RESPIRATION MONITOR
United States Patent 3831586
A respiration monitor comprising a sensing unit which senses the expansion and contraction of the chest, abdomen, side or back; and through the electrical system sounds an alarm if this motion ceases. The respiration motion is changed to an electrical signal in the transducer. Two points on the skin surface are selected as reference points and the relative motion of the two points is monitored by a light modulation method. A small transducer is mounted on the skin at the first reference point. A thin and flexible modulation reed which conforms to the curvature of the body is mounted at the second reference point, and extends through a slot in the transducer. The relative motion of the modulation reed with reference to the transducer causes the light intensity impinging on a sensor to change thereby changing the sensor's resistance and whenever light modulation stops, the electronic circuitry produces a visual or audial alarm and the patient is attended.
US Patent References:
Mattress alarm
Farris - June 1967 - 3325799
Respiration monitor
Kohrer - October 1967 - 3347222
BREATHING ACTIVITY MONITORING AND ALARM DEVICE
Alter - June 1970 - 3658052
Mattress alarm
Farris - June 1967 - 3325799
Respiration monitor
Kohrer - October 1967 - 3347222
BREATHING ACTIVITY MONITORING AND ALARM DEVICE
Alter - June 1970 - 3658052
Application Number:
05/307091
Publication Date:
08/27/1974
Filing Date:
11/16/1972
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
5/940, 338/47, 340/573.100, 310/330
International Classes:
A61B5/113; A61B5/11; A61B5/02
Field of Search:
340/279 128/2R,2S,DIG.17,2.5V,2.5E,2.08
Other References:
IB.M. Technical Disclosure Bulletin page 13, Vol. 6, No. 6, November 1963..
Primary Examiner:
Medbery, Aldrich F.
Attorney, Agent or Firm:
Henry, Patrick F.
Claims:
What is claimed is
1. In a respiration monitor for use on a person including application to an infant to monitor breathing:
2. The device in claim 1: said light modifying member being a reed-like member having one end attached to the person and the other end moving to interrupt the light.
3. The device in claim 1: wherein said circuit includes electrical means for responding to a change in voltage caused by the change in light on the light responsive element and means for delaying for a period of time before actuating the alarm whereby temporary pauses with resumption of normal breathing do not actuate the alarm.
4. The device in claim 1 wherein said light sensitive component is a photo-resistor.
5. The device in claim 1, wherein: said light is a light emitting diode.
6. The device is claim 1 wherein said light sensitive component as a photo-transistor.
7. The device in claim 1 wherein said light sensitive component is a photo-darlington unit.
8. The device in claim 1 wherein said light is a minature incandescent lamp.
9. The device in claim 1 wherein said light is a fiber optic light source.
1. In a respiration monitor for use on a person including application to an infant to monitor breathing:
2. The device in claim 1: said light modifying member being a reed-like member having one end attached to the person and the other end moving to interrupt the light.
3. The device in claim 1: wherein said circuit includes electrical means for responding to a change in voltage caused by the change in light on the light responsive element and means for delaying for a period of time before actuating the alarm whereby temporary pauses with resumption of normal breathing do not actuate the alarm.
4. The device in claim 1 wherein said light sensitive component is a photo-resistor.
5. The device in claim 1, wherein: said light is a light emitting diode.
6. The device is claim 1 wherein said light sensitive component as a photo-transistor.
7. The device in claim 1 wherein said light sensitive component is a photo-darlington unit.
8. The device in claim 1 wherein said light is a minature incandescent lamp.
9. The device in claim 1 wherein said light is a fiber optic light source.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Medical monitoring methods and devices and especially respiration monitoring apparatus. U.S. Class 128 Subclass 2.05 or International Class A61b5/02. Transducer montioring devices for sensing physiological changes: Class 310 subclass 8.5; Class 338 Subclass 47.
