Pulmonary resuscitator with electrical control system

Aug. 1, 1967 E. W. ROBINSON ET AL 3,333,581

PULMONARY RESUSCITATOR WITH ELECTRICAL CONTROL SYSTEM

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PULMONARY RESUSCITATOR WITH ELECTRICAL CONTROL SYSTEM

Filed March 27, 1964 4 Sheets-Sheet 3

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PULMONARY RESUSCITATOR WITH ELECTRICAL CONTROL SYSTEM

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Aug. 1, 1967

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BY ^&amp; Attorn^s

United States Patent Office

3,333,581

Patented Aug. 1, 1967

333 581

PULMONARY RESUSCITATOR WITH ELECTRICAL CONTROL SYSTEM

Elbert W. Robinson, 2601 Harmony 79106; 'James A. Miller, 2211 Crockett 79109; and Loyde H. Hudson, 4222 W. 2nd 79106, all of Amarillo, Tex.

Filed Mar. 27, 1964, Ser. No. 355,177

Claims. (CI. 128—30.2)

This invention relates to apparatus for resuscitating a patient by either assisting breathing or inducing breathing artificially.

A primary object of the present invention is to provide apparatus capable of being regulated in accordance with different requirements and situations for the resuscitation of patients exhibiting breathing difficulties.

An additional object of the present invention in accordance with the foregoing object, is to provide a control system for a resuscitator whereby its operational mode may be regulated and changed in accordance with different needs.

A still further object of the present invention is to provide a resuscitator having facilities for sensing the breathing action of a patient so that the resuscitator may be regulated in accordance with the patient’s demand to assist breathing.

Another object of the present invention is to provide a resuscitator control system which may automatically induce breathing of a patient at a preselected rate and respond to any attempt on the part of the patient to resume natural breathing by converting operation of the resuscitator to regulation by patient demand.

Yet another object of the present invention is to provide a novel low pressure sensing device for rendering the resuscitator operative to regulate breathing in accordance with the natural breathing rate of the patient.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIGURE 1 is a perspective view of the apparatus of the present invention being used.

FIGURE 2 is a sectional view taken substantially through a plane indicated by section line 2—2 in FIGURE 1.

FIGURE 3 is a sectional view taken substantially through a plane indicated by section line 3—3 in FIGURE 1.

FIGURE 4 is a sectional view taken substantially through a plane indicated by section line 4—4 in FIGURE 3.

FIGURE 5 is a sectional view through the sensor device.

FIGURE 6 is a sectional view taken substantially a plane indicated by section line 6—6 in FIGURE 5.

FIGURE 7 is a partial sectional view taken substantially through a plane indicated by section line 7—7 in FIGURE 5.

FIGURE 8 is an enlarged partial sectional view taken substantially through a plane indicated by section line 8—8 in FIGURE 6.

FIGURE 9 is a top plan view of the control panel associated with the resuscitator apparatus.

FIGURE 10 is a schematic control circuit diagram corresponding to the apparatus of the present invention.

FIGURE 11 is a work flow diagram diagrammatically illustrating the control system associated with the present invention.

FIGURES 12A and 12B are electrical circuit diagrams illustrating one form of control system associated with the present invention.

Referring now to the drawings in detail, and initially 5 to FIGURE 1, it will be observed that the resuscitator apparatus generally referred to by reference numeral 10 when in use may assist or induce breathing of a patient 12 by alternatively applying pressure and vacuum through a flexible outlet conduit 14 to a chest shell device 16 placed 10 about the patient so as to expand and collapse the patient’s chest cavity in order to induce or assist inhalation and exhalation. Accordingly, pressure applied to the chest shell through the outlet conduit 14 will cause collapse of the chest cavity in order to produce exhalation 15 while vacuum pressure in the conduit will expand the chest cavity in order to induce or assist inhalation, pressure and vacuum being established in the outlet conduit cyclically in accordance with the breathing rate. The breathing rate may be preselected or may be regulated 20 in accordance with the natural breathing rate of the patient through the use of a nasal canula or tube 18, one end of which is inserted into a nostril of the patient and held in position by any suitable means as for example the string 20 hooked about the ear of the patient. Any in25 halation by the patient producing a very small vacuum pressure signal will therefore be communicated by the tube 18 to a sensor device 22 electrically connected to the resuscitator apparatus by the electrical cable 24 so as to regulate operation thereof in accordance with the natural 30 breathing rate of the patient.

