WO2007140584A1

WO2007140584A1 - Method and apparatus for treating sleep apnea and snoring

Info

Publication number: WO2007140584A1
Application number: PCT/CA2007/000966
Authority: WO
Inventors: William Toderan; Franco Villa
Original assignee: William Toderan; Franco Villa
Priority date: 2006-06-02
Filing date: 2007-05-31
Publication date: 2007-12-13

Abstract

A method and device for treating snoring and obstructive sleep apnea, in which one or more sensors sense the onset of an episode of snoring or sleep apnea and cause production of an electrical stimulation signal consisting of a train of alternating pulses. The pulse intensity is ramped up from a low level to a level high enough to end the episode. The end of the episode is sensed and the stimulation signal is then ramped down or turned off. Therefore, while the intensity of the stimulation signal has become high enough to end the undesired episode, the intensity does not become higher than that needed for this purpose. Therefore, the stimulation signal is less likely to disturb the sleep of the person being treated.

Description

Title: METHOD AND APPARATUS FOR TREATING SLEEP APNEA AND

SNORING

Field of the invention

[0001] This invention relates to apparatus for treating snoring and obstructive sleep apnea, or either of them, and also relates to a method of treatment of these conditions, using electrical stimulation. Background of the invention

[0002] Snoring is a condition commonly caused by a partial obstruction of the upper airway, in which the airflow causes the obstructing tissue to resonate, resulting in characteristic and well-known snoring sounds. Snoring can be a major disruptive agent in relationships where one person is subjected to the sleep disturbing effects which the snoring partner causes.

[0003] Obstructive sleep apnea is a more serious medical condition caused by a more pronounced obstruction such that the airflow during breathing is severely restricted or is completely interrupted. This condition causes a degraded sleep pattern and reduced blood oxygenation and is believed to have the potential for producing serious medical problems, including cardiovascular complications.

[0004] Various solutions are well-known for treating upper airway obstructions. Some of these solutions involve an insertion of mechanical devices, or even surgical interventions. Subjecting the airway to a constant pressure of a few millibars by a mask connected to a pressurized air source (a technique known as CPAP) is a proven method of controlling sleep apnea. However, these techniques are invasive and therefore persons are reluctant to use them.

[0005] Other less invasive techniques are known, in which the onset of the obstructive condition is detected and a stimulus is applied to disturb the person, in order to elicit a response in which the condition is corrected. Examples of inventions belonging to this class are shown in U.S. Patents Nos. 3,480,010 and 4,715,367 issued to Crossley; U.S. Patent No. 3,696,377 issued to Wall; U.S. Patent No. 3,998,209 issued to Macvaugh; U.S. Patent No. 4,220,142 issued to Rosen et al.; U.S. Patent No. 4,593,686 issued to Lloyd et al.; U.S. Patent No. 6,666, 830B1 and 6,935, 335B1 issued to Lehrman et al. and U.S. Patent No. 6,371 ,120B1 issued to Chiu et al. These devices operate by a variety of techniques which have in common two aspects: firstly, detection of the obstructed airway condition (either snoring or sleep apnea), and secondly, applying a stimulus to the subject in respect to such detection.

[0006] Recent research has shown that obstructions in upper airways may be cleared with electrical stimulation. Two articles describing this research may be found in American Review of Respiratory Disease, Vol. 140, 1989 at pp. 1279-1289. The first article is entitled "Effects of Electrical Stimulation of the Genioglossus on Upper Airway Resistance in Anesthetized Dogs" by Hiroshi Miki et al. The second article is entitled "Effects of Submental Electrical Stimulation During Sleep on Upper Airway Patency in Patients with Obstructive Sleep Apnea". U.S. Patent No. 4,830,008 issued to Meer discusses an implantable system for treatment of obstructive sleep apnea by means of electrical stimulation. A system achieving the same goal by the same means without resorting to implantation is discussed in U.S. Patent No. 5,265,624 issued to Bowman. In this system, electrodes are placed on the gums, thus in the immediate vicinity of the genioglossus and related muscle groups in the upper airways, by means of a mouthpiece fitted with passive circuitry energized by radio frequency emitted by a collar assembly which incorporates the power supply and event detector. Radio frequency is processed within the mouthpiece in order to power the circuit and issue a train of narrow unidirectional pulses to the stimulating electrodes. Although not evident from the writing, unidirectional pulses are effectively integrated (or rectified) into a direct current by storage components of capacitive and electrolytic nature intrinsic in the circuit pathway. Thus Bowman relies on DC stimulation of the muscles of interest. [0007] A disadvantage of the prior art devices is that there is a substantial likelihood that the stimulus which they apply to the subject will degrade the subject's sleep quality. This negates the primary objective of restoring a restful sleep to the subject. Brief summary of the invention

