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Publication numberUS3760794 A
Publication typeGrant
Publication dateSep 25, 1973
Filing dateSep 1, 1971
Priority dateSep 1, 1971
Publication numberUS 3760794 A, US 3760794A, US-A-3760794, US3760794 A, US3760794A
InventorsR Basham
Original AssigneeElectronic Monitors Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Respiration monitoring apparatus and method
US 3760794 A
Abstract
Apparatus and method for monitoring the respiration of a patient through utilization of a force responsive transducer, which ideally is a capacitor transducer constructed from alternate layers of conductive and nonconductive materials that are flexible such that when placed beneath a patient or a resilient patient support, such as a mattress, the distance between the plates of the transducer changes for the purpose of producing electrical responses that upon amplification energize indicator means, such as a visual alarm or an audible alarm. The transducer is responsive to the vertical, reciprocating forces and motions caused by respiration and along with the associated circuitry, is sufficiently sensitive to energize an alarm upon sensing a cessation of respiration.
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Description  (OCR text may contain errors)

' United States Patent [191 Basham RESPIRATION MONITORING APPARATUS AND METHOD [75] Inventor; Raymond B. Basham, Fort Worth,

' Tex.

[73] Assignee: Electronic Monitors, Inc., Fort Worth, Tex.

[22] Filed: Sept. 1, 1971 [21] Appl. No.: 176,983

Related US. Application Data [63] Continuation-impart of Ser. No. 97,737, Dec. 14,

1970, abandoned.

[52] U.$. Cl 128/2 R, 128/25, 317/261,

340/279 [51] Int. Cl. A6lb 5/08 [58] Field of Search 128/25 R, 25 N, 2.08,

128/2.1 R, DIG. 17, 2.05 P; 73/398 C, 88.5 R; 340/279; 317/261 [111 3,760,794 Sept. 25, 1973 Primary Examiner -Kyle L. Howell Attorney-William T. Wofford et a1.

[5 7] ABSTRACT Apparatus and method for monitoring the respiration of a patient through utilization of a force responsive transducer, which ideally is a capacitor transducer constructed from alternate layers of conductive and nonconductive materials that are flexible such that when placed beneath a patient or a resilient patient support, such as a mattress, the distance between the plates of the transducer changes for the purpose of producing electrical responses that upon amplification energize indicator means, such as a visual alarm or an audible alarm. The transducer is responsive to the vertical, reciprocating forces and motions caused by respiration and along with the associated circuitry, is sufficiently sensitive to energize an alarm upon sensing a cessation of respiration.

11 Claims, 9 Drawing Figures SkEEI U 0F 4 mimmmsw SOUND A LIgRM 3 0 V DC 30V DC BACKGROUND OF THE INVENTIO 1. Field of the Invention This invention relates in general to patientmonitoring apparatus, particularly to apparatus adapted to monitor respiration for the purpose of providing an alarm upon cessation of respiration.

2. Description of the Prior Art A number of different types of methods and apparatus have been proposed in the past for the purpose of monitoring'respiration. However, the previously known apparatus and methods have not'yet received widespread acceptance due to a number of severely limiting disadvantages. One previously known method utilizes the connection of electrodes directly to the skin of a patient to sense electrical resistance changesduring respiration in the skin surrounding the expanding and retracting chest cavity. Connecting electrodes directly to the patient is often irritating to the patient, whose skin frequently rejects the saline solution commonly used to produce satisfactory contact between the electrode and the patient. And in addition, such method can be dangerous if a large voltage is applied inadvertently or accidentally across electrodes secured to a patient. A number of accidents of this type have been reported. In addition, devices have been proposed for sensing force of motion cessation that include the use of a photoelectric cell, but such devices lack that degree of sensitivity leading to successful operation.

SUMMARY OF THE INVENTION It is the general object of the invention to provide improved respiration monitoring apparatus and methods that accurately sense respiration and cessation of respiration without need for direct attachment to the body.

Another object of the invention is to provide respiration monitoring apparatus that utilizes a capacitor transducer for accurately sensing respiration and cessation of respiration;

Another object of the invention is to provide an apparatus and method for respiration monitoring that utilizes electrical responses from a capacitor transducer, that amplifies such responses, and that transmits the responses to either an audible or visual indicator and circuit means to notify a patients attendant that respiration has ceased.