The resuscitator apparatus is mounted within a housing generally referred to by reference numeral 26 supported by caster wheels 28 so as to facilitate movement thereof. A guardrail 30 is mounted adjacent the bottom of the 35 housing in encircling relation thereto while opposite side walls 32 of the housing are provided with push rod handles 34 for movement of the apparatus. The housing 26 is also provided with a front wall 36 and a top wall 38 having a removable closure panel 40 providing access to the interior of the housing. A key operated lock device 42 may therefore be provided to hold the panel 40 in place.

Mounted on the top wall 38 is a control panel 44 provided with a pair of handles 46. As more clearly seen in 45 FIGURES 1, 2, 4 and 9, the control panel 44 is connected to an enclosure 48 for the electrical control components to be hereafter described. The control panel therefore mounts the various adjustable control devices associated with the control system including a breathing rate selector 5θ 50 by means of which the number of strokes or breathing cycles per minutes may be preselected for one mode of operation of the resuscitator apparatus. A test interval selector 52 is also mounted on the control panel by means of which operation of the resuscitator under the selected _5g breathing rate control may be interrupted after a time interval selected for a predetermined period (5 seconds) during which the sensor device 22 may convert operation of the resuscitator to a natural breathing rate if any breathing action of the patient is sensed. The operational _g0 mode of the resuscitator is selected by the mode selection control 54 while the administration of oxygen may be controlled in accordance with the setting of the oxygen control knob 56. Facilities are also provided for varying the duration of the inhalation period of the resuscitator ₆5 apparatus when regulated at a rate set by the rate selector 50. Accordingly, a tool operated spacer control 58 is provided on the control panel 44 for such purpose. Finally, a pair of neon indicator lamps 60 and 62 are mounted by the control panel providing a visual indication of resusciγθ tator operation. Electrical power for operating auxiliary equipment such as a heater for an atomizer, etc., may also be supplied through an electrical power cable plugged

3,333,581 ³ into the electrical receptacle device 64 mounted on the side wall 32. The side wall also mounts a motor switch 66 adjacent to an exhaust vent 68 through which heat may be dissipated from a pump motor 70 mounted within the housing 26 as more clearly seen in FIGURE 4.

Referring now to FIGURES 1, 2, 3 and 4, it will be observed that the front wall 36 of the housing mounts various valve control devices including a vacuum control knob 72, a pressure control knob 74 and a flow rate control knob 76. Also mounted on the front wall 26 is a tracheal tube connection 78 by means of which oxygen may be administered through a tracheal tube to the nostril or trachea of the patient. The tracheal tube connection 78 is therefore connected to a conduit 80 located within the housing and connected to the outlet of a solenoid control valve 82 having an inlet connection 84 projecting from the rear wall 86 of the housing. A pressure regulated source of oxygen (not shown) may therefore be connected to the connection 84 when oxygen is to be administered. The front wall 36 of the housing also mounts a restrictive suction valve 88 adapted to be connected by the tube 90 to a liquid trap 92 supported on the front wall by the bracket 94 by means of which fluids may be extracted from the patient when deemed advisable.

