APNEA Preventive stimulating device

Abstract: The sleep-apnea syndrome is classified into a so-called central type caused by an abnormality in the respiratory center, an obstructive type by an upper airway obstruction, and a mixed type by a combination thereof. Among the rest, the obstructive type is often observed clinically and is considered to be caused by a morphological abnormality in the upper airway tract, such as tonsillar hypertrophy or micrognathia, or by a tonus of the upper airway muscle for broadening the airway. The inventors of this application have clarified by experiments that the upper airway can be recovered from obstruction which causes apnea stimulating the genioglossus, which is one of the dilator muscles of the upper airway, with pulses of a frequency of 40 to 150 Hz, a peak value of 1 to 50 volts and a rise-up time constant of 0.2 seconds or more, and that control of the start and stop of the electric stimulation with apnea detection signals would make it possible to automatically take measures to deal with apnea even at night when it is particularly difficult to find a fit of apnea.

Description: The present invention relates to an apnea preventive stimulating device for preventing the occurrence of trouble which results from abnormality in the respiratory function in one's sleep. Many studies have been reported on a so-called sleep-apnea syndrome, i.e. apnea which is accompanied by the suspension of breathing, for example, for 10 seconds or more in one's sleep at night. Such apnea in one's sleep decreases the alveolar ventilation volume and the partial pressure of arterial oxygen difference (PaO₂) and increases the partial pressure of arterial carbon dioxide (PaCO₂), and further, it lowers the chemoreceptor sensitivity and raises the upper airway resistance, thus constituting a causative factor in aggravation of the arterial blood gas. This causes pulmonary hypertension, right-sided heart failure, arrhythmia, or brain trouble, which may sometimes result in a sudden death if worst comes to worst. Thus, the breathing abnormality in one's sleep is a clinically important subject, and it is necessary to take measures for preventing the occurrence of the above-mentioned sleep-apnea. US-A-4830008 discloses a system for treatment of sleep apnea which has the features of the preamble of claim 1. It employs electrodes implanted for direct stimulation of upper airway muscles and a sensor mounted at the diaphragm. US-A-4715367 is a collar device which can be employed for treatment of snoring, bruxism and sleep apnea. Detectors and electrodes are mounted on the collar. The device employs shock aversion therapy - when an appropriate signal is detected, a mild shock is given to a motor nerve. US-A-4827935 discloses a demand electroventilator for monitoring and, when necessary, stimulating the respiration of a patient. US-A-4777963 discloses a respiration monitoring device which employs thermistor sensors mounted in each nostril and over the mouth of a patient. An object of the present invention is to provide a device effective for preventing the above-said sleep-apnea. To attain the above object of the present invention, there is provided an apnea preventive stimulating device comprising: a respiration sensing circuit having sensor means for sensing the respiration of a living patient to whom said sensor means is applied and for developing a respiration detection signal representative of the detected respiration: respiration detection signal generator means connected to said respiration sensing circuit for receiving said respiration detection signal and for producing a respiration identification signal developed only when breathing by the living patient is detected by the said sensor means; an electric stimulating wave generating circuit connected to said respiration detection signal generator means and having means for receiving said respiration identification signal including a respiration identification detector and electric stimulating wave generating means for generating electrical stimulating waves when apnea has continued for an apnea time shorter than that which could cause damage to the patient after detection of the apnea by said detection signal generator means; a stimulating circuit connected to said electric stimulating wave generating circuit and having a genioglossus stimulator to which the electrical stimulating waves are applied for genioglossus stimulation of the living patient; characterised in that said respiration sensing circuit having sensing means comprises a microphone sensor having a case positionable on the neck of the living patient to detect breath tones of the patient; the electric stimulating wave generating means starts to operate 5 to 10 seconds after an apnea is detected by the respiration detection signal generator means, and wherein the electrical stimulating waves generated by the electric stimulating wave generating means have a frequency of 40 to 100 Hz and a pulse peak value of 1 to 50 Volts; and said stimulating circuit has said genioglossus stimulator on a surface of said case of said microphone sensor. The respiration sensing circuit is formed by a microphone sensor to detect the breath tones. The intensity of the electric stimulating waves can be amplified at a predetermined time