2. Description of the Prior Art
The following patents are noted:
3,268,845 2,829,637 2,854,968 3,508,235 3,258,009 2,699,465 3,325,799 3,082,414 3,154,066 3,387,149 1,619,005 3,483,861 3,097,639 3,348,535 1,282,908 2,848,992 3,090,377 3,513,832 2,452,799 3,442,263 3,313,803 2,828,734 2,368,207 3,474,526 3,163,856 2,702,354 1,619,886
As disclosed by the above noted prior art there are many respiration monitors published and some of which are currently available. These include respiration and movement transducers disclosed in U.S. Pat. No. 3,268,845. The ones that are at all suitable for premature infants and the like are primarily designed for use on premature infants who are subject to sudden inexplicable cessation of respiration (apnea attack). These attacks generally occur without any warning. Others of these respiration monitors are designed for use in the intensive care units of hospitals and most of these require the bonding of electrodes to the body which is a source of numerous problems because the conductive jelly irritates the skin and those that do not utilize conductive jelly are bulky and taped in place or are not sensitive enough to monitor small prematures and slight changes. All of these devices are very complex electronically and consequently the costs are correspondingly high. Also, many of these include problems of AC current grounding and leakage and electromotive force dropping across the patient. To summarize the situation, the currently available monitors are so complex that the expense precludes their use in many instances where they are required and needed. Most hospitals can only afford a few units whereas the need for these monitors is many times this number. The present invention solves the problems of cost by means of an inexpensive respiratory monitor which is simple to operate but at the same time is rugged, reliable and more sensitive than previous models thereby solving the problem of sensitivity but without the use of conductive jellies and bulkiness. The present unit is so inexpensive and simple to operate that it can be used by non-medically trained personnel thereby solving the problem of complex electronics and the use of electronically trained technicians. The electronics in the present system is so simple and dependable as to provide a very low current drain feasible for use with a dry or wet cell battery for power, eliminating the possibility of electrical shocks and the failure of the unit from loss of outside power and the more complex arrangement of standby battery power to take over in the case of AC failure. The problem of patient contact is solved by the present invention through the use of a universal transducer which does not have to come in direct contact with the subject in order to measure respiration or movement. The transducer can be attached to the patient in a variety of ways and placed in a variety of positions on the body. Therefore, the present invention unlike the prior art devices provides a novel means of attaching a transducer to the patient so as to minimize discomfort, false signals, ease of application and reliability.
SUMMARY OF THE INVENTION
The present unit comprises the respiratory movement sensing apparatus, which comprises a light modulation transducer and modulation reed and the means of attaching said transducer and reed to the patient via a small rubber belt or adhesive pad, and an electronic unit which monitors the transducer signal and gives a light and audible alarm when respiration ceases for an adjustable time ranging from 6 to 30 =l seconds.
Other and further objects and advantages of this invention will be apparent from reading the description of the preferred embodiment in conjunction with the drawings as follows:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an infant with the reed and transducer unit mounted across the chest and abdomen and with a portion of a typical incubator shown in dotted lines. The electronics unit is also shown.
FIG. 2 is a cross-sectional view taken on line 2--2 of FIG. 8 of the direct modulation method of sensing respiratory movement whereby the light source shines through the modulation reed onto the sensor.
FIG. 3 is an alternate indirect modulation method whereby light is reflected from a surface behind the reed onto the sensor.
FIG. 4 is a perspective view of a portion of the belt.
FIG. 5 is a top plan view of the belt shown in FIG. 4 with the transducer and modulation reed mounted thereon.
FIG. 6 is a perspective view of a detail of the adhesive disposable used as an alternative means of mounting the transducer and reed.
FIG. 7 is a top plan view of the transducer and reed attached with the adhesive disposable pads.
FIG. 8 is a side elevation view of the transducer and light sensing housing with the belt shown in dotted lines.
FIG. 9 is a cross-sectional view of another modulation reed.
FIG. 10 is a schematic circuit diagram of the sensing electronics system.
FIG. 11 is a diagrammatic view of the sensing unit mounted longitudinally on the upper abdomen and chest.
FIG. 12 is a diagrammatic view with the sensing unit mounted transversely on the abdomen.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
The motion sensing unit is mounted on the back, front or side of the patient as shown in FIGS. 11 and 12 and is comprised of the modulation reed 46 and grid 60 and the transducer 14. The internal details of the transducer are shown in FIGS. 2 and 3. The transducer housing 16 to which is attached an electrical wire 18 leading to the transducer is shown in FIG. 8. The housing 16 contains the light sensor 20 which converts light energy to electrical energy, which is well known in the art, and is activated by means of a small focused light source 22, which is also mounted in the housing 16. The relative motion of two points on the skin surface is monitored by a unique light modulation technique. The relative motion of the grid 60 on the modulation reed 46 in the transducer slot 28 causes the light intensity impinging on the sensor to change thus changing the sensors resistance (resistor) or turning it on and off (transistor). This can be accomplished either by a direct modulation technique whereby the light is shined through the reed onto the sensor (FIG. 2) or by an indirect modulation technique whereby light is reflected from a surface behind the reed (FIG. 3). The sensitivity of the transducer can be adjusted by changing the width of the modulation bars (grid) on the reed and the width of the sensor aperature and by changing the intensity and type of light source and the type of sensor.