Mounted within the housing 26, is an air pump mechanism 96 supported in fixed position by being bolted to the cross angle frame members 98 and 100, the pump mechanism being driven by the motor 70 aforementioned which is connected to the pump mechanism housing and projects laterally from one side of the pump mechanism. The pump mechanism has a discharge portion 102 connected by the T-coupling 104 to one of the inlet ports of a three-way valve device 106. The T-coupling 104 is also connected to a pressure control valve 108 through which the discharge pressure of the pump mechanism may be regulated by controllable venting through a downwardly extending exhaust conduit 110 having an outlet end extending below the housing and connected to a restrictive outlet muffler 112. Thus, the pressure control knob 74 connected to the pressure control valve 108 may restrictively open or close the pressure control valve 108 in order to regulate the discharge pressure from the pump mechanism. The pump mechanism is also provided with an inlet connection 114 connected by the elbow 116 to the flow rate control valve 118 to which the control knob 76 is connected for controlling the opening of the valve 118 in order to regulate the volumetric flow rate of air. The flow rate control valve 118 is connected to the T-coupling 120 through which suction pressure is applied to an inlet port of the three-way valve device 106. Accordingly, the valve device 106 is provided with two inlet ports for respective connection to the regulated pressure discharge of the pump mechanism 96 and the suction inlet of the pump mechanism. The valve device 106 is provided therefore with a common outlet 122 connected by the coupling 124 to the outlet conduit 14. Accordingly, regulated discharge pressure from the pump mechanism 96 and inlet suction pressure are alternatively applied to the outlet conduit 14. The inlet suction or vacuum pressure is regulated by the vacuum control valve 126 connected to the T-coupling 120 and restrictively open under control of the control knob 72 for drawing a fresh supply of air through the intake conduit 128 extending downwardly from the vacuum control valve 126 to the bottom of the housing. The valve device 106 is therefore actuated so as to establish fluid communication between the common outlet 122 and the two inlet ports respectively exposed to regulated discharge pressure and regulated vacuum pressure. Movement of the valve device 106 between its operative positions is effected in a cyclic manner by means of an oscillating motor 130 mounted on top of the valve device. The pressure in the common outlet of the valve device is indicated by the pressure gauge 132 mounted on the front wall 36 of the resuscitator housing. The restrictive suction valve 88 is also connected by the suction line

134 to the elbow 116 so as to supply suction pressure to the liquid trap 92 when the valve 88 is open.

Successful operation of the resuscitator depends in large measure upon the ability of the sensor device 22 to sense a relatively small pressure variation occurring as a result of inhalation by the patient. Referring therefore to FIGURES 5, 6, 7 and 8, it will be observed that the sensor device includes a pair of parallel spaced housing sections 136 and 138 interconnected in spaced relation by a plurality of fastener assemblies 140. An inlet tube connector 142 is received within the housing section 138 so as to establish fluid communication between the tube 18 and a passage 144 which opens into a pressure sensing chamber 146 formed by the housing section 138 on one side of a flexible diaphragm 148. The diaphragm 148 is secured at a circumferentially outer portion to a stepped annular shoulder 150 formed on the housing section 138 between the chamber 146 and the radially outer annular surface 152 through which the fastener assemblies 140 extend. The inlet connector 142 is also provided with a connecting portion 154 received within the housing section 136 for communication with the passage 156 formed therein. The passage 156 communicates with a pressure sensing chamber 158 formed on one side of the diaphragm 160 secured to the annular shoulder portion 162 of the housing section 136. The housing section 136 is therefore also provided with a radially outer annular portion 164 through which the fastener assemblies 140 extend. Also extending between the radially outer portions 164 and 152 of the housing sections, opposite the inlet connector 142, is a spring element 166 reacting between brass terminal pin 168 and an externally threaded sleeve 170 through which a brass pin 172 extends. An electrical connector 174 is mounted about the brass terminal pin 172 so as to establish electrical connections between the terminal pins 168 and 172 through the electrical cable 24 extending from the sensor device to the resuscitator apparatus.

