WO2007118560A2

WO2007118560A2 - Automatic detection of hypopnoeas

Info

Publication number: WO2007118560A2
Application number: PCT/EP2007/002093
Authority: WO
Inventors: Christian Weigand; Matthias Struck
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2006-04-12
Filing date: 2007-03-09
Publication date: 2007-10-25
Also published as: DE102006017279A1; WO2007118560A3

Abstract

The occurrence of a hypopnoea can be detected with high reliability based on a recorded number of sample values describing a respiratory sound if an energetic value is calculated from the sample values, said value describing the energy contained in the respiratory sound within a given period. The occurrence of an hypopnoea can be detected by carrying out the energetic value with a variable reference value which depends on the respective patient, thereby eliminating negative external influences such as e.g. different sensitivities of the microphone or different noise intensities of the respiratory sound of different patients.

Description

Automatic detection of hypopneas

description

The present invention is concerned with methods for the automatic detection of sleep disorders, and more particularly with an apparatus and method that provide a means for the automated detection of hypopneas.

Sleep disorders are an increasingly common phenomenon that severely limits the quality of life and performance of those affected. In addition, with special types of occurring sleep disorders, the health of the patient can be permanently impaired.

Two particularly common sleep disorders are apneas and hypopneas. In apnea, short-term complete respiratory arrest occurs, the frequency of which can vary widely, and values of over 35 such sleep disorders per night are not uncommon. The general definition for the clinical picture of apnea is the occurrence of at least 10 respiratory arrest, each lasting at least 10 seconds, within one hour of sleep. Apnea may have several causes, the most common one being upper respiratory obstruction occurring during sleep (obstructive sleep apnea). The closure is usually triggered by a relaxation of the velum, which is among other things responsible for the snoring. If the soft palate relaxes, it can cause it to completely close off the respiratory tract, interrupting the supply of oxygen to the lungs and thus to the brain. Due to the above relationship, apnea is also commonly seen in individuals prone to severe snoring. loading Due to the decreasing oxygen content of the blood, the heart rate decreases and the blood pressure drops. This drop in the vital parameters triggers an alarm signal or a countermeasure in the brain after a certain time, so that, for example triggered by increased adrenaline, the affected persons experience a so-called arousal at the end of an apnea. In the case of the arousal, the affected patient typically starts with a loud snoring sound, whereupon breathing resumes. Heart rate and oxygen levels can normalize. Since, as described above, this process is repeated several times a night, it is apparent that sleep apnea can cause a number of negative side effects, such as increased daytime fatigue, decreased mental and physical performance, poor concentration, headache, depression, and the like.

In addition to obstructive apnea, the so-called central sleep apnea is frequently observed, in which there is no obstruction of the respiratory tract, but rather is due to an interruption of the respiratory impulses on the part of the brain. The observable course of apnea to the atrial is essentially the same as in obstructive apnea.

A disease closely related to apnea is the hypopnea, for which there is no clear classification. In hypopnea, the volume of breath during sleep is greatly reduced during sleep for the duration of the hypopnea, so that the hypopnea leads to a reduction in the oxygen content in the blood as well as the heart rate. Due to the same symptoms, the health damage that can be caused by hypopneas is similarly severe as described above in the case of apneas. However, in contrast to apnea, in the case of hypopnea the observation of the arousal, ie the intense, short-term growth process, is, as a rule not possible. However, as with apnea, patients who snore are significantly more affected by hypopnoea.

In the following, a typical signal course, as occurs when apnea or hypopnea occurs, will be briefly described below with reference to FIGS. 3a and 3b. FIG. 3a describes an apnea event and FIG. 3b a hypopnoenic event, the time being plotted in both representations on the X-axis and the amplitude course of the breathing noise of a sleeping patient recorded by means of a microphone on the Y-axis is.