from a patient's bedtime, so that the lowering of stimulation on a patient by the electric stimulating wave during the patient's deep sleep is compensated for to wake up the patient. The sleep-apnea syndrome is classified into a so-called central type caused by an abnormality in the respiratory center, an obstructive type of an upper airway obstruction, and a mixed type by a combination thereof. Among the rest, the obstructive type is often observed clinically and is considered to be caused by a morphological abnormality in the upper airway tract, such as tonsillar hypertrophy or micrognathia, or by a tonus of the upper airway muscle for broadening the airway. The inventors of this application have clarified by experiments that the upper airway can be recovered from obstruction which causes apnea stimulating the genioglossus, which is one of the dilator muscles of the upper airway, with pulses of a frequency of 40 to 150 Hz, a peak value of 1 to 50 volts and rise-up time constant of 0.2 seconds or more, and that control of the start and stop of the electric stimulation with apnea detection signals would make it possible to automatically take measures to deal with apnea even at night when it is particularly difficult to find a fit of apnea. The present invention will be described in detail below with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram illustrating an apnea preventing stimulating device according to the present invention; Fig. 2 shows waveform diagrams explanatory of the operation of the devices described; Fig. 3A, 3B are a perspective view and section illustrating microphone sensors; Fig. 4 is a section illustrating a microphone sensor and stimulator employed in the present invention; and Fig. 5 is a schematic diagram showing positions of fixing respiration detecting sensors and the like. With reference to Fig. 1, reference character A indicates a respiration sensing circuit. A possible form of sensor in instruments of this general type is a thermistor sensor for detecting air flows from a patient's nose or mouth. Figure 2(a) actually shows an output trace from such a sensor. However, if such a sensor is used, it must be suitably connected with any necessary cords to the patient's face. This could disturb the patient's sleep and the cords could come loose accidentally. The present invention thus employs a sensor with a microphone to detect breath tones. An embodiment of such a sensor is shown in Figure 4. Sensor 11 has a sensor part 10 comprising a microphone 10a, a case 10b, a cord 10c and a sensing hole 10d. The sensor 11 also includes a stimulator 11a on the surface. A sensor 10 without stimulator 11a (as shown in Figure 3B) can be employed together with sensor 11, as shown in Figure 5. Reference numeral 2 identifies a sensor amplifier. By adjusting its amplification factor the detection sensitivity can freely be set so that a detection signal of a sufficiently high level can be obtained although the amount of respiration differs with individual patients. Reference character B denotes a respiration detection signal generator, which includes the following elements. Reference numeral 3 indicates a low-pass filter, which filters out noise signals from the low-frequency respiration detection signal available from the respiration sensing circuit A as shown in Fig. 2(b). Reference numeral 4 denotes a zero crossing comparator, which provides a train of pulses which rise and fall at the zero points when the output waveform of Fig. 2(b) rises and falls, respectively, as shown in Fig. 2(c). The pulses are level shifted as depicted in Fig. 2(d), thus producing a respiration identification signal which is not delivered during the patient's non-breathing state II. Reference character C indicates an electric stimulating wave generating circuit, which includes the following elements. Reference numeral 5 denotes a respiration identifying detector, which is formed by a retriggerable one-shot multivibrator circuit, for example, and its operation time constant is set to a value of 5 to 10 seconds which does not introduce the possibility of trouble being caused by apnea. This circuit operates in such a manner that its output is held high-level as shown in Fig. 2(e) by the successive application thereto of the pulses of Fig. 2(d) during the patient's breathing state I and and when the breathing state is altered to the non-breathing state II at a time t₁ and the respiration identification signal is no longer applied, the output still remains high until a time t₂ after a certain elapsed time, for example, 5 seconds, thereafter going low. Reference numeral 5 a denotes a start switch for test use. Reference numeral 6 indicates an electric stimulating wave generator, which is provided with a switch 6 a for manually starting its operation so that electric stimulating waves can be generated at any time for checking out the oscillation of the stimulating wave generator. A frequency setting knob 6 b is provided so that the repetition frequency of stimulation suitable to each patent can be adjusted in the range of between 40 and 150 Hz. Further, a time length setting circuit 6 c is provided, by which the generation of stimulating waves is automatically stopped when the state of apnea continues over a certain period of time and recovery from