US3414896A - Respiratory monitor - Google Patents

Description

Dec. 3, 1968 R. v. GLICK ET AL RESPIRATORY MONITOR 2 Sheets-Sheet 2 Filed Jan. 5, 1965 Mud: I30 I \D o ma R U N E 0 E M T 8 mm Z c BUZZER l R m Mm Mm Q n KWwM v 0 2w a w m flmw a L D w United States Patent 3,414,896 RESPIRATORY MONITOR Roy Victor Glick, White River Junction, Vt., and James D. McNeal, North Haven, and Anthony P. Costanzo, New Haven, Conn., assignors, by direct and mesne assignments, to Monitor Instrument Company, New Haven, Conn., a corporation of Connecticut Filed Jan. 5, 1965, Ser. No. 423,532 13 Claims. (Cl. 340309.1)

ABSTRACT OF THE DISCLOSURE A monitoring apparatus for a respirator having indicating means responsive to the operation of the respirator, the indicating means comprising first means for indicating the inhalation and exhalation states of the respirator, and second means for measuring the length of time said first means is in either of said states, the improvement characterized in that the second means includes a series connection of an ampere meter, a capacitor and switching means connected in parallel with said capacitor for permitting said capacitor to charge and discharge in response to the operation of said first means.

This invention is directed to ventilation or respiratory apparatus and more specifically to a monitoring apparatus which is particularly suitable for use in conjunction with pulmonary respirators.

During periods of hospitalization or emergency, patients often require that mechanical means be utilized to assist the normal respiratory processes. This is particularly important when a patient is undergoing anesthesia. Also, a pulmonary ventilator or respirator may be utilized with a patient who has undergone a tracheotomy operation or is receiving intensive care. In all of these cases, the patient is not usually able to control his own respiratory processes. Generally both the inhalation and exhalation phases of the ventilation or respiration cycle of the patient must be controlled by adjusting a respiratory apparatus itself. A respirator apparatus is generally defined as a device for maintaining artificial respiration.

Generally, control of respiratory apparatus has been a function of timings, made by an attendant with the help of a watch. The ratio of the inhalation to exhalation phase time has been monitored in a similar manner, as well as the total respirations per minute. Due t the lack of precise monitoring apparatus for use in conjunction with respirators, accurate control of the inhalation and exhalation phase time as well as respirations per minute is not readily attained. Further, unless a private nurse is on duty, the difiiculites of a patient in breathing is generally not determined until the next round by the nurse On duty.

For these reasons, applicants have provided a new and improved monitoring apparatus which aids nurses and doctors in treating and attending a patient who requires continuous assistance in breathing.

Accordingly, it is the principal object of this invention to provide a new and improved respirat ry monitoring apparatus.

Another object of this invention is to provide a monitoring apparatus which will warn of respiratory failure or difliculty encountered by a patient whose breathing is controlled or regulated by a mechanical respirat r.

A further object of this invention is to provide a new and improved monitoring apparatus which can serve as a set-up and tune-up device aiding in optimum adjustment of the controls of a respirator.

Other objects and many of the attendant advantages of this invention will be readily seen and appreciated as "ice the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof, and wherein FIG. 1 is a diagrammatic view of a respiratory and monitoring apparatus according to this invention;

FIG. 2 is a schematic diagram of the respirator apparatus according to the instant invention; and

FIG. 3 is a schematic diagram of an alternate embodiment of the respiratory monitoring apparatus according to this invention.