FIG. 3 a shows a normal sleep rhythm in a first region 2, in which a slight snoring sound is detected at approximately regular intervals. In addition, FIG. 3 a shows the apnea region 4, in which the arrest occurs and within which consequently no signal amplitude is recorded. Immediately after the apnea region 4, an arousal region 6 can be seen in FIG. 3a, which, as already described above, is characterized in that at the end of the apnea the patient resumes breathing with loud snoring, which is why in the arousal region 6 there are higher amplitudes recorded as in the first area 2, in which the patient still sleeps normally. Immediately before the apnea region 4, an indicator region 8, which precedes the apnea region 4 and within which the recorded amplitudes or the recorded signal shape differs clearly from the signals in the first region 2, in which the patient is in one normal sleep phase is located. The indicator region is typical of the occurrence of an apnea event, that is, such a waveform is typically observed prior to onset of apnea respiratory failure in all patients. The acoustic impression is about that of a short powerful snoring, which can often be associated with a slight groan. A way to prove a Apnea is therefore z. Example, in the recorded snoring noise to detect such a waveform.

3b shows the occurrence of a hypopnea, wherein in FIG. 3b a sleep area 10 can first be identified by the patient being in a normal sleep state and in which snoring or respiratory sounds of significant amplitude are recorded in approximately equidistant sections. In the hypopnea area 12, in which, as already described above, the respiratory flow is greatly reduced, only an extremely low respiratory sound is then recorded for a period of more than 30 seconds. It should be noted that the hypopnea is not preceded by a typical signal course such as the indicator area 8 of the apnea. This was confirmed by the observation of a variety of hypopnea events in different patients.

The prior art describes a number of methods used to automatically detect the onset of apnea. US patent application US 2004 / 0225226A1 and US Pat. No. 6,935,335B1 describe a method in which one or more microphones are used, which transmit the signals recorded by them to a digital signal processor, which signals the beginning of an apnea. Event can prove. The signal processing performs a Fourier transformation into the frequency domain and determines, by analyzing a large number of Fourier coefficients, whether there is a signal that indicates the beginning of an apnea event. This method has the great disadvantage that the Fourier analysis generates a very large number of Fourier coefficients as a representation of the recorded signal. Real-time processing is made considerably more difficult because a simple criterion indicating the occurrence of apnea can not be found can, if for determining such a criterion, the plurality of Fourier coefficients must be used.

European Patent EP 0504945B1 describes how apnea events can be detected when both respiratory and heart rate sounds are recorded. In this case, a threshold value comparison is essentially carried out to evaluate the recorded tones. This means that an apnea is closed when one of the signals exceeds or falls below a certain predetermined limit value. In this case, the threshold value comparison can additionally be carried out in a frequency-selective manner by dividing the recorded signal into fixed frequency ranges, wherein each frequency range can have its own threshold value. The method described here has the disadvantage that a threshold value comparison can use only a single criterion, namely the energy value on which the threshold value calculation is based, in order to detect the occurrence of an apnea. The use of this single integral information usually does not make it possible to recognize the characteristic signal course, which is not only characterized by its integrated intensity, before the onset of apnea with sufficiently high reliability.

U.S. Patent 5,123,425 describes a collar suitable for detecting and treating apnea events using a microphone as a sensor. The detection of an apnea event is also made here by simply exceeding the threshold, so that the same disadvantages as described above must be accepted.

The German patent DE 69632015T2 describes a sleep apnea treatment device, by means of which the ventilation pressure of a breathing mask can be variably adapted to the sleep state of a patient. In this case, the detection of the sleep state, a sensor such as uses a microphone that records a respiratory signal within the frequency range of 20 Hz to 20,000 KHz and dynamically changes the breathing pressure to avoid apnea events based on this signal.

European Patent Application 0371424A1 describes a monitoring device for the diagnosis of apnea, in which both the heart rate and respiratory sounds are recorded and in which the onset of an apnea event is concluded on the basis of simple threshold comparisons of both the heart rate and the respiratory volume.

The described methods, which are based on a simple threshold comparison, have the great disadvantage in apnea detection that only an integral value is used as a criterion for whether an apnea has started or not. Therefore, a reliable detection is usually not possible because of this, the characteristic waveform must be considered, which is not possible due to the integral property in the threshold comparison.

In the detection of hypopneas, the threshold method has the great disadvantage that a fixed threshold value can not reliably detect hypopnea, since it is characterized in that during the occurrence of the hypopnea there is still a breath noise whose volume can vary compared to the normal breath volume and that is also highly patient-dependent.