As shown in FIGS. 4 and 5, the mounting belt 30 comprises a pair of pockets 40 in which are mounted the transducer 14 and modulation reed 46. The transducer is mounted by means of a tongue formed by the bottom portion 26 of the housing 16, and the reed is mounted by means of a slotted tongue 44 on the reed arrangement 46. The reed 46 includes an elongated connection member 48 which contains the modulation medium or grid 60. The motion sensing unit can also be mounted by adhesive mounting pads 52 which have pockets 40' for mounting the transducer or reed.
The grid 60 of the modulation reed can either be perforated to allow the passage of light, or be a clear plastic with an opaque set of bars or circular discs. The reed material must be thin and flexible to allow it to conform to the curvature of the body between the transducer and the reed mounting point without causing excess friction in the slot 28 on the transducer.
The transducer housing 16 and the reed 46 are attached to the patient by the belt 30 but they also may be attached by means of disposable adhesive (FIG. 6) or any other suitable method which allows the reed 46 to move relative to the slot in the transducer as respiration occurs. The transducer housing 16 and reed 46 are preferably placed in the position where the relative motion between the two attachment points is at least 0.5 mm so that the transducer will translate the signal. If the transducer housing 16 and reed 46 are attached with the disposable adhesive, there are many positions and alignments of the body which will provide for satisfactory monitoring even on the smallest premature infant with very shallow breathing pattern. Some infants have most respiratory motion occurring between the upper abdomen 54 and the lower rib cage 56. In this case, the transducer housing 16 and reed 46 can best be mounted so that the reed 46 is aligned with the length of the body (See FIG. 11). The transducer housing 16 is mounted on the upper abdomen 54 above the navel 58 and the reed is attached to the chest 56 above the transducer. Other infants have more motion occurring from the expansion of the diameter of the abdomen 54 and in this case the transducer housing 16 and reed 46 should be mounted from left to right and perpendicular to the actions of the body on the upper abdomen 54 as shown in FIG. 12. If the rubber belt 30 is used, it can be placed around the abdomen 54 either above or below the navel 58. The transducer housing 16 and reed 46 can be placed either on the abdomen or back of the patient.
The alignment of the reed 46 and the transducer housing 16 is not so critical due to the shape of the reed slot 44 shown in FIG. 9. The "hourglass" shape allows misalignments of up to 30° before the reed 46 binds in the slot. The reed 46 is only wide enough to cover the sensor aperture while in contact with one wall of the aperture. The sensor aperture 24 is square to increase sensitivity.
DESCRIPTION OF THE ELECTRONIC CIRCUIT FIG. 10 (Example)
Basically the circuit disclosed in FIG. 10 detects modulated light from the transducer to the circuit and includes resistors R1 through R 17; transistors Q1 thru Q7; capacitors C1 and C2; switch S1. When light modulation ceases for a period of 6 to 30 seconds (adjustment is made by changing the value of R11) an alarm B is sounded. Changes in light intensity are detected by the photoresistor PR as shown or by any other suitable device such as a photo-transistor or photo-darlington. These light changes result in a voltage change across resistor R2. The FET (abbreviation for unipoler field effect transistor) Q1 provides the needed impedance conversion between R2 and the input Q2. However, the signal from R2 is not amplified by Q1. The capacitor C1 isolates the D.C. voltage bias to the input of Q2. R5 serves as a sensitivity adjustment. The transistors Q2 and Q3 operate as a unit to provide high amplification. In fact, in this application transistors Q2 and Q3 saturate at approximately 4.5 volts in the presence of the input signal across R5. Therefore, the voltage from the input side of R10 to ground is either 0 volts in the absence of light modulation or 4.5 volts when light is being modulated. Q4 operates as a switch, which is on when the voltage across R10 is high. When Q4 is turned on, a charging current is supplied to the capacitor C2. The voltage across C2 increases turning on transistor Q6, this lowers the voltage at the input of R15 and turns off Q7. In this state the audio alarm B is silent. However, when light modulation stops, the voltage across C2 decreases slowly providing a time delay controlled by R11. When C2 is discharged the voltage at the input of Q7 is high and Q7 conducts thereby turning on the audio alarm B.