The diaphragms 148 and 160 are maintained in spaced relation to each other by a pair of spacer members 176 and 178 separated by an annular O-ring 180 having a gap 182 so as to maintain the space between the spacer members under atmospheric pressure. Vacuum pressure applied to the pressure sensing chambers 146 and 158 will accordingly cause displacement of the diaphragms away from each other opening the electrical contact otherwise established between contact assemblies 184 and 186 respectively mounted centrally of the diaphragms 148 and 160, the contact assemblies being movable through alined openings 188 and 190 in the spacer members. The contact assembly 184 includes an externally threaded conductive screw member 192 having a slotted adjustment end for receiving a screw driver inserted through a central opening in the housing section 138 when the nut 194 is removed. The contact screw 192 is therefore threadedly received within a nonconductive button 196 on one side of the diaphragm 148, a washer 198 being provided on the other side and held in assembled position by a clip 200. A gold leaf foil strip 202 is mounted on the diaphragm 148 establishing a current carrying path from the conductive screw element 192 to a silver pin 204 electrically connected to the terminal pin 172. The conductive screw element 192 is therefore adapted to engage and establish electrical contact with the gold plated silver pin 206 in the contact assembly 186. A light-weight button 208 holds the pin 206 on one side of the diaphragm 160, the pin 206 extending through a washer 210 on the other side of the diaphragm 160 and held assembled thereon by the clip 212. A gold leaf foil strip 214 is mounted on the diaphragm 160 and establishes a current carrying path from the pin 206 to a silver pin 216 connected to the brass terminal pin 168. It will therefore be apparent, that the contact assemblies 184 and 186 will establish an electrical connection which is opened in response to the sensing of inhalation or a relatively low vacuum pressure

3,333,581 in the pressure sensing chambers 146 and 158 communicating with the nostril of the patient through the tube 18.

Operation of the resuscitator apparatus may be reviewed with reference to FIG. 10. It will therefore be recalled, that regulated discharge pressure from the pump 96 and regulated vacuum pressure from the vacuum control valve 126 is alternatively applied to the outlet conduit 14 through the three-way valve 106 in a cyclic manner by operation of the oscillating motor 130. Operation of the oscillating motor 130 is therefore regulated by a cycle control component 218. Also, energization of the solenoid valve 82 for administering oxygen from any source 220 at a pressure regulated by the regulator valve 222 may be effected through the oxygen control component 224 as a result of which oxygen may be supplied to the patient either continuously or during the inhalation portion of each cycle as regulated by the cycle control 218. Referring therefore initially to FIGURE 11, the control system through which the cycle control 218 is operative to regulate the cycling of the oscillating motor 130, is diagrammatically illustrated. The control system is therefore provided with a mode control component 226 the setting of which is selected by manipulation of the mode selector 54 aforementioned in order to establish one of three different operational modes for the resuscitator apparatus. When the mode control is set for continuous operation, as indicated by line 228, the relay 230 is operated so as to energize a signal generator 232 dispatching cycling control signals to the cycle control 218 by means of which the frequency of the oscillating motor 130 is regulated in order to induce breathing at a preselected rate. Thus, the output frequency of the signal generator 232 is selected by the frequency control 50. The resuscitator apparatus in this mode of operation will therefore be regulated at a preselected frequency to the exclusion of any other regulation. When however, the mode selector 54 is set to a controlled position as depicted by line 234, the sensor device 122 is rendered operative so as to regulate the cycling signal dispatched by the cycle control 218. The output signal from the sensor 22 is supplied to the cycle control 218 by the line 236. When the sensor 22 is operative to regulate the cycling frequency, the signal generator 232 will be inoperative inasmuch as the relay 230 will not be energized. Thus, the operational modes represented by lines 228 and 234 respectively effect cycling at a preselected rate through the signal generator 232 and at a natural rate as sensed by the sensor 22 to the exclusion of any other regulation. Automatic operation is effected when the mode selector 54 is set to an automatic position as depicted by the line 250 in FIGURE 11. Under automatic operation, the loss of a signal output from the sensor 22 is operative on the demand control 240 to supply an operating signal by line 252 to the relay 230 through which operation of the signal generator is initiated and the sensor disabled. However, a signal is also supplied through line 254 to the interval control component 248 which then periodically dispatches of a signal through line 256 to the disabling switch 258 interrupting energization of the relay 230 and regulation under control of the signal generator 232. Accordingly, the disabling signal in line 242 is also removed so as to permit the sensor 22 to regulate cycling if any inhalation of the patient is sensed during the interruption period effected by the interval control 248. If inhalation is sensed by the sensor 22, the signal in line 238 applied to the demand control 240 will prevent cycling regulation by the signal generator 232. Should however, natural breathing cease, no signal will be dispatched by the sensor 22 to the line 238 so that the demand control 240 will once again supply a signal in line 252 in order to resume operation under control of the signal generator 232.