A respirator with which the invention may be practiced may be of the Intermittent Positive Pressure Breathing type, such as that sold by the Bird Corporation of Palm Springs, California, Models Mark VII or Mark VIII. The intermittent type of respirator provides air or gas to the patient on a non-continuous basis, that is, n the inhalation phase of respiration to inflate the patients lung. The Bird Mark VII model type of respirator, generally shown at 11, has two outlet tubes indicated at 12 and 14 emanating from it. The Bird Model Mark VIII has three tubes emanating from it, the third one used to pr duce negative pressure on the exhalation phase of respiration and, accordingly, is not described since the tube is not common to both Bird Model types of respirators. This monitor is suitable for use with both types of Bird respirators or with other intermittent types of respirators. In both cases the monitor tube is attached to the tube that has gas under pressure in it during the inhalation phase of respiration. This outlet tube is indicated at 12. The function of the tube 12 is to drive the micronebulizer 13 and close the exhalation valve 15 during the inhalation phase of the cycle. Pressure in tube 12 on the inhalation phase of respiration cycle exceeds approximately 4 psi. but generally does not exceed 50 psi. When tube 12 enters the micronebulizer 13 the pressure of the gas in the tube is reduced to a range of about 5-60 C. water pressure and is added to the flow of gas coming through tube 14 from respirator 11. The tube 14 is the major source of air or gas which is provided to the patient. The combination of gas or air from tube 14 and from tube 12 is then fed through tube 14 through the valve 15 and then through a tube 18 to the patient. The valve 15 directs the gas flow to the patient and permits the patient to exhale upon the completion of the inhalation cycle. The micronebulizer 13 is a device which produces a medication aerosol mist by the action of the gas in the high pressure tube 12 and a reservoir of medicant fluid. It is to be understood that this monitor is capable of operating in conjunction with other types of respirators, as long as it is coupled to a tube which exhibits a change in pressure during either the inhalation or exhalation phase of the respiration cycle.

The monitoring device of this invention is coupled to the respirator 11 by a T-configuration connection 16 which is inserted in the tube 12. T-connection 16 as shown is coupled through a tube 17 to a pressure sensitive device indentified by reference numeral 34. Device 34 may be of the bellows type pressure sensitive switch. Pressure sensitive device 34 indicates the pressure of the gas or air in tube 12. During the inhalation phase, device 34 indicates that gas at a predetermined pressure is flowing through tube 12 and during the exhalation phase indicates that gas below a predetermined pressure is present in tube 12.

The monitoring apparatus shown at 19 is provided with time-indicating meters 20, 21 and 22. Indicating meter 20 provides the time length of the exhalation phase, meter 21 provides the time interval of the inhalation phase, and meter 22 indicates the number of respiratory ventilation cycles per minute. Associated visual indicators such as lights 24 and 25 are provided on monitoring apparatus 19 to indicate when the respirator is in the inhalation or exhalation phase of the ventilation cycle. A light 23 is provided on the apparatus for indicating that the power is being applied to the apparatus as, for example, from a wall outlet. Switch 27 is incorporated in apparatus 19 to connect or disconnect an audible alarm 70 shown in FIG. 2, which indicates when either the inhalation or exhalation phase has exceeded a, predetermined time limit.

Additionally, visual indicator 26 is provided to show when the inhalation or exhalation phase has exceeded a predetermined time limit and visual indicator 28 is provided to indicate when the patent is breathing at a critical- :ly high or critically low ventilation rate.

Coupled to monitor 19 is a remote indicator 29 connected by means of a multi-conductor line 29a. Visual indicating devices shown as 24a, 25a, 26a and 28a, represent lights which are connected in parallel with corresponding lights 24, 25, 26 and 28 of apparatus 10. Thus, a patient who is undergoing intensive care can, by the use of this remote indicating mechanism 29, be constantly monitored from a central location such as the nurses duty station (desk). A schematic diagram of the monitoring apparatus embodying the invention is shown in FIG. 2.

As indicated on the drawing by Roman numerals, the monitor comprises first circuit means for indicating inhalation and exhalation portions of a ventilation cycle at I. Roman numeral II indicates a means for determining the time of the inhalation and exhalation portions of a ventilation cycle. Roman numeral III shows a means for warning of breathing difiiculties encountered by a patient. Roman numeral IV shows a circuit means for providing direct current, and Roman numeral V indicates a circuit for presenting the ventilation rate per perdetermined time interval.

