device. In such embodiments, the implanted device may generate and transmit its own signal with the sampled EEG signal for transmission back to the external device. Consequently, as used herein “transmit” includes both passive transmission of a signal back to the external device (e.g., backscattering of the RF signal) and internal generation of a separate signal for transmission back to the external device.
The EEG data may thereafter be stored in memory 72, such as a hard drive, RAM, permanent or removable Flash Memory, or the like and/or processed by a microprocessor 74 or other dedicated circuitry. Microprocessor 74 may be configured to request that the implantable device perform an impedance check between the first and second electrodes and/or other calibrations prior to EEG recording and/or during predetermined times during the recording period to ensure the proper function of the system.
The EEG data may be transmitted from memory 72 to microprocessor 74 where the data may optionally undergo additional processing. For example, if the EEG data is encrypted, it may be decrypted. The microprocessor 74 may also comprise one or more filters that filter out high-frequency artifacts (e.g., muscle movement artifacts, eye-blink artifacts, chewing, etc.) so as to prevent contamination of the high frequency components of the sampled EEG signals. In some embodiments, the microprocessor may process the EEG data to measure the patient's brain state, detect seizures, predict the onset of a future seizure, generate metrics/measurements of seizure activity, or the like. A more complete description of seizure detection algorithms, seizure prediction algorithms, and related components that may be implemented in the external device 14 may be found in pending, commonly owned U.S. patent application Ser. Nos. 11/321,897 and 11/321,898, filed on Dec. 28, 2005, to Leyde et al. and DiLorenzo et al., and 60/897,551, filed on Jan. 25, 2007, to Leyde et al., the complete disclosures of which are incorporated herein by reference.
It should be appreciated, however, that in some embodiments some or all of the computing power of the system of the present invention may be performed in a computer system or workstation 76 that is separate from the system 10, and the external device 14 may simply be used as a data collection device. In such embodiments, the personal computer 76 may be located at the physician's office or at the patient's home and the EEG data stored in memory 72 may be uploaded to the personal computer 76 via a USB interface 78, removal of the memory (e.g., Flash Memory stick), or other conventional communication protocols, and minimal processing may be performed in the external device 14. In such embodiments, the personal computer 76 may contain the filters, decryption algorithm, EEG analysis software, such as a prediction algorithm and/or detection algorithm, report generation software, or the like. Some embodiments of the present invention may take advantage of a web-based data monitoring/data transfer system, such as those described in U.S. Pat. Nos. 6,471,645 and 6,824,512, the complete disclosures of which are incorporated herein by reference.
External device 14 may also comprise an RF signal generator 75 that is configured to generate the RF field for interrogating and optionally powering the implanted devices 12. RF generator 75 will be under control of the microprocessor 74 and generate the appropriate RF field to facilitate monitoring and transmission of the sampled EEG signals to the external device.
External device 14 will typically include a user interface 80 for displaying outputs to the patient and for receiving inputs from the patient. The user interface typically comprise outputs such as auditory devices (e.g., speakers) visual devices (e.g., LCD display, LEDs to indicate brain state or propensity to seizure), tactile devices (e.g., vibratory mechanisms), or the like, and inputs, such as a plurality of buttons, a touch screen, and/or a scroll wheel.
The user interface may be adapted to allow the patient to indicate and record certain events. For example, the patient may indicate that medication has been taken, the dosage, the type of medication, meal intake, sleep, drowsiness, occurrence of an aura, occurrence of a seizure, or the like. Such inputs may be used in conjunction with the recorded EEG data to improve the analysis of the patient's condition and determine the efficacy of the medications taken by the patient.