Referring now to both FIGURES 12A and 12B, one form of electrical circuitry corresponding to the control system depicted in FIGURE 11, is shown. The power supply shown in FIGURE 12A includes therefore, a pair of powerlines 260 and 262 connected to a 115 v. AC electrical source for energizing the primary 264 of a main power transformer 266 when the power switch 268 is closed. Also, upon closing of the motor switch 66, the pump motor 70 is energized together with the parallel connected primary 270 of transformer 272 through which the oscillating motor 130 is energized. The secondary 274 of the transformer 272 is therefore connected by a line 276 to one terminal of the motor 130 and by line 278 to the cycling control switch 280 of the cycle control 218 as shown in FIGURE 12B in order to reverse energization of the motor 130. The cycling control switch 280 is therefore oscillated between contacts 281, 283 and 285, 287 by pulsing of the power relay 282. Contacts 281 and 283 are respectively connected to motor 130 and the automatic contact 284 of selector switch 56 so that the cycling switch 280 may switch the oscillating motor 130 and at the same time deenergize the solenoid valve 82 when the selector switch 56 is in an automatic position engaging contact 284. Accordingly, during the inhalation period the solenoid valve 82 will be deenergized and open so as to supply oxygen to the patient, the valve being closed during the exhalation portion of the cycle by energization of the solenoid valve through the cycling control 218. When however, the selector 56 is in the continuous position engaging the contact 286 no energizing circuit can be completed for the solenoid valve 82 so as to maintain a continuous supply of oxygen. One terminal of the solenoid valve 82 is therefore connected to line 276 from the secondary 274 of transformer 272, and the other , terminal connected to selector switch 56. When the selector 56 engages the off contact 288 which is connected to line 278 of secondary 274, the solenoid valve 82 will remain energized continuously so as to cut off the supply of oxygen. The transformer 266 is also provided with a plurality of rectifier circuits 290 associated with a plurality of secondary windings providing rectified voltages of different values as indicated in FIGURE 12A to the various components of the electrical circuitry depicted in FIGURE 12B.

It will be observed in FIGURE 12B, that the power relay coil 282 of the cycle control 218, is pulsed by an amplifier output signal appearing at the collector of the second stage amplifier transistor 292. The emitter of the transistor 292 is connected to the +30 volt source of the power supply 290 producing an energizing current in the power relay 282 when a signal is applied to the base of the transistor biased through bias resistor 294 connected to the +24 volt source of the power supply. The signal applied to the transistor 292 is derived from the collector of the first’stage amplifier transistor 296 having an emitter connected to the +36 volt source of the power supply. The base of transistor 296 is biased through resistor 298 connected to the +30 volt source and the resistor 300. The transistors 296 and 292 are therefore operative to amplify an input signal supplied to the base of the transistor 296 from either line 302 or line 304.

The signal input line 302 is connected to the sensor 22 through the normally closed relay sensor switch 305 and line 306. Accordingly, upon closing of the contact assemblies in the sensor 22, an input voltage is established in line 302 derived from the 42 volt source connected to the sensor by line 308 and the voltage reducing resistor 310. This voltage signal will therefore occur during the exhalation portion of the cycle sensed by the sensor device 22 in order to supply cycling pulses to the component 218 at the natural breathing rate. Alternatively, pulsing of the power relay 282 may be effected by signal voltage supplied by line 304 to the amplifier stages. The voltage signal appearing in the line 304 is however, regulated in accordance with a selected frequency output of the signal generator 232.