The invention comprises respiration monitoring apparatus and method, the apparatus including a force responsive transducer, which ideally is a capacitor transducer with movable plates, adapted for placement beneath a patient or a patient support such as a mattress. The transducer senses changes in the forces and movements caused by patient respiration. By suitably amplifying the electrical responses generated with the transducer, these responses may be fed to indicator means that provide either a visual or an audible warning that signifies when the electrical responses cease due to cessation of respiration. The indicator means are ideally a lamp, for visual warning and an audible device such as a speaker, for audible warning, to signify the cessation of electrical response. Such apparatus and method are sufficiently sensitive and accurate to sense cessation in the generally vertical, reciprocating forces generated by patient breathing. I-Ience, should this bodily function cease, the visual and audible alarms are energized.

In one embodiment a memory device is provided that continuously indicates that temporary cessation had occurred in the event that the patient recovers and begins breathing again.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of respiration monitoring apparatus positioned relative to a patient lying in a conventional hospital bed in accordance with the principles of my invention.

FIG. 2 is a perspective view of a force responsive transducer, with portions thereof separated to show the construction thereof.

FIG. 3 is an electrical schematic diagram showing a preferred circuit for energizing both a visual and an audible alarm to indicate cessation of respiration.

FIG. 4 is an electrical schematic diagram of an amplifier circuit shown in block form in FIG. 3.

FIG. 5 is an electrical schematic diagram of a lamp switching circuit shown in block form in FIG. 3.

FIG. 6 is an electrical schematic diagram of an audio switching circuit shown in block form in FIG. 3.

FIG. 7 illustrates in more detail the manner in which electrical connections are made to the transducer.

FIG. 8 is an electrical schematic diagram of an alternative warning system incorporating a memory device.

FIG. 9 is an electrical schematic diagram of a rate meter for indicating the rate of respiration of a patient.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring initially to FIG. I of the drawing, the numeral ll designates a force responsive transducer inserted between the mattress I3 and springs (not shown), generally under the shoulder region of a patient 15 in a reposed position in a conventional hospital bed I7. The force responsive transducer 11 is connected by a coaxial cable 19 with a console 21, which is in turn connected by multi-line conductor 23 and plug 24 with a wall socket 25 associated with a l 10 volt alternating current source. As shown in FIG. I the console 21 has exposed on its exterior an audible alarm 27 and two visual alarms 29, 31, the operation and function of which will be explained subsequently.

Referring to FIG. 2, the force responsive transducer 11 is preferably a capacitor transducer comprised of layers of flexible, alternately conductive and nonconductive material as follows. The exterior of the capacitor 33 is of a nonconductive material such as an acrylic or cellulose, the lower side of such covering material having a flap 35 adapted to fold over and bond to the upper cover. As shown in FIG. 2 the next material from the top is preferably a flexible conductive sheet 37 of suitable material such as sheet steel that is adjacent a nonconductive sheet of material 39 that in turn lies adjacent a conductive sheet 41 on top of a nonmetallic sheet 43 adjacent an exterior conductive sheet 45 that is covered by material 33, as previously explained. The sheets 39, 41 and 43 are secured in this instance with a nonconductive strip 46. The outer conductive sheets 37 and 45 not only provide the reference plates to establish capacitance with respect to the inner plate 41 but also shield the inner plate from stray electric fields.

The coaxial cable 19 leading from the transducer to the console 21 has its center conductor 19A connected to the conductive sheet 41 as illustrated in FIG. 7. The shield 19B of cable 19 is connected to the two outer conductive sheets 37 and 45 as illus'trated'by connection 19B. At the console the shield 19B is grounded as illustrated at 47. An example of a satisfactory conductive material issheet steel metal of about0.003 inch thickness, While a satisfactory nonconductive material I is acrylic havinga thickness of approximately 0.003 of an inch. The alternate layers of conductive-and nonconductive material may be approximately 6 inches square. Hence, thecomposite transducer has the characteristics of flexibility and pliability for the purpose of accurately sensing force changes upon the mattress 13.

