Abstract:
A method and device for treating snoring and obstructive sleep apnea, in which one sensor senses the onset of an episode of snoring or sleep apnea and causes production of an electrical stimulating signal consisting of a combination of direct current and a train of alternating pulses, with the respective functions of opening up restricted airway passages by stimulation of related muscle groups and eliciting a response of partial arousal, in which the condition is corrected. The onset of the episodes is sensed by an acoustic transducer, the episodes being differentiated by their unique acoustical signature by means of appropriate signal processing, the acoustical transducer also carrying one of two stimulation electrodes, which are held in light contact against the throat of the subject by means of a lightweight neckband.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the present invention relate to an apparatus for treating snoring and obstructive sleep apnea, or either of them, and also relate to a method of treatment of these conditions, using electrical stimulation. 
       BACKGROUND 
       [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 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 means of a mask connected to a pressurized air source (a technique known as Continuous Positive Airway Pressure) 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 devices and techniques belonging to this class are shown in U.S. Pat. Nos. 3,480,010 and 4,715,367 issued to Crossley; U.S. Pat. No. 3,696,377 issued to Wall; U.S. Pat. No. 4,220,142 issued to Rosen et al.; U.S. Pat. No. 4,593,686 issued to Lloyd et al.; U.S. Pat. Nos. 6,666,830 and 6,935,335 issued to Lehrman et al. and U.S. Pat. No. 6,371,120 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 Patient with Obstructive Sleep Apnea” also by Hiroshi Miki et al. U.S. Pat. No. 4,830,008 issued to Meer discusses an implantable system for treatment 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. Pat. 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 airway, 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 made evident in the writing, unidirectional pulses are effectively integrated into a direct current by storage components of capacitive and electrolytic nature intrinsic of the circuit pathway. Thus Bowman also 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 they apply to the subject will degrade the subject&#39;s sleep quality. This negates the primary objective of restoring a restful sleep to the subject. Also, subjects are deterred from using user unfriendly, cumbersome contrivances such as that proposed by Bowman. 
       SUMMARY 
       [0008]    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, comprises: 
         [0009]    a) a sensor for sensing the onset of said episode; 
         [0010]    b) a stimulus generator coupled to said sensor and responsible thereto for generating a stimulation signal for application to said person, said signal comprising a direct current and a pulsating current; 
         [0011]    c) said generator including a circuit activated upon the sensing of said episode for regulating the relative levels of said direct current and of said pulsating current as said stimulation signal is applied to said person; and 
         [0012]    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. 
         [0013]    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 comprises: 
         [0014]    a) sensing the onset of said episode; 
         [0015]    b) upon the detection of said onset, applying an electrical stimulation signal to said person, said signal comprising a direct current and a pulsating current; 
         [0016]    c) regulating the relative levels of said direct current and said pulsating current as said signal is applied to said person; 
         [0017]    d) sensing termination of said episode; and 
         [0018]    e) following sensing said termination, terminating the application of said stimulation signal to said person. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Embodiments are illustrated by way of example and without limitation in the figures of the accompanying drawings, in which like reference numerals indicate corresponding, analogous or similar elements, and in which: 
           [0020]      FIG. 1  is a plan view of the inner front part of a neck strap, which supports components of a system according to the invention; 
           [0021]      FIG. 2  is a side sectional view of an electroacoustic transducer; 
           [0022]      FIG. 3  is a block diagram of a detection circuit which detects snoring and sleep apnea episodes; and 
           [0023]      FIG. 4  is a block diagram of a stimulus generator. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Reference is made to  FIG. 1 , which is a plan view of the inner front of a neck strap  10  for use with embodiments of 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 stimulation pads  14 ,  16  in spaced apart relation, an electroacoustic transducer  18  comprising an acoustic sensing diaphragm  22  and a conductive stimulation pad  14 , and an insulating disc  20  which carries conductive stimulation pad  16 . The output of transducer  18  and conductive stimulation pads  14 ,  16  are connected to the supporting circuits for use with embodiments of the present invention by means of cable  24 . Cable  24  also carries stimulation signals to conductive stimulation pads  14  and  16 . The neck strap  10  does not need to apply more than a gentle pressure on the skin, since the stimulation circuit path is of high impedance value at the source, to minimize the effects of such variables as resistance at the pad-skin interface and others of physiological nature. 