The signal generator 232 is in the form of a flip-flop

3,333,581 circuit connected to the +85 volt source through potentiometer 312 when the normally open relay input switch 314 is closed. A reduced voltage is then supplied through the inhalation spacer potentiometer 58 to a resistance divider network and through the potentiometer setting of the frequency control 50 establishing reduced differential voltages of a regulated value on opposite sides of the storage capacitor 316 cousing it to charge and discharge at a regulated rate as the neon lamps are triggered on and off. Accordingly, the storage capacitor 316. is connected between the signal output line 304 and line 318 to establish a conductive path either through the neon lamp 62 or the neon lamp 60 in series with resistor 320, the neon lamps being interconnected with a common return line 322 connected to the —85 volt source. The capacitor 316 is charging and discharging at a controlled rate with alternatively supply voltage signals, in output line 304 as aforementioned. The shunt connection through resistor 324 is closed by the normally closed relay rate switch 326 so as to maintain capacitor 316 in a completely discharged state. It will therefore be apparent, that when the relay coil 330 is de-energized, the normally open relay switches 314 and 328 and normally closed relay switch 326 will maintain the signal generator 232 inoperative. As long as the relay coil 332 is de-energized at the same time, the normally closed relay switch 305 will maintain the sensor 22 operative to regulate the cycling pulses applied to the component 218.

When the mode selector 54 is displaced to the position for continuous mode of operation, clockwise from the position illustrated in FIGURE 12B, an electrical connection is established from the +15 volt source through line 334, switch 336, resistance 338, line 340, switch 342, line 344 and normally closed energizing relay switch 346 to the base of transistor 348. The base of the transistor is biased through bias resistor 350 by the +36 volt source so that the voltage signal applied thereto will render the transistor conductive in order to establish a conductive path from the +30 volt source through line 352, the emitter and collector of the transistor 348, to the relay coil 330 connected to the zero voltage line 354. Also connected in parallel with relay coil 330 to the collector of transistor 348, is the relay coil 332 also connected in common with the zero voltage line 354. It will therefore be apparent, that relay coils 330 and 332 will be simultaneously energized so as to open the sensor relay switch 305 disabling regulation by the sensor and actuating the realy switches 314, 326 and 328 in order to place the signal generator 232 into operation. Cycling of the resuscitator apparatus will then be effected at a selected rate determined by the setting of the potentiometers associated with the frequency controlling control knob 50. The setting of the spacer potentiometer 58 on the other hand, is made infrequently in order to vary the duration of the inhalation portion of the breathing cycle.

When the mode selector 54 is in the automatic position illustrated in FIGURE 12B, no voltage is directly available from the +15 volt source for supply to the line 340 in order to trigger the transistor 348 into a conductive state for energizing the relay coils 330 and 332 as aforementioned in connection with the continuous mode of operation. Instead, signal voltage for triggering the transistor 348 into its conductive state is supplied to line 340 from the demand control circuit 240 and periodically interrupted by the test interval timer 248 at periods determined by the setting of the potentiometer control 52 by energization of the relay coil 356 opening the normally closed relay switch 346 in order to remove the signal voltage from the base of transistor 348 switching it to its nonconductive state. The interval control component 248 is rendered operative to function under the automatic mode of operation inasmuch as the switch 336 then connects the +15 volt line 334 to the emitter of transistor 358 through line 360. With relay coil 330 energized, the interval relay switch 362 is actuated so as to remove the 15 volts applied to one side of the capacitor 364 while at the same time connecting the base of transistor 358 thereto. The voltage supplied to the base of transistor 358 will therefore be applied through a resistance divider network and the potentiometer 368 from the capacitor 364 through the resistor 366 in series therewith in order to control the discharge rate of capacitor 364 and the operation of relay 356. The capacitor 364 when discharging does so at a rate regulated by the interval control potentiometer 52. Accordingly, the charge on capacitor 364 will decrease until a trigger voltage value appears on the base of transistor 358. When triggered, the transistor 358 will conduct energizing current to the relay coil 356 through line 370, the relay coil 356 being connected to the zero, voltage line 354. Accordingly, the relay coil 356 will actuate relay switch 346 to deenergize the relay coils 330 and 332. Upon deenergization of the relay coils 330 and 332, operation of the system will change from regulation by the signal generator 232 to regulation by the sensor 22 if it is sensing inhalation of the patient. Also, relay switch 362 will reset the test interval control 248.