The LCD display of the user interface 80 may be used to output a variety of different communications to the patient including, status of the device (e.g., memory capacity remaining), battery state of one or more components of system, whether or not the external device 14 is within communication range of the implantable devices 12, brain state indicators (e.g., a warning (e.g., seizure warning), a prediction (e.g., seizure prediction), unknown brain state, safety indication, a recommendation (e.g., “take drugs”), or the like). Of course, it may be desirable to provide an audio output or vibratory output to the patient in addition to or as an alternative to the visual display on the LCD. In other embodiments, the brain state indicators may be separate from the LCD display to as to provide a clear separation between the device status outputs and the brain state indicators. In such embodiments, the external device may comprise different colored LEDs to indicate different brain states. For example, a green LED may indicate a safe brain state, a yellow light may indicate an unknown brain state, and a red light may indicate either a seizure detection or seizure prediction.
External device may also include a medical grade power source 82 or other conventional power supply that is in communication with at least one other component of external device 14. The power source 82 may be rechargeable. If the power source 80 is rechargeable, the power source may optionally have an interface for communication with a charger 84. While not shown in
In use, one or more of the implantable devices are implanted in the patient. The implanted device is interrogated and powered so that the EEG signals are sampled from the patient's brain. The EEG signals are processed by the implanted device and the processed EEG signals are wirelessly transmitted from the implanted device(s) to an external device. The EEG signals are stored for future or substantially real-time analysis.
As noted above, in preferred embodiments, the implantable devices are implanted in a minimally invasive fashion under the patient's scalp and above an outer surface of the skull.
While not shown in
Advantageously, the implantable devices are able to monitor EEG signals from the patient without the use of burr holes in the skull or implantation within the brain—which significantly reduces the risk of infection for the patient and makes the implantation process easier. While there is some attenuation of the EEG signals and movement artifacts in the signals, because the implantable devices are below the skin, it is believed that there will be much lower impedance than scalp electrodes. Furthermore, having a compact implantable device 14 below the skin reduces common-mode interference signals which can cause a differential signal to appear due to any imbalance in electrode impedance and the skin provides some protection from interference caused by stray electric charges (static).
Once implanted in the patient, the monitoring systems 10 of the present invention may be used for a variety of different uses. For example, in one usage the systems of the present invention may be used to diagnose whether or not the patient has epilepsy. Patients are often admitted to video-EEG monitoring sessions in an EMU to determine if the patient is having seizures, pseudo-seizures, or is suffering from vaso-vagal syncope, and the like. Unfortunately, if the patient has infrequent “seizures,” it is unlikely that the short term stay in the EMU will record a patient's seizure and the patient's diagnose will still be unclear. Consequently, in order to improve the patient's diagnosis, in addition to the in-hospital video-EEG monitoring or as an alternative to the in-hospital video-EEG monitoring, the patient may undergo an ambulatory, long term monitoring of the patient's EEG using the system of the present invention for a desired time period. The time period may be one day or more, a week or more, one month or more, two months or more, three months or more, six months or more, one year or more, or any other desired time period in between. The patient may be implanted with the system 10 using the method described above, and after a predetermined time period, the patient may return to the physician's office where the EEG data will be uploaded to the physician's personal computer for analysis. A conventional or proprietary seizure detection algorithm may be applied to the EEG data to determine whether or not a seizure occurred in the monitoring time period. If it is determined that one or more seizures occurred during the monitoring period, the seizure detection algorithm may be used to provide an output to the physician (and/or generate a report for the patient) indicating the occurrence of one or more seizures, and various seizure activity metrics, such as spike count over a period of time, seizure count over a period of time, average seizure duration over a period of time, the pattern of seizure occurrence over time, and other seizure and seizure related metrics. In addition, the software may be used to display the actual EEG signals from specific events or selected events for physician confirmation of seizure activity. Such data may be used as a “baseline” for the patient when used in assessing efficacy of AEDs or other therapies that the patient will undergo.