The indicator light L provides a visual indication as to the state of the system. This light L is controlled by a darlington transistor pair Q5. When switch S1 is placed in the test position the indicator light L burns intermittently or constantly depending on the respiration rate when the transducer T is being modulated, i.e., a normal condition exists. However, when the switch S1 is switched in the ON, the light L is turned off and only burns when the audio alarm is sounding, i.e., respiration ceases.
The L.E.D. (light emitting diode) CRI is located remotely in the transducer T, and provides the light source for the photo-resistor PR which is also remotely located in the transducer T.
This device is inherently fail-safe to the discharge of the battery. As the supply voltage decreases, the system sensitivity decreases. When the sensitivity has decreased sufficiently the system will react, as if a patient respiration failure had occurred and the audio alarm B will be sounded. Low battery voltage may then be verified by observing the battery level indicator also.
SUMMARY OF OPERATION OF DEVICE
The rhythmic breathing of the patient causes the static or passive condition of the system, that is, as long as the light from the light emitting diode L.E.D. is broken regularly and rhymically by the "shutter" 32 of the reed 46, the voltage changes occur across the photo-resistor and these changes are amplified and utlilized to keep the alarm clock deactivated. When breathing stops for a period of time (e.g. 6 to 30 seconds) the change in the intensity light impinging on PR ceases and the Alarm B is sounded after the preset time delay.
While I have shown and described a preferred embodiment of my invention with suggested modifications, this is by way of illustration only and does not constitute any sort of restriction thereon, since there are various alterations, changes, deviations, departures, omissions, additions, and variations which may be made in the disclosed invention without departing therefrom as determined only by reference to a proper construction of the appended claims.
1. Field of the Invention
Medical monitoring methods and devices and especially respiration monitoring apparatus. U.S. Class 128 Subclass 2.05 or International Class A61b5/02. Transducer montioring devices for sensing physiological changes: Class 310 subclass 8.5; Class 338 Subclass 47.
2. Description of the Prior Art
The following patents are noted:
3,268,845 2,829,637 2,854,968 3,508,235 3,258,009 2,699,465 3,325,799 3,082,414 3,154,066 3,387,149 1,619,005 3,483,861 3,097,639 3,348,535 1,282,908 2,848,992 3,090,377 3,513,832 2,452,799 3,442,263 3,313,803 2,828,734 2,368,207 3,474,526 3,163,856 2,702,354 1,619,886
As disclosed by the above noted prior art there are many respiration monitors published and some of which are currently available. These include respiration and movement transducers disclosed in U.S. Pat. No. 3,268,845. The ones that are at all suitable for premature infants and the like are primarily designed for use on premature infants who are subject to sudden inexplicable cessation of respiration (apnea attack). These attacks generally occur without any warning. Others of these respiration monitors are designed for use in the intensive care units of hospitals and most of these require the bonding of electrodes to the body which is a source of numerous problems because the conductive jelly irritates the skin and those that do not utilize conductive jelly are bulky and taped in place or are not sensitive enough to monitor small prematures and slight changes. All of these devices are very complex electronically and consequently the costs are correspondingly high. Also, many of these include problems of AC current grounding and leakage and electromotive force dropping across the patient. To summarize the situation, the currently available monitors are so complex that the expense precludes their use in many instances where they are required and needed. Most hospitals can only afford a few units whereas the need for these monitors is many times this number. The present invention solves the problems of cost by means of an inexpensive respiratory monitor which is simple to operate but at the same time is rugged, reliable and more sensitive than previous models thereby solving the problem of sensitivity but without the use of conductive jellies and bulkiness. The present unit is so inexpensive and simple to operate that it can be used by non-medically trained personnel thereby solving the problem of complex electronics and the use of electronically trained technicians. The electronics in the present system is so simple and dependable as to provide a very low current drain feasible for use with a dry or wet cell battery for power, eliminating the possibility of electrical shocks and the failure of the unit from loss of outside power and the more complex arrangement of standby battery power to take over in the case of AC failure. The problem of patient contact is solved by the present invention through the use of a universal transducer which does not have to come in direct contact with the subject in order to measure respiration or movement. The transducer can be attached to the patient in a variety of ways and placed in a variety of positions on the body. Therefore, the present invention unlike the prior art devices provides a novel means of attaching a transducer to the patient so as to minimize discomfort, false signals, ease of application and reliability.