Referring initially to FIG. 3, which is a schematic diagram of a preferred circuit means, the numeral 11 designates the variable capacitor transducer illustrated in .FIGS.'2 and 7. The cable conductor 19A is connected with the juncture 49 of a resistor 50 and a protective network 53 that comprises in this instance a biasing resistor 55 connected in parallel with diodes 57, 59, which are in turn connected with the juncture 61 of two source resistors 63 and 65, 65 being connected with I ground 47 as shown.

.two lamps 29, 31 (see also FIG. 1) or othersuitable visual indicators, and second an audio switching circuit 85 that drives a speaker 27 (see also FIG; '1).

Describing the FIG. 3 circuit operationally; the field effector transistor 69 is connected in a source follower configuration with the resistors 63 and 65, which are connected with the source, in this instance the variable capacitor 11. The resisotr 63 supplies the bias to regulate the gate c'ut-ofi' point on the field effect transistor. The voltage developed across resistor 65 is supplied back to the capacitor 1 1 through resistor 55, and polarizes the capacitor transducer in such a way that it will act upon this voltage but will produce a variable voltage that is inversely proportional to the change in the capacitance of the transducer. This variable voltage is then sensed through resistor 50 by the gate 67 of the field effect source follower. The output of the field effect source follower is transmitted to the juncture .61 of resistors 63, 65, which are connected through capacitor 75 to the amplifier. In operation each time pressure is applied to the capacitor transducer 11, a signal appears at the output of the amplifier circuit 77. The resulting amplified signalis applied to the lamp switching circuit 79. The respiration lamp 29 responds to cyclic breathing pressure applied through the mattress 13 to the transducer. This lamp is adapted to flash each time there is breathing motion applied to the capacitance transducer by the mattress. So-long as the cyclic mattress motion caused by patient breathing continues, the respiration lamp 29 will continue to light cyclically.

In the event of respiration failure of the patient, the respiration lamp will extinguish and after a period of time determined by the setting of adjustable resistor 225, the alarm lamp 31 will switch on. This in turn applies an AC signal into the audio swtiching circuit 85, which in turn closes the switching circuit in order to excite an audible alert device that can be a buzzer, but preferably is a solid state transistor signalling device that gives an audible alarm simultaneous with the emergency lamp.

Referring to FIG. 4 for an explanation of a preferred amplifier circuit, the drain 71 of the field effect transistor 69 is connected at the juncture 87 of a resistor 89 which is connected in series with the collector 91 of a transistor 93. The base of the transistor 93 is connected with the juncture 94 between the output of capacitor 75 and a resistor 97, the collector 91 being connected with the juncture 99 between resistors 89 and 97. The emitter 98 of transistor 93 is connected to ground. The juncture 99 is connected with a capacitor 101 connected in series with a resistance 103, which in turn is connected at the juncture 105 of a resistor 107 and the base 109 of a transistor 111.

The juncture 105 and the base 109 of transistor 111 is connected with a diode 113 through a juncture 115 leading to a capacitor 1 17. A resistor 119 is connected with ground and with the juncture 121 between capacitor l 17 and a capacitor 123, which is in turn connected with the juncture 125 between resistance 127 and the collector 129 of transistor 111, such juncture also connecting resistors 107 and 127 as shown. Resistor 127 is connected at a terminal 139 and thus across an unregulated 35 volts (DC). The conductor 132 and terminal 134 define the output of the amplifier circuit.

The 35 volt source-is derived typically from a plug 24 of a 110 volt AC source that is connected across the primary 133A of a transformer 133, the secondary 135 that in turn is connected through a rectifier, which in this instance is a diode 137 connected between the juncture 139 between resistor 127 and capacitor 141 connected to ground as shown.

A regulator circuit comprises a transistor 143 having its emitter 145 connected at a juncture 147 between resistor 149 and a conductor 151 leading to the juncture 87 between resistor 89 and the field effect transistor 69. The collector 153 of transisotr 143 is connected with the 35 volt unregulated supply via conductor 155, and its base 157 is connected with the juncture 159 of a resistor 161 and the collector 163 of a transistor 165. The opposite terminal 167 of resistor 161 is connected with the conductor and thus the 35 volt unregulated source. The base 169 of transistor is connected to the juncture 171 between resistors 149 and 173. The emitter 175 of transistor 165 is connected with the cathode of a Zener diode 177, the anode of such diode being connected to ground and to resistor 173 as shown. In addition, the cathode of the Zener diode 177 is connected with the juncture 179 between a resistor 181 and the emitter 175 of transistor 165. The resistor 181 is connected at terminal 183 with the conductor 155 leading to the 35 volt source.