If the patient has been diagnosed with epilepsy (either using the system of the present invention or through conventional diagnosis methods), the present invention may also be used to determine the epilepsy classification and/or seizure type. To perform such methods, a desired number of implantable devices may be implanted in the patient for the long term monitoring of the patient's pattern of electrical activity in the different portions of the patient's brain. Such monitoring will be able to provide insight on whether or not the patient has partial/focal seizures or generalized seizures. In the event that the patient's epilepsy classification is already known, the classification may determine the desired placement for the implantable devices in the patient. For patients suspected or known to have temporal lobe epilepsy, the implantable devices will likely be focused over the temporal lobe and adjacent and/or over the regions of epileptiform activity. Likewise, for patient's suspected or known to have parietal lobe epilepsy, some or all of the implantable devices will be positioned over the parietal lobe and adjacent and/or over the regions of epileptiform activity. Furthermore, if the seizure focus or foci are known, at least some of the implantable devices may be positioned over the seizure focus or foci and some may be positioned contralateral to the known seizure focus or foci.
If a seizure focus in the patient has not been lateralized, the present invention may be used to lateralize the seizure focus.
In another use, the present invention may be used to quantify seizure activity statistics for the patient. The most common method of quantifying a patient's seizure activity is through patient self reporting using a seizure diary. Unfortunately, it has been estimated that up to 63% of all seizures are missed by patients. Patient's missing the seizures are usually caused by the patients being amnesic to the seizures, unaware of the seizures, mentally incapacitated, the seizures occur during sleep, or the like.
Seizure frequency—How frequent does the patient have seizures? What is the seizure frequency without medication and with medication? Without electrical stimulation and with electrical stimulation?
Finally, at step 152, report generation software may be used to generate a report based on the statistics for the seizure activity. The report may include some or all of the statistics described above, an epilepsy/no epilepsy diagnosis, identification of a seizure focus, and may also include the EEG signal(s) associated with one or more of the seizures. The report may include text, graphs, charts, images, or a combination thereof so as to present the information to the physician and/or patient in an actionable format. Advantageously, the systems may be used to generate a baseline report for the patient, and the system may be continuously used to record data over a long period of time and provide a quantification of the patient's change in their condition and/or the efficacy of any therapy that the patient is undergoing (described in more detail below).
As noted above, the present invention enables the documentation and long term monitoring of sub-clinical seizures in a patient. Because the patient is unaware of the occurrence of sub-clinical seizures, heretofore the long term monitoring of sub-clinical seizures was not possible. Documentation of the sub-clinical seizures may further provide insight into the relationship between sub-clinical seizures and clinical seizures, may provide important additional information relevant to the effectiveness of patient therapy, and may further enhance the development of additional treatments for epilepsy.
By way of example, a medically refractory patient coming to an epilepsy center for the first time might first have the system of the present invention implanted and then asked to collect data for a prescribed time period, e.g., 30 days. The initial 30 days could be used to establish a baseline measurement for future reference. The physician could then prescribe an adjustment to the patient's medications and have the patient collect data for another time period, e.g., an additional 30 day period. Metrics from this analysis could then be compared to the previous analysis to see if the adjustment to the medications resulted in an improvement. If the improvement was not satisfactory, the patient can be taken off of the unsatisfactory medication, and a new medication could be tried. This process could continue until a satisfactory level of seizure control was achieved. The present invention provides a metric that allows physicians and patients to make informed decisions on the effectiveness and non-effectiveness of the medications.
At step 166, the therapy that is to be evaluated is commenced. The therapy will typically be an AED and the patient will typically have instructions from the neurologist, epileptologist, or drug-manufacturer regarding the treatment regimen for the AED. The treatment regimen may be constant (e.g., one pill a day) throughout the evaluation period, or the treatment regimen may call for varying of some parameter of the therapy (e.g., three pills a day for the first week, two pills a day for the second week, one pill a day for the third week, etc.) during the evaluation period. During the evaluation period, the implantable device(s) will be used to substantially continuously sample the patient's EEG and assess the effect that the AED has on the patient's EEG. The sampled EEG may thereafter be processed to obtain a follow-up measurement for the patient (Step 168). If the baseline measurement was seizure statistics for the baseline time period, then the follow-up measurement will be the corresponding seizure statistics for the evaluation period. At step 170, the baseline measurement is compared to the follow-up measurement to evaluate the therapy. If the comparison indicates that the therapy did not significantly change the patient's baseline, the therapy may be stopped, and other therapies may be tried.