apnea can no longer be expected. In a case where the patient lapses into the non-breathing state II at the time t₁ as shown in Fig. 2(d) and the output of the one-shot multivibrator circuit 5 goes low at the time t₂ five seconds thereafter as depicted in Fig. 2(e), the electric stimulating wave generator starts to operate as shown in Fig. 2(f) and delivers electric stimulating waves as shown in Fig. 2(g). When the respiration is recovered by the stimulation at a time t₃ and the output of the one-shot multivibrator circuit 5 goes high again as depicted in Fig. 2(f), the electric stimulating wave generator stops its operation and hence stops the generation of the electric simulating waves as shown in Fig. 2(g). Reference numeral 7 indicates a stimulating wave amplifier and 7 a denotes a stimulation sensitivity adjuster, by which the amplification factor of the amplifier can be adjusted for setting its output voltage level within the range of 1 to 50 volts as desired. Reference character D identifies a stimulating circuit composed of conductive stimulating element 11a. The electric stimulating waves are applied to the genioglossus by the output of the electric stimulative wave generator 6 which is supplied to the stimulator 11a. In the embodiment shown in Fig. 1, the timer 7 b is attached to the sensitivity adjuster 7 a to amplify the intensity of the electric stimulating wave at a predetermined time (e.g. half an hour or one hour) from patient's bedtime, so that the lowering of stimulation on a patient by the electric stimulating wave during the patient's deep sleep is compensated for to wake up the patient. In this case, the amplification factor is 1.5 or 2 by way of example. Since the present invention has such a construction as described above, a patient needs only to fix the sensors and the stimulators 10 and 11 at predetermined positions before going to bed, in which case if a patient has a fit of apnea in patient's sleep, the electric stimulative wave generator 6 provides automatically stimulus to the genioglossus, which causes decreasing the obstruction of the upper airway and recovering the breathing. Thus, the present invention ensures the prevention of various diseases which are caused by the fit of apnea, and the invention achieved good results in clinical testing on patients.

Claims: An apnea preventive stimulating device comprising: a respiration sensing circuit (A) having sensor means (10,11) for sensing the respiration of a living patient to whom said sensor means (10,11) is applied and for developing a respiration detection signal representative of the detected respiration: respiration detection signal generator means (B) connected to said respiration sensing circuit for receiving said respiration detection signal and for producing a respiration identification signal developed only when breathing by the living patient is detected by the said sensor means (10,11); an electric stimulating wave generating circuit (C) connected to said respiration detection signal generator means (B) and having means for receiving said respiration identification signal including a respiration identification detector (5) and electric stimulating wave generating means (6) for generating electrical stimulating waves when apnea has continued for an apnea time shorter than that which could cause damage to the patient after detection of the apnea by said detection signal generator means (B); a stimulating circuit (D) connected to said electric stimulating wave generating circuit (C) and having a genioglossus stimulator (8,9,11a) to which the electrical stimulating waves are applied for genioglossus stimulation of the living patient; characterised in that said respiration sensing circuit (A) having sensing means (11) comprises a microphone sensor (10a) having a case (10b) positionable on the neck of the living patient to detect breath tones of the patient; the electric stimulating wave generating means (6) starts to operate 5 to 10 seconds after an apnea is detected by the respiration detection signal generator means (B), and wherein the electrical stimulating waves generated by the electric stimulating wave generating means (6) have a frequency of 40 to 100 Hz and a pulse peak value of 1 to 50 Volts; and said stimulating circuit (D) has said genioglossus stimulator (11a) on a surface of said case (10b) of said microphone sensor (10a). An apnea preventive stimulating device according to claim 1, characterised in that said electric stimulating wave generating circuit (C) comprises control means including an amplifier (7) for controlling intensity of the electric stimulating waves at a predetermined time from the living patient's bedtime; and said control means comprises a sensitive adjuster (7a) coupled with said amplifier to lower and to amplify the intensity of the electric stimulating waves and a timer (7b) connected to said sensitive adjuster so that lowering of stimulation on the living patient by the electric stimulating waves during deep sleep of the living patient is effectively compensated for to wake up the living patient.

Inventors: HIDA WATARU, MIKI HIROSHI, TAKISHIMA TAMOTSU, HIDA, WATARU, MIKI, HIROSHI, TAKISHIMA, TAMOTSU
Applicants: CHEST CORP, CHEST CORPORATION
Application year: 1990
Main classification: A61N1
IPC codes: A61N1, A61B5