The regulator circuit shown is of conventional form, using a 15 volt Zener diode as a reference and a voltage divider device transistor 165 which in turn controls the base of the transistor 143, the output of the regulator then being the reference voltage difference in the voltage divider defined by resistors 149 and 173 for setting the bias operation point for transistor 165, which would "be the 25 volt "point plus'the forward voltage drop across transistor 165.

Operationally, the above described amplifier circuit consists of two stages, that include respectively transistor 93 and transistor 1 11, having their capacitance coupled. Transistor 1 1 1 has a low pass filter of the negative feed-back type connected between the collector and the base of transistor ,1 1 1. This filter consists of capacitors 117, 123 and resistor 119. This network provides a necessary'frequency feed-back in order to give the amplifier relatively low frequency roll off so that any signals above and higher than the frequency of normal respiration signals are rejected, and the gain of the amplifier is thus extreme for such signals.

A preferred lamp switching circuit is illustrated in FIG. 5 with the output 134 of the amplifier circuit being connected in series witha resistor 185 and a capacitor 187', which is connected at the juncture 189 between a conductor 191 and aresistor 193 leading to ground 47. Conductor 191 leads to the juncture 195 between a resistor 197 and a diode 199, also "connected with ground. The output of resistor 197 is connected withthe gate 200 of a'silicon controlled rectifier 201 having its anode 203 connected in series with the lamp 29, which is connected with the 30 volt source 204 as shown, the cathode 205 of the rectifier being connected with ground.

The anode 203 of rectifier 201 is connected through a juncture 209 with a resistor 207, in turn connected through a juncture 211 between a capacitor 213 that is grounded as shown. The diode 215 is connected in series. with a resistor 217, which is connected with the juncture 219 between a capacitor 221, connected with ground, and a resistor 223 connected in series with a variable resistor 225 connected to the 30 volt AC source applied to the conductor 227.,

The gate 228 of a silicon controlled rectifier 229 is connected with the juncture 219 between capacitor 221 and resistors 217, 223, while the cathode 231 is connected to ground and the anode 233'is connected with the lamp 31 and with a lamp 29 through conductor 227. An output conductor 235 leads from the juncture 237 between lamp 31 and the anode 233 of the rectifier 229., r I Y Operationally, the respiration lamp switching circuit 7.9-comprises'the silicon controlled rectifier 201 that switches the lamp 29 on each time there is a respiration signal from the transducer 11. The anode 203 of the rectifier 201 is connected to the capacitor 213 in order to maintain a charge on this capacitor so that the emergency lamp 31 will remain off during the time that the charge ismaintained. Each time rectifier 201 is energized and the respiration lamp 29 is turned on there is a negative voltage appearing at the anode 203 of the rectifier 201, and this in turn maintains a negative I charge on capacitor 213.

With respect to rectifier 229, the emergency lamp switching rectifier, would normally keeo the emergency light 31 energized if it were not for the negative charge maintained on the capacitor 213. Failure of patient respiration or a failure of the respiration lamp 29 would no longer maintain a negative charge on capacitor 213, and thus, the emergency lamp 31would be ex-.

cited. As a consequence, that in the event of failure of the respiration light 29, the instrument will give alarm. Such a malfunction energizes theenergency lamp 31 and the audible alarm (as explained subsequently) so that the patient attendant whould know-that there was either an emergency or there had been a failure of the instrument. Any failure in the circuitry described thusfar will energize lamp 31; this in turn tends to make the whole instrument essenatially fail safe.

A preferred audio switching circuit is illustrated in FIG. 6, in which a resistor 239 is connected with the output 235 of the lamp switching circuit and with a juncture 241 between resistor 239 and a capacitor 245 connected to ground. The resistor 243 is connected with the juncture 244 between a resistor 247 and the base 249 of a transistor 251, having its collector 253 connected with the juncture 255 between a resistor 257 and a resistor 259, and its emitter 261 connected to ground as-shown. Resistor 247 and resistor 257 are connected with a juncture 263 leading to the 35 volt DC source Resistor 259 is connected with the juncture 265 between a base 267 of a transistor 269 and a resistor 271 conditions a positive bias is supplied to the base of transistor 269, which switches on the transistor and in turn causes current to flow through an audible alert device such as speaker 27. When the emergency lamp 31 is in the off condition, there is no charge applied to the capacitor 245, such that transistor 251 is biased in the forward direction through resistor 247. This in turn drops the base current to zero in transistor 269, which in turn cuts off this transistor to prevent current flow to the audio alert device.