The great disadvantage of detecting a start of an apnea by means of Fourier analysis is that a multiplicity of Fourier coefficients is generated by the Fourier analysis, which describe the frequency spectrum of the recorded noise. A simple and thus meaningful computing time durchfuhrbarer test or characterization of these Fourier coefficients is hardly possible due to their large number in real time. Even before the onset of respiratory Due to the complexity of the characterization, it is impossible to predict levels of apnea.

The object of the present invention is to provide a device and a method which enable the detection of hypopneas more reliably than hitherto.

This object is achieved by a device according to claim 1 and by a method according to claim 13.

The present invention is based on the finding that the occurrence of a hypopnea based on a recorded series of sample values which describe a respiratory sound can be detected with greater reliability when an energy value from the sample values is calculated, which is calculated within one describes energy contained in the respiratory sound predetermined time interval. According to the invention, the occurrence of a hypopnea is demonstrated by comparing the energy value with a variable reference value dependent on the respective patient, so that external environmental influences such as variable sensitivities of the microphone or different volumes of breathing noise of different patients have no negative effects can have the recognition performance.

In one embodiment of the present invention, therefore, the energy value calculated for a fixed time interval is compared with a reference value which is calculated from a plurality of energy values preceding the current energy value. To determine the reference value, the breathing noise of the patient in question is thus used himself, which was recorded under the current environmental conditions and which thus is specific for the patient under the given environmental conditions. As a result, the detection behavior compared to the State of the art corresponding method with fixed threshold extremely improved.

For example, in one embodiment of the present invention, the reference value is determined as an average of a predetermined number of previous energy values. This is equivalent to using energy values that are normalized to the current reference energies for the comparison of the energy value with a reference value.

In a further exemplary embodiment of the present invention, a hypopnea is only displayed if a plurality of successive energy values fulfill the hyponucleus criterion, ie if the energy content of a plurality of successive signal sections (with a fixed number of sample values) lies below a variable, patient-specific threshold value.

In an exemplary embodiment of the present invention, the amplitude values of the recorded respiratory noise sampled at a predetermined frequency are used as sample values, suitable sampling frequencies for example lying between 5 kHz and 25 kHz.

Preferably, the sampled amplitude is stored in digital values, which digitization may be done, for example, to an accuracy of less than 12 bits.

In a further exemplary embodiment of the present invention, an energy value is formed for each discrete window length, that is to say for a fixed number of successive sample values, as a quadratic sum of the sample values sampled within the window length. This has the great advantage that the quadratic summation of discrete, digitized quantities represents a mathematically extremely simple and therefore fast to perform operation. For determining the hypopnoen criterion, in another embodiment the amplitude value generated by quadratic addition is normalized before further processing. Normalization achieves independence from the specific patient or from his or her breathing noise volume and from other signals that may distort the signal (variable microphone sensitivity).

In another embodiment of the present invention, a laryngeal microphone is used to receive the breathing sound, which has the great advantage that the sound transmission to the laryngeal microphone takes place by means of mechanical coupling, so that any other ambient noise, such as road noise or snoring noises from bed neighbors results in the measurement can not falsify.

Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. Show it:

1 shows an example of a device for the detection of hypopneas;

2 shows an example of section-wise processing of sample values according to the invention;

3a shows an example of a breathing sound course during an apnea; and

3b shows an example of a breathing sound course during a hypopnea.

1 shows an example of a device for detecting the onset of apnea, wherein the detection is performed using a series of sample values describing a patient's breathing sound. Shown are an analyzer 20 and an evaluation device 22 as well as an optional microphone 24 with a scanning unit 26. According to the invention, an energy value is determined by the analyzer 20 using the series of sample values for a respective predetermined time interval of respiratory noise, which within a time interval in FIG Respiratory sound contains energy.

The energy value thus determined is transmitted to the evaluation device 22, which can detect the occurrence of hypopnea by comparing the energy value with a variable reference value dependent on the patient.