Power, which may be derived from a readily available source, is applied to monitor 19 through a transformer 30 having a primary winding 31 and secondary windings 32 and 33. Winding 32 steps up the primary voltage while winding 33 steps down the primary voltage.

Pressure sensitive device 34 comprises, in a preferred embodiment, a double-pole, single-throw pressure sensitive switch. The switch arm 35 is arranged to contact either of terminals 36 and 37. During the exhalation phase of a respiratory cycle when the respirator is not operating, switch 34 will be in a position such that arm 35 is coupled to pole 37. During the inhalation phase of a respiratory cycle, arm 35 of switch 34 will switch to terminal 36. The switch in this position indicates that gas is flowing through tube 12 at greater than a predetermined pressure. In circuit with terminal 37 are, a coil 42a of relay C which operates a normally closed contact 42b, visual indicating means 24, and a time delay relay TD1 in series with a resistor 41. The indicating means provides a signal when the respirator apparatus is in the exhalation phase of the ventilation cycle. The time delay relay which includes a heating element 400, may be of the type which comprises a bimetallic element which, after being energized for a predetermined period of time, heats up and moves in a direction to close contact 4017. Time delay relay TD1 indicates when the respirator has been in the exhalation phase of the ventilation cycle more than a predetermined time, for example, fifteen seconds. Fifteen seconds represents the normal medically allowable time for either the exhalation or inhalation phase of a respiratory ventilation cycle.

The inhalation measuring portion I of the circuit includes a second relay CR having a winding 47a which controls normally closed contact 4712 when arm 35 of switching apparatus 34 is closed on pole 36 and relay CR is energized. Light 25 is connected in parallel with relay winding 47a for visually indicating when the respirator and the patient are in the inhalation phase. A second time delay relay TDZ, having its heating element 45a in series with a resistor 46 is connected in parallel with relay coil 47a and light 25. Time delay relay TD2 indicates when the pressure sensing switch 34 is in an inhalation phase for a predetermined time, as for example, fifteen seconds. When this occurs, time delay relay heating element 45a will close a normaly open contact 45b.

Further, a relay R having a winding 480, an axis 481) and terminals 48c and 48a, is connected in parallel with time delay relay 45a, relay coil 47a and light 25. Arm 4815 will move back and forth between terminals 480 and 48a to indicate when arm 35 of switching device 34 is coupled to pole 36. The operation and function of relay R including arm 48b and terminals 480 and 48d is hereinafter more fully described.

Secondary winding 33 of transformer 30 is coupled to a full wave rectifier 50 which includes a bridge network of four diodes, 51a, 51b, 51c and 51a. The bridge network is connected in parallel with a filtering capacitor 52. Connected as a load to the full wave rectifier circuit are two meter networks 20 and 21.

The first meter network includes ampere meter 20, such as of the galvanometer type, for providing an indication of the time of the exhalation phase of a respiratory ventilation cycle. In series with meter 20 is a resistor 53 and a capacitor 54. Coupled in parallel with capacitor 54 is normally closed contact 42b of relay C. Also connected in series to rectifier circuit 50 is a second ampere meter 21 for indicating the inhalation phase time of a respiratory ventilation cycle. In series with meter 21 is a resistor 56 and a capacitor 57. In parallel with capacitor 57 are normally closed relay contacts 47b of relay CR. Each of meters 20 and 21 is constructed such that the scales indicate zero time for maximum current flow and increasing time for decreasing current flow therethrough.