In hospitals, where a plurality of the devices of the present invention may be employed simultaneously to monitor the breathing'of a plurality of newborn babies respectively, means is needed to allow an attendant nurse to know if a given baby has experienced temporary cessation of breathing but has subsequently recovered. For example, while the nurse is attending to one baby, a baby behind her may experience temporary cessation of breathing causing the lamp 31 of its associated monitor to be energized and its alarm 27 to sound. By the time the nurse turns around, breathing may be restored causing the monitor lamp 31 to turn off and the alarm 27 to terminate its sounding. Thus the nurse will not be able to know which baby had temporary problems from observing the monitors employed.

Referring to FIG. 8, there will be described a circuit arrangement incorporating a memory device which will retain evidence of cessation of breathing if it occurs by the baby being monitored by a given monitor. This circuitry is a modification of that of FIG. 5 with additional components employed. In this respect, transistor 281 is substituted for silicon controlled rectifier 229 and the lamp 31 removed from the position shown in FIG. 5. The lamp is connected as shown at 31' in FIG. 8 to a silicon controlled rectifier 283 which is employed for memory purposes. The remainder of the circuitry of F IG. 8 comprises a transistor 285, a unijunction transistot 287, a transistor 289 and a capacitor 297. Transistor 287 and capacitor 297 forman oscillator. Normally when a patient is breathing, transistor 281 is in a nonconductive state, transistor 285 is conducting, unijunction transistor 287 is off or in a nonconducting state, silicon" controlled rectifier 283 is off or in a nonconducting state and transistor 289'is conducting. Thus lamp 31 is off and the sound or audible alarm 27 coupled between the silicon controlled rectifier 283 and transistor 289 also is off. When transistor 281 is off, a positive bias is applied to the base of transistor 285 maintaining it in a conductive state. The resulting low potential from the collector of transistor 285 maintains the transistor 287 in a nonconducting state, The transistor 289 is biased to a conducting state through resistor 295.

. When a patient stops breathing, transistor 281 becomes conductive thereby causing transistor 285 to become nonconductive. This causes the oscillator to begin oscillating for the production of positive pulses which are applied to the gate of silicon controlled rectifier 283 and negative pules which are applied to the base of transistor 289. The first positive pulse applied to the gate of silicon controlled rectifier 283 renders it in a continuous conductive state while each negative pulse applied to the base of transistor 289 renders it temporarily nonconducting. Thus since silicon controlled rectifier 283 is on and transistor 289 is turned on and off, lamp 31' periodically is energized to flash on and off. As the lamp 31' flashes on and off a negative pulse periodically is applied to the sound alarm 27 by way of capacitor 291 to periodically turn the sound ,alarm on and off also. If the patient begins to breath sured. The Zener diode 319 is provided in order to regcontrolled rectifier 283 to their normal conditions, the I attendant merely has to temporarily close switch 293 to ground the anode circuit of the silicon controlled rectifier 283 inorder to place the rectifier in its normal nonconducting state.

Referring to FIG. 9, there is disclosed circuitry and a device which may be employed as a visual indicator of breathing in addition to the lamp 29. This circuitry comprises a rate meter and may be coupled to the amplifier of FIG. 4 at terminal 134. In the circuitry of FIG. 9, transistor 301 normally is off but is turned on each time respiration occurs. Transistor 303 normally is on when there is no respiration but becomes nonconductive when transistor'30l becomes conducting. A capacitor 305 is charged through transistor 303 when it is ulate the voltage that is supplied to the capacitor 305 in order that the voltage supplied to it is a very accurate reference voltage.