Currently, the primary metric in evaluating the efficacy of an AED is whether or not the AED reduces the patient's seizure count. In addition to seizure count, the systems of the present invention would be able to track any reduction in seizure duration, modification in seizure patterns, reduction in seizure frequency, or the like. While seizure count is important, because the present invention is able to provide much greater detail than just seizure count, efficacy of an AED may be measured using a combination of additional metrics, if desired. For example, if the patient was having a large number of sub-clinical seizures (which the patient was not aware of) and the AED was effective in reducing or stopping the sub-clinical seizures, the systems of the present invention would be able to provide metrics for such a situation. With conventional patient diary “metrics”, the patient and physician would not be aware of such a reduction, and such an AED would be determined to be non-efficacious for the patient. However, because the present invention is able to provide metrics for the sub-clinical seizures, the efficacious medication could be continued, if desired.
At step 172, the epileptologist or neurologist may decide to change one or more parameters of the therapy. For example, they may change a dosage, frequency of dosage, form of the therapy or the like, and thereafter repeat the follow-up analysis for the therapy with the changed parameter. After the “second” follow up measurement is complete, the second follow up data may be obtained and thereafter compared to the “first” follow up measurements and/or the baseline measurements. While not shown in
In addition to evaluating an efficacy of a therapy for an individual patient, the metrics that are provided by the present invention also enable an intelligent titration of a patient's medications. As shown in
At step 190, the patient's EEG is monitored and processed to obtain a second patient data measurement for the patient (e.g., follow-up data measurement). If the neurologist or epileptologist is satisfied with the results, the titration may end. But in many embodiments, the titration process will require more than one modification of parameters of the therapy. In such embodiments, the second therapy is stopped (step 192), and a therapy with Nth parameters (e.g., third, fourth, fifth . . . ) is commenced (step 194). Monitoring and processing of the patient's EEG signals are repeated (step 196), and the process is repeated a desired number of times (as illustrated by arrow 197). Once the desired numbers of modifications to the therapy have been made, the various patient data measurements may be analyzed (e.g., compared to each other) to determine the most desirous parameters for the therapy (step 198). As can be imagined, any number of different analyses or statistical methods may be performed. In one embodiment, seizure activity statistics (e.g., clinical seizure frequency, sub-clinical seizure frequency, seizure rate per time period, seizure duration, seizure patterns, etc.) may be used to assess the efficacy and differences between the therapies.
With the instrumentation provided by the present invention, the process of selecting appropriate AEDs and the titration of dosages of such AEDs could occur much faster and with much greater insight than ever before. Further, the chance of a patient remaining on an incremental AED that was providing little incremental benefit would be minimized. Once a patient was under control, the patient could cease the use of the system, but the implantable device could remain in the patient. In the future, the patient might be asked to use the system again should their condition change or if the efficacy of the AED wane due to tolerance effects, etc.
Furthermore, the systems of the present invention will also be able to provide metrics for the effectiveness of changes to various electrical parameters (e.g., frequency, pulse amplitude, pulse width, pulses per burst, burst frequency, burst/no-burst, duty cycle, etc.) for the electrical stimulation treatments. Such metrics will provide a reliable indication regarding the effectiveness of such parameter changes, and could lead to optimization of stimulation for parameters for individual patients or the patient population as a whole.