         [0025]      FIG. 2  is a side section view of electroacoustic transducer  18 , which includes supporting structure  26  made of insulating plastic such as polycarbonate. The front of transducer  18  carries acoustic sensing diaphragm  22  made of thin polyamide foil or other material with similar mechanical electrical specifications. Diaphragm  22  is bonded at the periphery to the flat rim of supporting structure  26  and it carries conductive stimulation pad  14 , pad  14  being in the form of a disc made of thin stainless steel foil bonded to diaphragm  22  at the centre of diaphragm  22 . A thin conductive wire  30  connects pad  14  to terminal  32  on the back of the supporting structure  26 . Air cavity  38  is the site where an acoustic pressure is generated by diaphragm  22  when diaphragm  22  is vibrating in response to acoustical events such as breathing airflow and snoring, by virtue of being positioned in intimate contact with the skin of the throat. The acoustic pressure is converted into an electrical signal by microphone  34 , which is affixed with a sealing bond in a centre hole of supporting structure  26 . A shielding disc  36  is an electrostatic shield which prevents stimulation pulses present on pad  14  from interfering with the minute signal output by microphone  34 . Shielding disc  36  is mechanically supported by three or four wires  40  which have also electrically connect disc  36  to ground ring  42  which is the ground reference of the circuit. This connection further aids in making the output of microphone  34  free of interference. Terminal  44  is the output connection of microphone  34 . 
         [0026]      FIG. 3  is a block diagram of a detection circuit which detects snoring and sleep apnea episodes. In the detection circuit the signal from microphone  34  is amplified by amplifiers  50 ,  60  and then applied in two branches to bandpass filters  52 ,  62  which extract telltale signatures respectively of breathing and snoring activity. Various types of signal processing are well known to those skilled in the art to detect breathing activity and snoring activity and to filter out extraneous signal components. The snoring signal is directed to full wave rectifier  64  and then to internally referenced comparator  66 , which outputs a logic one if snoring is sensed. 
         [0027]    The breathing signal from bandpass filter  52  is rectified by full wave rectifier  54 , the output of which is directed to internally referenced comparator  56  which outputs a logic one if the acoustic signature of air flow is detected. The output of comparator  56  is used to reset a timer  58 , the output of which is set to go high after an interval of four to six seconds following any reset. Respiration cycles are typically four to six seconds and therefore the timer  58  is reset every equivalent time interval (i.e. every respiration cycle). Thus the timer  58  will output a logic one if a breathing pattern is not detected for more than six seconds. The range of four to six seconds is suggested as from experimentation this appears to be the optimal range for effective use of embodiments of the present invention. However it is not the intent of the inventor to restrict embodiments of the invention to this range, other ranges may be utilized if found to be effective. 
         [0028]    Snoring events are characterized by a logic one at the output  74  and apnea events by a logic one at output  70 . Outputs  70 ,  74  are directed to the inputs of OR gate  68 , which outputs at  72 . The information present at points  70 ,  72 ,  74  is directed to the processing circuits of the stimulus generator illustrated with reference to  FIG. 4 . 
         [0029]      FIG. 4  is a block diagram of a stimulus generator. Astable oscillator  78  is set running by a logic one at the output of OR gate  76 . The frequency of astable oscillator  78  is controlled by means of variable resistor  80  within a range of approximately three to 10 pulses per second. The output of astable oscillator  78  is directed to a Schmitt trigger  86 , via a resistor-capacitor network of capacitor  82  and variable resistor  84 , with a time constant in the range of fifty microseconds to fifty milliseconds. The output of Schmitt trigger  86  is a train of pulses with a width equivalent to the time constant of the input network. The pulse train issued by Schmitt trigger  86  is directed to level risetime control  88 , which sets the amplitude of the pulses at a pre-selected value. On one embodiment the time for pulse amplitude to reach the pre-selected value is made to be within 1 second after the sensing of a snoring event and seconds following the sensing of an apnea event, the information being supplied by apnea and snoring information present at points  70  and  74  respectively. The output of level risetime control  88  is directed to output driver  90 , which also converts the unidirectional pulses at its input into symmetrical square waves, which are then applied to the primary of step-up transformer  92 . Thus square waves with the required high voltage are present at the secondary winding of transformer  92 . 
         [0030]    HV inverter  94  raises the power source voltage to the level required for stimulation. As one skilled in the art can appreciate any number of power sources may be used to power the circuitry of embodiments of the present invention, a battery being one such example. The time for the voltage to reach a maximum value is set by DC level risetime control  96 . In one embodiment the time would be three seconds after the onset of an apnea event and zero seconds after the onset of snoring, this being accomplished by pertinent information at points  70 ,  74  applied to level risetime control  96 . Maximum level is set by DC max level control  98  which in one embodiment reduces the level by 50% if snoring information is present at point  74 . 