From the above apparatus and operational descriptions, it should be apparent taht l have provided an invention having significant advantages. By placing the force responsive transducer beneath the patient as shown in FIG. 1, the respiration of the patient may be sensitively monitored. The transducer is sensitive to the generally vertical, reciprocating motions transmitted to the mattress 13 by the patients respiration. As a consequence, should the patients respiration be interrupted, the visual and audible alarms associated with the console will be energized for the purpose of alerting the patients attendant. For the first time an apparatus has been provided that possesses sufficient sensitivity to monitor accurately respiration without requiring direct attachment to the patient.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes and modifications without departing from the spirit thereof. The specific form of force responsive transducer is not limited specifically to the capacitor transducer shown and described, and the configuration of the capacitor transducer itself may be varied widely within the broad scope of the invention. In addition, the invention is not limited in its broadest sense to the specific form of circuitry shown by way of preferred embodiment, since there are alternate circuit configurations capable of producing the intended, satisfactory result.

I claim:

1. A system for monitoring the respiration of a patient comprising:

a flexible force responsive capacitor means for placement beneath a patient or patient support for sensing the respiration of a patient, said capacitor comprising:

three layers of flexible sheets of electrically conductive material,

a flexible sheet of electrically non-conductive material located between adjacent sheets of conductive material to form alternate layers of conductive and non-conductive sheets of material,

the outer conductive sheets being larger than the center sheet and having their peripherical edges substantially contiguous to each other so as to provide effective electrostatic shielding for the center conductive sheet,

said flexible layers of conductive material being sensitive to changes in forces applied thereto and caused by the respiration of a patient,

an electrical conductor connected to the center sheet of conductive material,

an electrical conductor connected to the outer sheets of conductive material, and

flexible non-conductive material surrounding and covering said outer layers of flexible sheets of conductive material,

means connected to said conductors for applying a substantially constant voltage across said capacitor, and

monitor means coupled to said capacitor means for monitoring the respiration of a patient.

2. A system for monitoring the respiration of a patient comprising:

a capacitor transducer means capable of sensing force changes applied thereto and caused by the respiration of a patient,

said transducer being a thin, flexible, pad-like member, comprising:

a plurality of thin flexible layers of electrically conductive material including two outer layers,

a thin flexible layer electrically nonconductive material located between adjacent layers of conductive material to form alternate layers of conductive and nonconductive material, I

two electrical conductors connected to certain ones of said conductive layers to form a capacitor having two plate means, one of which includes the outer conductive layers of material electrically connected together,

the other plate means being located between said outer conductive layers of material,

the outer layers of said conductive material having their peripherical edges extending beyond said other plate means and substantially contiguous to each other so as to provide effective electrostatic shielding for said other plate means and flexible electrically nonconducting material surrounding and covering said outer conductive layers said flexible layers of conductive material being sensitive to changes in forces applied thereto and caused by the respiration of a patient,

means connected to said conductors for applying a substantially constant voltage across said capacitor transducer, and

monitor means coupled to said capacitor transducer means for monitoring the respiration of a patient.

3. The system of claim 2 wherein said means for applying a substantially constant voltage across said capacitor supplies a substantially constant voltage of less than 25 volts DC.

4. The system of claim 2 wherein said plurality of layers of electrically conductive material comprise an odd number of layers.

5. The system of claim 2 including the combination therwith of a memory system comprising:

a lamp indicator means,

circuitry means coupled to said capacitor transducer for periodically energinzing said lamp indicator means to cause said lamp indicator means to flash on and off when respiration ceases,

said circuitry including means for continuously energizing said lamp indicator meansif respiration begins following cessation thereof.

6. The apparatus of claim 5 wherein said circuitry comprises:

normally electrically nonconducting means coupled to said lamp indicator means and which is rendered electrically conductive by the application of a signal thereto and which remains in a conductive state following termination of said signal,

a normally conducting means coupled to said normally nonconducting means for providing a flow path of energy from said normally nonconducting means, and

ill

oscillator means coupled to said normally nonconducting means and to said normally conducting means and responsive-to cessation of respiration for producing periodic signals for rendering con- 5 ductive said normally nonconducting means and for periodically rendering said normally conducting means nonconductive to periodically cuase said lamp indicator means to flash on and off. 7. A system for monitoring the respiration of a person comprising: 7