The inhalation and exhalation times of the respiratory ventilation cycles are obtained in the following manner. When gas at greater than a predetermined pressure flows in tube 12, FIG. 1, the pressure switching device 34 responds and its movable arm 35 is switched to terminal 36. This causes a current through relay coil 47a, through light 25 and relay coil 48a. The current through relay coil 47a causes normally closed contact 47b to open. When contact 47b is in the closed position, meter 21 indicates zero time and maximum current since the meter scale is reversed, that is, for full current through meter 21 the meter time will read zero. The magnitude of the maximum current is primarily determined by the value of resistor 56. Upon the opening of contact 47b, capacitor 57 will begin to charge exponentially. The current through meter 21 will initialy continue to flow at the maximum value and will then exponentially decrease as capacitor 57 charges. Thus, as the current through the meter decreases, the meter indicator will move in the direction of increased time on the meter scale. Otherwise stated, as the current through the meter decreases, the time of the inhalation phase represented on the meter will increase. If, after a predetermined time, the switch 34 is still in the inhalation phase position, for example, after fifteen seconds has elapsed, the time delay relay heating e'ement 45a wil lheat up sufiiciently to close contact 45b. The function of contact 45b is hereinafter described.

Assuming now that the inhalation cycle is completed, pressure sensing switch 34 will detect that there is substantially less gas pressure in tube 12 and therefore arm 35 will move over to pole 37. Relay CR is de-energized, contact 47b closes and meter 21 once again indicates zero time. When switch 34 is in the exhalation position, light 24 will so indicate, and relay coil 42a will open up normally closed contact 42b to permit capacitor 54 to charge up to the supply voltage. Meter 20, which presents exhalation time, will indicate zero time for this maximum current flow condition. After opening the normally closed contact 42b and permitting capacitor 54 to begin charging, the current through meter 20 will initially remain at the maximum value and will then exponentially decrease as time goes on. Meter will indicate this change by having its pointer move to indicate the increasing time of the exhalation phase. Further, time delay relay heating element 40a will indicate when the exhalation phase has exceeded a predetermined time period as, for example, fifteen seconds. This will close the normally open contact 40b. The functions of the normally open contact 40b are hereinafter described.

The metering circuit described will indicate and visually present the times of the inhalation and exhalation phases of a ventilation cycle. This is accomplished by opening normally closed contacts which are in parallel with and short circuit a capacitor, thus permitting current to flow into the capacitor and thereafter decay at an exponential rate. The exponential decay of current is indicated by a meter which has its scale adapted to read zero when there is maximum current flow and increasing time for decreasing cur-rent flow. That is, increased time of capacitor charge is an indication of decreasing current flow.

Also coupled to the secondary winding 33 of the transformer is a normally open contact 6817 in series with a light 28. In parallel with contact 68b and light 28 is the parallel combination of the two normally open time delay contacts b and b. This combination is in series with a second parallel combination of light 26 and a series circuit of switch 27 and an audio signal device such as buzzer 70. Assuming that with switch 27 is closed and that one of the time delay heating elements 40a or 45a has been energized in the circuit for a suflicient period of time which indicates that the exhalation or inhalation phase of the ventilation cycle has exceeded a predetermined time limit, one of normally open contacts 40b or 45b will close. This will provide a current through light 26 and energize buzzer 70. This indicates to an attendant that the patient utilizing the respirator is encountering breathing ditficulties during either the inhalation or exhalation phase of the ventilation cycle. The function of normally open contact 68b and light 28 will be hereinafter described.

Connected to the step-up winding 32 of transformer 30 is a full wave bridge rectifier network 71 which includes four diodes 72a, 72b, 72c and 72d. A filter and voltage regulator circuit which comprises a capacitor 73, resistor 74, gas tube 75, resistor 76 and capacitor 77 is connected to the bridge network 71. Resistance network comprising resistors 78 and 79 are connected across the filter and regulating circuit. Connected to the high voltage side of resistor 78 is terminal 48d of relay R. Connected between the low voltage side of resistor 79 through capacitor 60 and resistor 69 is arm 48b of relay R. Also connected to the low voltage side of resistor 79 is ampere meter 22 and resistor 61 coupled to terminal 480 of relay R. Ampere meter 22 is provided with an electrical conducting pointer 65 and two end-of-scale meter contacts 66 and 67 which are adjustable along the scale of the meter.