_(. Tj), for example, the discrete sample values, that is, the sample values S given an example for the calculation of a meaningful energy value is the square sum of the samples in the interval t _{1 =} o to t _{1 =} i:

According to the evaluation device 22, the energy signal obtained in this way is not compared with a previously programmed value, but instead with a variable, patient-dependent reference value, so that the system allows maximum flexibility and resulting maximum recognition accuracy, as this itself responds to the snoring volume or snoring volume can adjust the snoring behavior of the patient to be examined. For this purpose, in the threshold comparison, either the energy value of the currently considered time window is normalized to the energy of the preceding time window, or the reference value itself is constantly updated. For example, the reference value may be calculated as the average of a number of previous energy values (floating average). If the currently considered energy value E _{f +} i, then the reference energy value For example, R can be calculated according to the following formula:

1 /

R = -xYE, J ι = l

In another embodiment of the present invention, it is also possible to determine the variable patient-dependent reference energy during a training phase of the apparatus during which a hypopnea-sensing device of the present invention determines the average snoring energy of a specific patient and stores it in a memory. When using the device according to the invention, the patient can then select, for example, its configuration from a menu, so that in this case the evaluation device 22 can compare the energy values with variable reference values dependent on the patient in order to achieve the optimum recognition performance according to the invention.

The series of sample values which describe the respiratory sound can either be recorded spatially separated from the device according to the invention and then made available, for example, in the form of a transportable data carrier or by means of a wireless data interface. In another embodiment of the present invention, as indicated in FIG. 1, a sampling unit 26 is connected to the analyzer 20, which digitizes the signals received by a microphone 24 connected to the sampling unit 26 at a predetermined sampling frequency. The sampling frequency is not prescribed in any way, it may for example be 5, 11 or 22 kHz. The transmission between the scanning unit 26 and the analyzer 20 can in turn be arbitrary, in particular also be done wirelessly or via a data network such as the Internet. The same connection methods are also conceivable in principle for the connection between the microphone 24 and the scanning unit 26, so that the inventive concept as a whole can not be used in any way. is limited by the way the series of sample values describing the breath noise are recorded or generated in order to be made available to the analyzer 20.

Fig. 2 shows how the series of sample values is generated according to the invention and how the predetermined time interval for which an energy value is calculated can be determined. 2 shows the time in arbitrary units on the X-axis and the amplitude of a measured signal on the Y-axis also in arbitrary units.

Shown is a signal course 30 to be analyzed, which is sampled in equidistant time intervals of the length 32, so that an amplitude value s (ti) is present in digital form at any point in time. In this case, the digitization accuracy, ie the number of bits representing a single amplitude value, can be freely varied within wide limits. FIG. 2 furthermore shows a first time window 34a and a second time window 34b, for each of which an individual energy value is determined. The energy values can be determined, for example, as described above, by quadratic addition of the amplitude values SIt ₁ ). This simple mathematical operation is real-time. In this case, a length of a time window can be, for example, 200 ms, but the length is variable within wide limits since the length of a hypnotic event, as can be seen from FIG. 3b, is typically 30 seconds or more. Preferred words are in the interval between 100 ms and 500 ms. By suitable length of the time window and the period of time provided for normalizing the energy values (typically several tens of seconds), the variability, ie the patient's individuality, and thus also the detection efficiency of the device according to the invention, can be further improved.

In a preferred exemplary embodiment of the present invention, the evaluation device 22 shows the occurrence a hypopnea only when a plurality of successive time windows 34a and 34b, respectively, indicate the occurrence of hypopnea when compared to the variable reference value. The number of false alarms is thereby reduced if, for example, the patient merely changes his body position, as a result of which the respiratory sound can be temporarily interrupted.

In this case, the number of time windows that are used for the final display of a hypopnea, in turn, can be varied patient-specific, which underlines the great flexibility of the inventive concept again.

In a further embodiment of the present invention, the evaluation device can be coupled to an alarm device which can perform a multiplicity of operations in the event of hypopnea. This may be, for example, alerting medical personnel or stimulating the respiration of the patient in question to immediately end the hypopnea condition. Health impairments can be avoided in this way. According to the invention, the analyzer and evaluation devices can be spatially separate from the microphone and its signal processing, the connection in particular being wireless, so that even during real-time monitoring of a sleeping patient, this component is disturbed by as few as possible components fastened to its body during sleep.