In addition to facilitating the selection of appropriate AEDs and titration of dosages of the AEDs for an individual patient, the present invention may have beneficial use in the clinical trials for the development of experimental AEDs and other therapies for the epileptic patient population (and other neurological conditions). One of the greatest barriers to developing new AEDs (and other pharmacological agents) is the costs and difficulties associated with the clinical trials. Presently, the standard metric for such clinical trials is patient seizure count. Because this metric is self-reported and presently so unreliable, to power the study appropriately clinical trials for AEDs must involve very large patient populations, in which the patient's must have a high seizure count. At an estimated cost of $20,000 per patient for pharmacological trials, the cost of developing a new drug for epilepsy is exceedingly high and may deter drug companies from developing AEDs.
The minimally invasive systems of the present invention may be used to facilitate these clinical trials. Such systems could result in significantly more reliable data, which would result in much smaller sample patient populations, and could include a broader types of patients (e.g., patient's who don't have frequent seizures) for appropriately powering the study. Improved certainty in efficacy would also reduce risk to the company, as it moved from safety studies to efficacy studies. Significantly reducing risk and improving the economics of these studies by reducing the required number of study subjects could lead to an increase in the development of new therapies for this patient population, and other patient populations.
It should be appreciated however, that the present invention is not limited to clinical trials for epilepsy therapies, and the present invention has equal applicability to other clinical trials (e.g., cancer therapy, cardiac therapy, therapy for other neurological disorders, therapy for psychiatric disorders, or the like.)
At step 204, the sampled EEG signals are processed for a desired time period to obtain a first patient data measurement, e.g., a baseline data measurement, for each of the participants in the clinical trial. After the participants have commenced the experimental therapy (typically by following a prescribed treatment regimen by the investigator or drug company), the same implantable devices are used to sample the EEG signals from the participant for an evaluation period, and the EEG signals are processed to provide a second patient data measurement, e.g., follow-up measurement (Step 206, 208). At step 210, the baseline data measurement and the follow-up data measurement may be compared using conventional statistical methods in order to evaluate the experimental therapy on the patient population.
While not shown in
The baseline period and the evaluation period are typically the same time length. The time length may be any desired time, but is typically at least one week, and preferably between at least one month and at least three months.
Evaluation of the experimental therapy may be to evaluate dosing requirements, evaluate toxicity of the experimental therapy, evaluate long-term adverse effects of the experimental therapy or to determine efficacy of the experimental therapy. In one preferred embodiment, the comparison may simply determine whether there was a statistically significant change in a seizure count between the baseline period and the evaluation period. But as noted above, the baseline data measurement and follow-up data measurement may include any metric that is extracted from the EEG signals.
At step 226, the sampled EEG signals are processed to obtain a first patient data measurement, e.g., a baseline data measurement, for each of the participants in the clinical trial. If the patient's do not have any seizures during the baseline period, then the patient's will most likely be excluded from the remainder of the clinical trial. The remaining participants in the clinical trial are then broken into an intervention group and a control group. The experimental therapy is commenced in the intervention group of the patient population (step 228), and a placebo therapy is commenced in the control group of the patient population (step 230).
The implantable devices are used to substantially continuously sample the EEG signals of both the intervention group and the control group during an evaluation period. The EEG signals are processed to obtain follow-up seizure activity data (or some other metric) for both groups (step 232, 234). Thereafter, the baseline data and the follow up data for both the intervention group and the control group are analyzed, (e.g., compared with each other) to evaluate the efficacy of the experimental therapy for the patient population (step 236). While not shown in
While the preferred embodiments described above are directed toward evaluating experimental AEDs in the clinical trial, the present invention is equally applicable to clinical trials for other experimental pharmacological agents, biologics, devices, and other non-pharmacological therapies. For example, the present invention may also be used to evaluate the Vagus Nerve Stimulator (sold by Cyberonics Corporation), Responsive Neurostimulator (RNS) (manufactured by NeuroPace Corporation), Deep Brain Stimulators manufactured by Medtronic, and other commercial and experimental neural and spinal cord stimulators. The minimally invasive systems of the present invention may be implanted in patients who are equipped with any of the above stimulators to provide metrics regarding the efficacy of the electrical stimulation treatments.