SUMMARY OF THE INVENTION
The present unit comprises the respiratory movement sensing apparatus, which comprises a light modulation transducer and modulation reed and the means of attaching said transducer and reed to the patient via a small rubber belt or adhesive pad, and an electronic unit which monitors the transducer signal and gives a light and audible alarm when respiration ceases for an adjustable time ranging from 6 to 30 =l seconds.
Other and further objects and advantages of this invention will be apparent from reading the description of the preferred embodiment in conjunction with the drawings as follows:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an infant with the reed and transducer unit mounted across the chest and abdomen and with a portion of a typical incubator shown in dotted lines. The electronics unit is also shown.
FIG. 2 is a cross-sectional view taken on line 2--2 of FIG. 8 of the direct modulation method of sensing respiratory movement whereby the light source shines through the modulation reed onto the sensor.
FIG. 3 is an alternate indirect modulation method whereby light is reflected from a surface behind the reed onto the sensor.
FIG. 4 is a perspective view of a portion of the belt.
FIG. 5 is a top plan view of the belt shown in FIG. 4 with the transducer and modulation reed mounted thereon.
FIG. 6 is a perspective view of a detail of the adhesive disposable used as an alternative means of mounting the transducer and reed.
FIG. 7 is a top plan view of the transducer and reed attached with the adhesive disposable pads.
FIG. 8 is a side elevation view of the transducer and light sensing housing with the belt shown in dotted lines.
FIG. 9 is a cross-sectional view of another modulation reed.
FIG. 10 is a schematic circuit diagram of the sensing electronics system.
FIG. 11 is a diagrammatic view of the sensing unit mounted longitudinally on the upper abdomen and chest.
FIG. 12 is a diagrammatic view with the sensing unit mounted transversely on the abdomen.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
The motion sensing unit is mounted on the back, front or side of the patient as shown in FIGS. 11 and 12 and is comprised of the modulation reed 46 and grid 60 and the transducer 14. The internal details of the transducer are shown in FIGS. 2 and 3. The transducer housing 16 to which is attached an electrical wire 18 leading to the transducer is shown in FIG. 8. The housing 16 contains the light sensor 20 which converts light energy to electrical energy, which is well known in the art, and is activated by means of a small focused light source 22, which is also mounted in the housing 16. The relative motion of two points on the skin surface is monitored by a unique light modulation technique. The relative motion of the grid 60 on the modulation reed 46 in the transducer slot 28 causes the light intensity impinging on the sensor to change thus changing the sensors resistance (resistor) or turning it on and off (transistor). This can be accomplished either by a direct modulation technique whereby the light is shined through the reed onto the sensor (FIG. 2) or by an indirect modulation technique whereby light is reflected from a surface behind the reed (FIG. 3). The sensitivity of the transducer can be adjusted by changing the width of the modulation bars (grid) on the reed and the width of the sensor aperature and by changing the intensity and type of light source and the type of sensor.
As shown in FIGS. 4 and 5, the mounting belt 30 comprises a pair of pockets 40 in which are mounted the transducer 14 and modulation reed 46. The transducer is mounted by means of a tongue formed by the bottom portion 26 of the housing 16, and the reed is mounted by means of a slotted tongue 44 on the reed arrangement 46. The reed 46 includes an elongated connection member 48 which contains the modulation medium or grid 60. The motion sensing unit can also be mounted by adhesive mounting pads 52 which have pockets 40' for mounting the transducer or reed.
The grid 60 of the modulation reed can either be perforated to allow the passage of light, or be a clear plastic with an opaque set of bars or circular discs. The reed material must be thin and flexible to allow it to conform to the curvature of the body between the transducer and the reed mounting point without causing excess friction in the slot 28 on the transducer.