Coupled across meter 22 is a range adjusting potentiometer 63 for controlling the current flow through meter 22. Connected in parallel with the metering circuit which comprises resistor 61 and meter 22 is capacitor 62. Coupled to the connection of resistors 78 and 79 is relay winding 68a of relay K. Relay winding 68a is connected to the end-of-scale meter contacts 67 and 66 of meter 22 and meter pointer 65 of meter 22 is connected to the low voltage side of resistor 79. As mentioned previously, the meter contacts shown as 66 and 67 of meter 22 are positionable on the meter scale of meter 22, for example, contact 66 could be manually positioned close to the end of the meter range of meter 62 and contact 67 could be manually positioned at the other end of the meter scale. When pointer 65 of meter 22 reaches either of the prepositione-d meter contacts, the circuit is closed and a cur-rent will flow through coil 68a to close contact 6817. This causes a current to flow through light 28 which gives notice that the ventilation rate of the patient is either too high or too low.

The operation of this portion of the circuit which provides an indication of the number of ventilations per minute is as follows: when the pressure sensing switch 34 has its arm 35 closed on pole 36, relay coil 48a will cause arm 48b which is in the normally closed position to switch over to pole 480. When arm 48b is closed on pole 48d, capacitor 60 charges toward the voltage provided by the bridge and regulating network. Upon switching of arm 48b to pole 48c, capacitor 69 is placed in circuit with capacitor 62 which then begins to charge to the voltage to which capacitor 60 has previously charged. Furthermore, cur-rent flows through meter 22 as the number of inhalation and exhalation phases of the ventilation cycle continue to move arm 48b back and forth from poles 48c and 48d. During this time, capacitor 62 will continue to charge until it reaches a predetermined equilibrium, that is, when the voltage stored in capacitor 62 is equal to a predetermined portion of the voltage stored by capacitor 60. At this time, the current flow through meter 22 will stabilize and the meter then will read a constant number of ventilations per minute or predetermined period of time.

It is believed that the basis of this rate of ventilations measurement is that the current flowing through meter 22 is related to the number of times per minute or other predetermined time that arm 48b makes contact with the contacts 480 and 48d. This is in turn related to the quantity of electricity or charge stored in the capacitor 60 when the arm 48b is positioned on contact 480 and the quantity of electricity or charge stored in the capacitor 62 during the time that the arm 48b is positioned on the contact 48d. Since the quantities of charge transferred between the capacitors are substantially equal and since the current flowing in meter 22 is related to the charge stored in the capacitors, the current flowing through the meter is therefore representative of the ventilation rate.

If the patient or the respirator fails to continue in the same repetitive manner as, for example, the number of ventilation cycles per predetermined time either decreases or increases, the current through meter 22 will decrease or increase in the same manner and the number of ventilations per minute will vary since there will no longer be the predetermined equilibn'um between the voltages on capacitors 60 and 62. If the ventilations per minute reach too low a lovel as, for example, ten ventilations per minute, the pointer 65 will close on contact 67, current will flow through coil 68a and close normally open contact 68b. Light 28 will then be illuminated to indicate that the patient is breathing at too low a ventilation rate.

In the aforementioned manner, applicants have provided a respirator monitoring apparatus which will indicate the time of both the inhalation and exhalation phases of the ventilation cycle, the number of ventilations or ventilation rate, as well as indicating a critically low or high ventila tion rate.

Furthermore, applicants have provided a monitoring apparatus which indicates either by audible signals or visual means the inhalation and exhalation phase times, critically high or low ventilation rates and failure of the respirator or the patent to properly function. Additionally, applicants device can be utilized for remote observation when used in conjunction with remote "visual indicator 29. The four visual indicators, 24a, 25a, 26a and 28a, are coupled in parallel as shown in dotted lines in FIG. 2, across lights 24, 25, 26 and 28.