[0008] In one aspect the invention provides an apparatus for treating an obstruction of the upper airway of a person, such condition causing an episode of either snoring or obstructive sleep apnea, said apparatus comprising: a) a sensor for sensing the onset of a said episode, b) a stimulation signal generator coupled to said sensor and responsive thereto for generating a stimulation signal for application to said person, said stimulation signal comprising a series of pulses, c) said generator including a ramping device for initiating the generation of said stimulation signal at a selected intensity and then for increasing said intensity with time as said stimulation signal is applied to said person, d) a sensor for detecting the end of said episode and being coupled to said generator for terminating the application of said stimulation signal to said person following the end of said episode.

[0009] In another aspect the invention provides a method of treating a person having an obstruction of the upper airway causing the onset of either a snoring or an obstructive sleep apnea episode, comprising:

a) sensing the onset of a said episode,

b) upon the detection of said onset, applying an electrical stimulation signal to said person,

c) increasing the intensity of said stimulation signal with time as said stimulation signal is applied to said person,

d) sensing the termination of said episode, e) following sensing said termination, terminating the application of said stimulation signal to said person.

[0010] Further aspects and advantages of the invention will appear from the following description, taken together with the accompanying drawings.

Brief description of the drawings [0011] In the drawings:

[0012] Fig. 1 is a plan view of the front part of a neck strap which supports components of a system according to the invention; [0013] Fig. 2 is a block diagram of the detection part of a circuit for the

Fig. 1 system;

[0014] Fig. 3 is a block diagram of a pulse generating and shaping part of the Fig. 1 system;

[0015] Fig. 4 is a plan view of the front part of a chest strap housing components of a system according to the invention;

[0016] Fig. 5 is a block diagram of the detection part of the circuit of the

Fig. 4 system; and

[0017] Fig. 6 is a block diagram of the pulse generating and shaping part of the circuit of the Fig. 4 system. Detailed description of preferred embodiments

[0018] Reference is first made to Fig. 1 , which is a plan view of a neck strap 10 for use with the present invention. The neck strap 10 includes a main substrate 12 of woven material with a sufficiently open weave to allow for evaporation of skin moisture. The neck strap 10 supports conductive pads 14, 16 in spaced apart relation, a microphone 18, a battery 20, and an electronic circuit module 22 with a slide power switch 24 on one side of the module. The neck strap 10 does not need to apply more than a gentle pressure on the skin, since voltages may be used which are sufficiently elevated to overcome high resistivity in the pad-to-skin contacts. [0019] Fig. 2 is a block diagram of a detection circuit 30 which forms part of the circuit module 22. The detection circuit 30 detects snoring and sleep apnea episodes. In the detection circuit 30, signal from the microphone 18 is amplified by an amplifier 32 and is then applied in two branches to bandpass filters 34, 36 which extract telltale signatures respectively of snoring and breathing activity. Various types of signal processing are well-known to those skilled in the art to detect snoring activity and breathing activity and to filter out extraneous signal components. The snoring signal is directed to full wave rectifier 38 and then to internally referenced comparator 40, which outputs a logic one if snoring is sensed.

[0020] The breathing signal from bandpass filter 36 is rectified by full wave rectifier 44, the output of which is directed to internally referenced comparator 46 which outputs logic one if the acoustic signature of airflow is detected. The output of the comparator 46 is used to reset a timer 48, the output of which is set to go high after an interval of 4-6 seconds following any reset. Respiration cycles are typically 4-6 seconds, and therefore the timer 48 is reset every equivalent time interval (i.e. every respiration cycle). Thus, the timer 48 will output a logic one signal if a breathing pattern is not detected for more than six seconds. [0021] Snoring and apnea events, characterized by output high or logic one from the comparator 46 and the timer 48 are directed to the inputs of OR gate 54, which outputs a signal at terminal 56 for a pulse generator (to be described) to initiate stimulation of the subject person.