The transducer housing 16 and the reed 46 are attached to the patient by the belt 30 but they also may be attached by means of disposable adhesive (FIG. 6) or any other suitable method which allows the reed 46 to move relative to the slot in the transducer as respiration occurs. The transducer housing 16 and reed 46 are preferably placed in the position where the relative motion between the two attachment points is at least 0.5 mm so that the transducer will translate the signal. If the transducer housing 16 and reed 46 are attached with the disposable adhesive, there are many positions and alignments of the body which will provide for satisfactory monitoring even on the smallest premature infant with very shallow breathing pattern. Some infants have most respiratory motion occurring between the upper abdomen 54 and the lower rib cage 56. In this case, the transducer housing 16 and reed 46 can best be mounted so that the reed 46 is aligned with the length of the body (See FIG. 11). The transducer housing 16 is mounted on the upper abdomen 54 above the navel 58 and the reed is attached to the chest 56 above the transducer. Other infants have more motion occurring from the expansion of the diameter of the abdomen 54 and in this case the transducer housing 16 and reed 46 should be mounted from left to right and perpendicular to the actions of the body on the upper abdomen 54 as shown in FIG. 12. If the rubber belt 30 is used, it can be placed around the abdomen 54 either above or below the navel 58. The transducer housing 16 and reed 46 can be placed either on the abdomen or back of the patient.
The alignment of the reed 46 and the transducer housing 16 is not so critical due to the shape of the reed slot 44 shown in FIG. 9. The "hourglass" shape allows misalignments of up to 30° before the reed 46 binds in the slot. The reed 46 is only wide enough to cover the sensor aperture while in contact with one wall of the aperture. The sensor aperture 24 is square to increase sensitivity.
DESCRIPTION OF THE ELECTRONIC CIRCUIT FIG. 10 (Example)
Basically the circuit disclosed in FIG. 10 detects modulated light from the transducer to the circuit and includes resistors R1 through R 17; transistors Q1 thru Q7; capacitors C1 and C2; switch S1. When light modulation ceases for a period of 6 to 30 seconds (adjustment is made by changing the value of R11) an alarm B is sounded. Changes in light intensity are detected by the photoresistor PR as shown or by any other suitable device such as a photo-transistor or photo-darlington. These light changes result in a voltage change across resistor R2. The FET (abbreviation for unipoler field effect transistor) Q1 provides the needed impedance conversion between R2 and the input Q2. However, the signal from R2 is not amplified by Q1. The capacitor C1 isolates the D.C. voltage bias to the input of Q2. R5 serves as a sensitivity adjustment. The transistors Q2 and Q3 operate as a unit to provide high amplification. In fact, in this application transistors Q2 and Q3 saturate at approximately 4.5 volts in the presence of the input signal across R5. Therefore, the voltage from the input side of R10 to ground is either 0 volts in the absence of light modulation or 4.5 volts when light is being modulated. Q4 operates as a switch, which is on when the voltage across R10 is high. When Q4 is turned on, a charging current is supplied to the capacitor C2. The voltage across C2 increases turning on transistor Q6, this lowers the voltage at the input of R15 and turns off Q7. In this state the audio alarm B is silent. However, when light modulation stops, the voltage across C2 decreases slowly providing a time delay controlled by R11. When C2 is discharged the voltage at the input of Q7 is high and Q7 conducts thereby turning on the audio alarm B.
The indicator light L provides a visual indication as to the state of the system. This light L is controlled by a darlington transistor pair Q5. When switch S1 is placed in the test position the indicator light L burns intermittently or constantly depending on the respiration rate when the transducer T is being modulated, i.e., a normal condition exists. However, when the switch S1 is switched in the ON, the light L is turned off and only burns when the audio alarm is sounding, i.e., respiration ceases.
The L.E.D. (light emitting diode) CRI is located remotely in the transducer T, and provides the light source for the photo-resistor PR which is also remotely located in the transducer T.
This device is inherently fail-safe to the discharge of the battery. As the supply voltage decreases, the system sensitivity decreases. When the sensitivity has decreased sufficiently the system will react, as if a patient respiration failure had occurred and the audio alarm B will be sounded. Low battery voltage may then be verified by observing the battery level indicator also.
SUMMARY OF OPERATION OF DEVICE
The rhythmic breathing of the patient causes the static or passive condition of the system, that is, as long as the light from the light emitting diode L.E.D. is broken regularly and rhymically by the "shutter" 32 of the reed 46, the voltage changes occur across the photo-resistor and these changes are amplified and utlilized to keep the alarm clock deactivated. When breathing stops for a period of time (e.g. 6 to 30 seconds) the change in the intensity light impinging on PR ceases and the Alarm B is sounded after the preset time delay.
While I have shown and described a preferred embodiment of my invention with suggested modifications, this is by way of illustration only and does not constitute any sort of restriction thereon, since there are various alterations, changes, deviations, departures, omissions, additions, and variations which may be made in the disclosed invention without departing therefrom as determined only by reference to a proper construction of the appended claims.