Furthermore, the systems of the present invention will also be able to provide metrics for the effectiveness of changes to various electrical parameters (e.g., frequency, pulse amplitude, pulse width, pulses per burst, burst frequency, burst/no-burst, etc.) for the electrical stimulation treatments. Such metrics will provide a reliable indication regarding the effectiveness of such parameter changes, and could lead to optimization of stimulation for parameters for individual patients or the patient population as a whole.
While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. For example, the present invention also encompasses other more invasive embodiments which may be used to monitor the patient's neurological system.
Alternative embodiments of the implantable device of the present invention may require a neurosurgeon to create a more invasive incision in the patient's scalp. For example, it may be desirable to use a low profile device that is not substantially cylindrical, but instead is substantially planar or concave so as to conform to the curvature of the patient's skull. Such embodiments would likely not be able to be implanted without general anesthesia and may require a surgeon to implant the device.
On the other hand, in some embodiments it may be desirable to be completely non-invasive. Such embodiments include “implantable” devices 12 that are not actually implanted, but instead are “wearable” and may be attached to the outer surface of the skin with adhesive or a bandage so as to maintain contact with the patient's skin. For example, it may be possible to surface mount the device 12 behind the ears, in the scalp, on the forehead, along the jaw, or the like. Because the electrodes are wireless and are such a small size, unlike conventional electrodes, the visual appearance of the electrodes will be minimal.
Furthermore, in some embodiments, it may be desirable to modify the implantable device 12 to provide stimulation to the patient. In such embodiments, the implantable device 12 will include a pulse generator and associated hardware and software for delivering stimulation to the patient through the first and second electrodes 24, 26 (or other electrodes coupled to the device. In such embodiments, the external device 14 will include the hardware and software to generate the control signals for delivering the electrical stimulation to the patient.
While the above embodiments describe that power to the implanted devices may be derived wirelessly from an external device and/or from a battery in the implanted device, it should be appreciated that the internal devices may derive or otherwise “scavenge” power from other types of conventional or proprietary assemblies. Such scavenging methods may be used in conjunction with the external power source and/or the internal power source, or it may be used by itself to provide the necessary power for the implanted devices. For example, the implanted devices may include circuitry and other assemblies (e.g., a microgenerator) that derive and store power from patient-based energy sources such as kinetic movement/vibrations (e.g., gross body movements), movement of organs or other bodily fluids (e.g., heart, lungs, blood flow), and thermal sources in the body (e.g., temperature differences and variations across tissue). As can be imagined, such technology could reduce or eliminate the need for recharging of an implanted battery, replacement of a depleted battery, and/or the creation of an external RF field—and would improve the ease of use of the devices by the patients.
Some embodiments of the monitoring system may include an integral patient diary functionality. The patient diary may be a module in the external device and inputs by the patient may be used to provide secondary inputs to provide background information for the sampled EEG signals. For example, if a seizure is recorded, the seizure diary may provide insight regarding a trigger to the seizure, or the like. The diary may automatically record the time and date of the entry by the patient. Entries by the patient may be a voice recording, or through activation of user inputs on the external device. The diary may be used to indicate the occurrence of an aura, occurrence of a seizure, the consumption of a meal, missed meal, delayed meal, activities being performed, consumption of alcohol, the patient's sleep state (drowsy, going to sleep, waking up, etc.), mental state (e.g., depressed, excited, stressed), intake of their AEDs, medication changes, missed dosage of medication, menstrual cycle, illness, or the like. Thereafter, the patient inputs recorded in the diary may also be used by the physician in assessing the patient's epilepsy state and/or determine the efficacy of the current treatment. Furthermore, the physician may be able to compare the number of seizures logged by the patient to the number of seizures detected by the seizure detection algorithm.
It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
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