In this case, the method according to the invention can be implemented with a wide variety of techniques; in particular, this can be implemented advantageously in software that can be executed on any universal computer system. In addition, embedded solutions are conceivable that perform the process on a specialized hardware or a specially programmed FPGA, which due to its small size and low E- nergieverbrauchs also in the immediate vicinity of the microphone, that is, on the patient directly, may be appropriate.

As already mentioned above, the type of energy value determination for carrying out the method according to the invention is not fixed; for example, the energy values can also be provided with an additional weighting factor depending on their position within the time window. The relative position of the time windows, which are evaluated individually, is also not mandatory. Instead of the configuration shown in FIG. 2, in which the two time windows 34a and 34b follow one another directly, a procedure is also conceivable in which there is a time interval between two evaluated time windows which is not used for calculating the energy values. Alternatively, it is also conceivable that successive time windows overlap each other slightly over time.

Depending on the circumstances, the method according to the invention for the detection of hypopnea can be implemented in hardware or in software. The implementation can take place on a digital storage medium, in particular a floppy disc or CD with electronically readable control signals, which can cooperate with a programmable computer system in such a way that the method according to the invention for the detection of hypopnea is carried out. In general, the invention thus also consists in a computer program product with a program code stored on a machine-readable carrier for carrying out the method according to the invention when the computer program product runs on a computer. In other words, the invention can thus be realized as a computer program with a program code for carrying out the method when the computer program runs on a computer.

Claims

claims

A device for detecting hypopnea using a series of discrete samples comprising

Describe the breathing sound of a patient with the following characteristics:

an analyzer (20) for analyzing the series of samples to determine, for a number of samples corresponding to a predetermined time interval (34a, 34b) of breath noise, an energy value describing energy contained in the predetermined time interval in breath sound; and

an evaluation device (22) for detecting the occurrence of a hypopnea by comparing the energy value with a time-dependent reference value dependent on the patient.

2. Device according to claim 1, wherein the analyzer

(20) is adapted to determine the energy value as a quadratic sum of the number of samples.

Apparatus as claimed in any one of the preceding claims, wherein the analyzer (20) is adapted to analyze a series of samples corresponding to a time interval of breathing noise in the range of 100 ms to 500 ms.

4. Device according to one of the preceding claims, wherein the samples that describe the breathing sound of the patient, are determined with a sampling frequency less than 25 kHz.

5. Device according to one of the preceding claims, wherein the evaluation device (22) is formed, to detect the occurrence of hypopnea when the energy value falls below the variable reference value.

6. Device according to one of the preceding claims, wherein the evaluation device (22) is designed to calculate the variable reference value from a predetermined number of preceding energy values, which precede the energy value in time sequence.

7. The device according to claim 6, wherein the evaluation device (22) is designed to determine the variable reference value by forming the arithmetic mean of the predetermined number of preceding energy values.

8. Device according to one of the preceding claims, with the following additional features:

a microphone (24) for receiving the breath noise; and

a sampling unit for determining the series of samples based on the recording of the microphone (24).

9. Apparatus according to claim 8, wherein the microphone

(24) is a laryngeal microphone.

A device according to claim 8 or 9, wherein the scanning accuracy of the scanning unit (26) is less than 12 bits.

The apparatus of any one of claims 8 to 10, wherein the sampling unit (26) comprises a wireless data interface for transmitting the series of samples.

Apparatus as claimed in any one of the preceding claims, wherein the analyzer (20) comprises a wireless data interface for receiving the series of samples.

13. A method of detecting hypopnea using a series of discrete samples to describe a patient's breathing sound, comprising the steps of:

Analyzing the series of samples to determine, for a number of samples corresponding to a predetermined time interval of the respiratory sound, an energy value describing the energy contained within the predetermined time interval in the respiratory sound; and

Compare the energy value with a time-varying patient-dependent reference value to detect the onset of hypopnea.

14. Computer program with a program code for carrying out the method according to claim 13, when the program runs on a computer.