         [0031]    DC at the output of level control  98  is directed to polarity control unit  106  via the secondary of transformer  92 , which is connected in series in the stimulation circuit. A stimulation signal thus consists of a DC current with a square wave pulse train superimposed on it, the balance between the two modes being apt to be adjusted as required. This composite signal is directed to conductive stimulation pads  14 ,  16  via polarity control  106 , which assigns ground level and high level to either one depending on the output status of FLIP-FLOP  104  which is clocked by apnea or snoring information at point  72 . Thus the polarity applied to conductive stimulation pads  14 ,  16  is reversed at every new episode of stimulus generator operation, this being done to counteract effects of a constant polarity DC current such as electrolytic effects at the pad-skin interface and possible increase of the threshold of stimulation level. 
         [0032]    Following the onset of a snoring episode, characterized by a logic one at point  74  which starts astable oscillator  78  by means of OR gate  76 , pulse stimulation is applied to the subject with the level reaching maximum in one second, the level rise being interrupted at the point which causes the event to cease. Following the onset of a snoring episode DC stimulation is also applied to the subject, with a level reaching 50% of a pre-set maximum with no delay. DC stimulation is also interrupted at a level where the condition is interrupted. Reason for such process is that while DC stimulation acts to open the airway with a minimum of perceived effect by the subject, pulse stimulation is perceived as a tingle evoking a condition in which the event is terminated. Said perceived stimulus has the effect of conditioning the subject into subconsciously avoiding a posture conducive to snoring. The sudden application of a reduced DC level also contributes to perception. 
         [0033]    Following the onset of an apnea episode, characterized by a logic one at point  70  which activates HV inverter  94 , DC stimulation is applied to the subject, the level of which reaches a pre-selected maximum value in three seconds after the onset of the episode. Stimulation is interrupted at the level which causes the event to cease. If the episode is not corrected at maximum DC stimulation level, which is characterized by a logic one at the output of internally referenced comparator  102  and presented to one input of AND gate  108 , the other input seeing also logic one at point  70 . Therefore the output of gate  108  starts astable oscillator  78 , the end result being pulse stimulation with a level risetime of six seconds compounding the DC stimulus. 
         [0034]    The conductive stimulation pads  14 ,  16  through which the stimulation is applied have in one embodiment an active surface of one cm 2  to five cm 2  and are positioned approximately five cm to ten cm apart symmetrically to the muscle group to be stimulated. This has been found to also be an optimum area for acoustic detection of the acoustical signature of breathing, being the region of highest turbulence in the air flow, caused by restrictions which lead to or cause snoring and apnea. However, these parameters are not critical. The system is tolerant of axial offset between the stimulated region and the position of the pads, although the best results have been found if the offset is made equivalent to the spacing between the pads. 
         [0035]    While the stimulation pulses applied to the subject person may be relatively high voltage, the short duration of the pulses ensures that the overall integrated energy of each pulse is limited to values which are a fraction of a millijoule. Also, the DC stimulation current is limited to fractions of a milliamp, even if the voltages at play may be substantial by reason of a source resistance which is designed to be one order of magnitude or more higher than the combined electrical resistance of skin-pad interface and underlying tissue. The high surface area of the pads  14 ,  16  ensure that the current density at skin level be kept sufficiently low to avoid disturbing the subject person with the perception of an electric shock. 
         [0036]    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. The supporting electronics may be housed in a unit smaller than a typical cell phone, placed inside a suitable pocket of a T-shirt or other type of garment. The electrical connection to components on the neck strap is accomplished by a flexible miniature cable (Feature  24  of  FIG. 1 ) in which the conductors carry the microphone signal and stimulation current. 
         [0037]    It will be realized that various changes may be made from the preferred embodiments described. For example, separate physical sensors may be used, one to sense the onset of an episode and a different one to sense the termination of the episode. For example, the device of embodiments of the present invention may be placed on a night table or other suitable place or, with suitable miniaturization be contained on the neck strap. Functions of the device may be augmented with snoring and sleep apnea event counters. Different processing means may be used, reflecting continuous, rapid advancements in the electronic arts. The circuits described in the examples shown are examples of one implementation of embodiments of the present invention. As one skilled in the art will recognize the circuits may be created from numerous combinations of discrete components, both analog and digital. Further one skilled in the art can design circuits in other topologies to achieve the desired results. Various muscles or muscle groups may be stimulated to terminate snoring or a sleep apnea episode. Further changes may be made without departing from the scope of the present invention.