a capacitor transducer means capable of sensing force changes imparted to a mattress or the like due to the respiration of a person while supported by the mattress, said transducer being a thin, flexible, pad-like member comprising: alternate layers of thin flexible sheets of electrically conductive and nonconductive material forming a thin and flexible capacitor having a ratio of surface area in the plane of said pad-like member relative to its thickness through said sheets of greater than 500 to one,

the number of layers of conductive material being greater than two,

two electrical conductors connected to certain ones of said conductive sheets of material to form a capacitor having two plate means, one of which includes the outer conductive sheets of material electrically connected together,

the other plate means being located between said outer conductive sheets of material,

the outer layers of said conductive sheets of amterial have their peripherical edges extending beyond said other plate means and substantially contiguous to each other so as to provide effective electrostatic shielding for said other plate means, and

thin flexible electrically nonconductive material surrounding and covering said outer layers of electrically conductive sheets of material,

said flexible sheets of conductive material being sensitive to changes in forces applied thereto and caused by the respiration of a patient,

means connected to said conductors for applying a substantially constant voltage across said capacitor transducer, and

monitor means coupled to said capacitor transducer means for monitoring the respiration of a patient.

8. The system of claim 7 wherein the number of layers of conductive material comprise an odd number of layers.

9. A system for monitoring the respiration of a patient comprising the combination of:

a capacitor transducer means capable of sensing force changes applied thereto and caused by the respiration of a patient,

said capacitor transducer comprising a thin, flexible pad-like member including alternate layers of thin flexible sheets of electrically conductive and nonconductive material forming a thin and flexible capacitor having a number of layers of conductive material greater than two,

two electrical conductor means connected to certain ones of said conductive sheets of material to form a capacitor having two plate means, one of which includes the outer sheets of conductive material regulator means for producing a regulated supply of voltage from said supply of electrical energy, and

' a field effect transistor'connected in a source follower configuration and having its drain connected to the output of said regulator means; its gate connected to the otherof said conductor means and hence to said other plate means 'of said capacitor transducer; its source connected,

to said one conductor means by way of a source biasing resistor and a load resistor; and a gate return resistor having one terminal connected to said gate and the other terminal connected to the juncture between said source biasing resistor and said load resistor and monitor means coupled to the source of said field effect transitor for monitoring the respiration of a patient.

10. The system of claim 9 wherein said capacitor transducer means includes three conductive layers of material, the outer layers of conductive material being larger than the center layer and having their peripherical edges substantially contiguous to each other to provide effective electrostatic shielding for the center layer.

1 l. A method of monitoring the respiration of a person supported on a mattress or the like comprising the steps of:

locating a capacitor transducer at a position sufficient to sense force changes imparted to the mattress caused by the respiration of the person while supported by the mattress,

said capacitor transducer comprising:

three layers of flexible sheets of conductive material,

a flexible layer of non-conductive material located on opposite sides of the center sheet of conductive material, the flexible layers of non-conductive material on opposite sides of said center sheet of conductive material having their edges connected together forming an inner member having a covering of non-conductive material surrounding said center sheet of conductive material, an exterior flexible non-conductive layer of material covering the outward facing side of each of the outer sheets of conductive material, the exterior flexible non-conductive layers of material having their edges connected together forming an exterior covering of non-conductive material surrounding said outer sheets of conductive material with said inner member located between said outer sheets of conductive material, said outer sheets of conductive material being larger in their planes than said center sheet of conductive material and having their peripherical edges extending beyond the peripherical edges of said center sheet of conductive material so as to provide efi'ective electrostatic shielding for said center sheet of conductive material, said flexible layers of conductive material being sensitive to changes in forces applied thereto and caused by the respiration of a patient, an electrical conductor connected to said center sheet of conductive material, and an electrical conductor connected to said outer sheets of conductive material, applying a substantially constant voltage to said two conductors and hence across said capacitor transducer, sensing capacitive changes between said layers of flexible sheets of conductive material due to force changes applied thereto due to the respiration of said person, converting said sensed capacitive changes into electrical responses, amplifying said electrical responses, and applying said electrical responses to a monitor means.

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Classifications
U.S. Classification600/535, 340/665, 340/657, 340/573.1, 361/283.1, 601/41
International ClassificationA61G7/043, A61B5/113
Cooperative ClassificationA61B5/6892, A61B5/113
European ClassificationA61B5/68F4, A61B5/113