[0022] Fig. 3 is a block diagram of the pulse generating and shaping part 58 of the electronic circuit module 22. Information to initiate stimulation, namely, a logic one signal at terminal 56, sets astable oscillator 60 running and generating a square wave 62 with a pulse repetition rate of 3-10 pulses per second. The square wave 62 is applied to a Schmitt inverter 64 via an RC network of capacitor 70 and resistor 72, with a time constant ranging preferably between 40 microseconds and 200 milliseconds. The output of inverter 64 is a square wave pulse train 74 with pulse width equivalent to the time constant of the input network. The pulse train 74 is directed to the input of another Schmitt inverter 76 which inverts the phase of its input pulses and outputs a pulse train 78. The two phases 74, 78 are applied to photo MOS network 80 to process the high voltage applied to the network at connection 82 (as will be described).

[0023] The logic one signal at terminal 56 is also applied to a capacitor

84 through a resistor 86, the values of these components being chosen so that a time constant of 3-6 seconds is achieved. The rising voltage at capacitor 84 is applied to the negative input of a comparator 90, the output of which is directed to control the start-stop mode of a high voltage inverter 92, which runs when its control is at logic zero. When inverter 92 is operational, its output is rectified by diode 94 and is stored in capacitor 96 which may typically have a value of 0.22 microfarad. The resultant DC high voltage at terminal 82 is presented to photo MOS switches 80, which output pulses of alternating polarity having the frequency and width of the controlling pulses from Schmitt inverters 64, 76 and having the amplitude of the input DC high voltage at terminal 82. The outputs 98 of the switches 80 are connected to the stimulating pads 14, 16.

[0024] High voltage at terminal 82 is also connected to a voltage divider consisting of resistors 100, 102. The output terminal 104 of the voltage divider is connected to the positive input of comparator 90, thus forming a feedback circuit. This feedback circuit will lock the value of the high voltage at terminal 82 to that of the voltage at capacitor 84, with the relationship of 1 to

1. Thus, at the onset of a logic one signal (typically 3 volts) at terminal 56, the high voltage at terminal 82 will increase from zero to 300 volts following the time constant of resistor 72 and capacitor 70. If the logic one signal at terminal 56 becomes zero, following correction of the snoring or sleep apnea condition, then the voltage at terminal 56 will decrease to zero as a result of discharge of capacitor 84 through resistor 86, thus decreasing and then terminating the stimulation signal applied to the subject person. [0025] It will therefore be seen that upon the onset of a snoring or sleep apnea condition, stimulation pulses are applied to the subject with an amplitude which progressively increases, e.g. at a rate of between 20 volts per second and 50 volts per second, starting from a baseline which can be zero or any preselected value above zero, to a level which causes the apnea or snoring event to cease. At this point, the detection circuit 30 outputs a logic zero and the stimulation signal is interrupted (by ceasing to rise, and instead decreasing), thus minimizing the disturbance to the subject person's sleep.

[0026] The conductive pads 14, 16 through which the stimulation is applied preferably each have an active surface area of 1-5 cm² and are preferably positioned approximately 5-10 cm apart symmetrically to the muscle group to be stimulated. However, these parameters are not critical.

The system is tolerant of axial offset between the stimulated region and the position of the pads, although preferably the offset is made equivalent to the spacing between the pads.

[0027] While the stimulation pulses applied to the subject person may be of relatively high voltage, the short duration of the pulses ensures that the overall integrated energy of each pulse is limited to values that are a fraction of a millijoule. The high surface area of the pads 14, 16 ensures that the current density at skin level will be kept sufficiently low to avoid disturbing the subject person with the perception of an electric shock.

[0028] Since the stimulation pulses are of alternating polarity, they will not cause electrolytic polarization in the subject person's tissue, which would gradually desensitize the subject person's physiological response to the stimulus.

[0029] The neck strap 10 may be fastened by any desired means, e.g. hook and loop pads (not shown) attached to the ends of the strap.

[0030] As an alternative, the components described may be attached to a chest strap 10' as shown in Fig. 4, the chest strap 10' being fastened (by any desired means) around the chest of the subject. (In Figs. 4 to 6, primed reference numerals indicate parts corresponding to those of Figs. 1-3.) Again, the main substrate 12' of the chest strap is preferably a woven material with sufficiently open weave to allow skin moisture to evaporate. The center portion 112 of the chest strap may be of stretchable material, to allow for mechanical loading of a strain gauge 112 which is preferably connected to the non-stretchable material at 114, at each side of the stretchable patch 110.