When operating in automatic mode either from signal generator 232 or sensor 22, transformer 380 connected by its primary 378 to the relay 282, supplies a pulse to the charge capacitor 39© and thereby triggers transistor 374 into conduction. The secondary 382 of transformer 380 is therefore connected by the full wave rectifier 384 across the charge capacitor 390. The base of transistor 374 during the automatic mode of operation is therefore connected to one side of the full wave rectifier through switch 386 in the mode control while the emitter is connected through the voltage driving resistor 391 to the 42 volt source. The output of the transistor 374 is conducted from the collector through the load resistor 376. The base and emitter are also maintained at a predetermined potential difference by the resistor 393 so that the trigger pulse from the capacitor 390 applied through the potentiometer 392 may trigger the transistor 374 into conduction.

When the signal generator 232 is operating, relay switch 372 is open and transistor 394 conducts because of the voltage established on its base by the 24-volt source through resistors 395 and 389 in series. The emitter of transistor 394 is therefore biased by a voltage established through potentiometer 400 interconnected between the 30 and 36 volt sources. A voltage is thereby established on the base of transistor 396 through resistor 396 which causes it to conduct and maintain a signal in line 340. The signal in line 340 holds transistor 348 conductive and relays 330 and 332 energized so that the signal generator 232 is in an operating condition. When the test interval control 248 operates as previously described, relay switch 346 is opened removing the signal in line 340 from transistor 348. Operation is thereby returned to control by sensor 22. As a result thereof, relay switch 372 is closed so that a charge accumulated on capacitor 388 drives transistors 394 and 396 into a non-conducting state, removing any control signal from line 340. The timing capacitor 388 is charged each time relay 282 operates because of a pulse transferred thereto through the transistor 374 rendered conductive as hereinbefore indicated. If the relay 282 continues to operate indicating that the patient is attempting to control the resuscitator through the sensor 22, the timing capacitor 388 will be maintained in the charged condition and no signal will be developed by transistors 394 and 396. However, if the relay 282 fails to operate for as long as five seconds, the charge on the timing capacitor 388 will be drained off through resistor 389 thereby driving transistors 394 and 396 into a conducting state and establishing a signal on line 340 to operate transistor 348 and transfer control of the resus

3,333,581 citator back to the signal generator 232. The foregoing cycle will repeat itself.

From the foregoing description, the construction, operation and utility of the resuscitator apparatus and control system associated therewith will be apparent. It will therefore be appreciated that the resuscitator is capable of being regulated to provide the proper pressure and vacuum levels for the chest shell 16 in order to induce or assist the patient with breathing. The operational mode of the resuscitator may also be varied for continuous operation at a controlled breathing rate or at a natural breathing rate by use of the low pressure sensor device 22. Automatic operation of the resuscitator may also be effected so that the breathing rate may be controlled and periodically during a test interval of preselected duration, the signal generator regulating the cycling rate, is temporarily disabled to permit the sensor to take over regulation at the natural breathing rate if the patient is breathing. Should the sensor device fail to detect any breathing on the part of the patient, after the test interval has elapsed, operation is resumed under regulation of the signal geneerator.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.