[0031] Unlike the Fig. 1 embodiment, where the same microphone 18 is used for detection of both snoring and sleep apnea conditions, in the Fig. 4 embodiment only snoring is detected by the microphone 18. The presence or absence of breathing is detected by strain gauge 112 in response to chest movements. The output of strain gauge 112 is sent directly to the positive input of comparator 44' shown in Fig. 5. The negative input of the comparator 44' is connected to an integrating network of resistor 116 and capacitor 118 having a time constant of 120 seconds. The output of this network supplies the comparator 44' with a baseline reference which tracks variations in the mechanical bias of the strain gauge 112.

[0032] As before, the output of the comparator 44' resets timer 48', the output of which becomes high six seconds following reset, thus outputting a logic one signal if inhalation does not occur for more than six seconds. The output of timer 48" is connected to one input of AND gate 120 and the other input 122 is connected to the output of another timer 124, which outputs a logic one signal 120 seconds following circuit power-up.

[0033] This arrangement disables apnea sensing for the initial 120 seconds after circuit power up, in order for baseline reference at capacitor 118 to stabilize. After the initial delay, a breathing interruption of more than six seconds will cause the output of AND gate 120 to be high. Circuit and sleep apnea information are thus present at terminal 56', at the output of OR gate 54'.

[0034] Fig. 5 is the part of the circuit which generates and shapes stimulation pulses for application to the subject person and is identical to the circuit of Fig. 3 except for the use of primed reference numerals. [0035] It will be realized that various changes may be made from the preferred embodiments described. For example, the device of the invention may be attached to an appropriate garment, such as a t-shirt. Different processing means may be used, e.g. appropriate integrated logic chips in place of the discrete circuit components shown. Various muscles or muscle groups may be stimulated to terminate snoring or a sleep apnea episode. The stimulation signal applied may, when the snoring or sleep apnea episode has ended, be decreased to zero or a low level over a short time (as described), or it may be rapidly totally switched off. Further changes may be made without departing from the scope of the present invention.

Claims

Claims:

1. Apparatus for treating an obstruction of the upper airway of a person, such condition causing an episode of either snoring or obstructive sleep apnea, said apparatus comprising: a) a sensor for sensing the onset of a said episode, b) a stimulation signal generator coupled to said sensor and responsive thereto for generating a stimulation signal for application to said person, said signal comprising a series of pulses, c) said generator including a ramping device for initiating the generation of said stimulation signal at a selected intensity and then for increasing said intensity with time as said stimulation signal is applied to said person, d) a sensor for detecting the end of said episode and being coupled to said generator for terminating the application of said stimulation signal to said person following the end of said episode.

2. Apparatus according to claim 1 in which the same sensor is used for detecting the onset of said episode and the end of said episode.

3. Apparatus according to claim 1 wherein said pulses are square wave pulses.

4. Apparatus according to claim 3 wherein said pulses have alternating electrical polarity.

5. Apparatus according to claim 4 wherein said generator produces said alternating polarity pulses with a pulse repetition rate of between 3 and 10 pulses per second.

6. Apparatus according to claim 5 wherein said generator produces said pulses with a pulse width between 50 microseconds and 200 milliseconds.

7. Apparatus according to claim 6 wherein the intensity of said stimulation signal is increased by said generator increasing the amplitude of said pulses from a selected base level to a value of approximately 300 volts.

8. Apparatus according to claim 7 wherein said generator increases the amplitude of said pulses at a rate of between 20 and 50 volts per second.

9. A method of treating a person having an obstruction of the upper airway causing the onset of either a snoring or an obstructive sleep apnea episode, comprising:

a) sensing the onset of a said episode,

d) sensing the termination of said episode,

e) following sensing said termination, terminating the application of said stimulation signal to said person.

10. A method according to claim 9 wherein the step of terminating the application of said stimulation signal to said person comprises decreasing over time the intensity of the stimulation signal applied to said person.

11. A method according to claim 9 wherein said stimulation signal comprises a series of pulses.

12. A method according to claim 11 wherein said pulses are square wave pulses.

13. A method according to claim 12 wherein said pulses have alternating electrical polarity.