While it will be understood that the circuit specifications may vary according to the design for any particular application, by way of example only the following circuit specifications are included for the circuit of FIG. 2:

Capacitors 54 and 57 microfarads 200 Meters 20 and 21 milliamperes -.1 Resistors 53 and 56 ohms 6000 Capacitor 6t microfarads 2 Resistor 69 ohms 1000 Resistor 61 do 5300 Meter 22 milliamperes 0.1 Resistor 63 ohm trimpot 25,000 Capacitor 62 microfarads 6500 The remainder of the circuitry is conventional in nature and can be determined from the above circuit values. Meter 22 may be of the type sold by Simpson Meter Company, Model 29 XA, and time delay relays 40a and 45a in conjunction with their respective contact elements 40b and 45b may be of the type known as Thermal Time Delay Relays sold by Amperite Company, Inc., of New York.

It is to be understood that the metering apparatus disclosed herein can be utilized for other types of Intermittent Breathing respirators as, for example, the Bennett type of respirator. Further, if it is desired to use the present invention in conjunction with the volume type respirators, the pressure switch disclosed herein could 'be replaced by a volume measuring switch without departing from the scope of this invention.

Referring now to FIG. 3, there is shown an alternate embodiment of the circuit shown in FIG. 2, only those components in FIG. 3 which have been modified are given different numerals. The portion of the monitor circuit I has been altered by including a double-throw, double-pole multiple contact relay P having a coil 100. The relay P and its associated contacts 100a and 100]), arm 1002 and poles 100] and 100g takes the place of the relays C, CR and R of FIG. 2. When the arm 35 of pressure sensitive switch 34 is positioned on contact 37, relay contact 100a will be normally open to allow capacitor 54 to charge and at the same time contacts Gb will be normally closed, thereby preventing capacitor 57 from charging. Further, arm 100e will be positioned on pole 100] to allow the capacitor 60 to charge. When the arm of switch 34 moves to contact 36, contact 100a will close and contact 1001) will open, thereby allowing capacitor 57 to charge and discharging capacitor 54. Additionally, arm 100:: will be positioned on pole 100g, thereby allowing capacitor 60 to discharge through an ammeter 110 and through the capacitor 62. Thus the circuit of FIG. 2 has been greatly simplified by the use of the relay P.

The circuit of FIG. 2 has also been improved by the addition of Zener diode voltage regulation as shown in FIG. 3. This is accomplished in circuit II by a resistor 112 and a Zener diode 113 and is provided in circuit IV by the addition of a Zener diode 114.

The alarm and warning network included in circuit III has been modified to provide both a pulsed audio or buzzer signal to indicate a significant change in the ventilation rate, and a continuous audio signal to indicate an interruption of ventilation. The continuous audible alarm is provided in substantially the same manner as in FIG. 2. If the time delay heating elements a and a of circuit I heat up because switch 34 is in one position for a prolonged period of time, one of the relay contacts 40b or 45b will be closed, thereby providing a signal through switch 27 to actuate the audible alarm 70. Also coupled in circuit III is a switch 120 which is ganged with the switch 27 to couple into the circuit a resistor 121 and a neon light 122. This network provides an indication that the audible alarm 70 is coupled into the circuit.

The pulsed audio signal portion of the circuit is actuated as a result of the position of an indicator 110a in the meter 110. The meter 110 disclosed in this alternate embodiment is preferably equipped with an optical control module 11%, shown in circuit III, and is comparable to the end of meter contacts of meter 22, shown in FIG. 2. The optical control module, in conjunction with the meter, includes photo-sensitive detectors or photocells which are responsive to the breaking of beams of light emitted from meter by the indicator 110a. The photocells and the light beams are positioned to indicate when the ventilation rate varies from an expected rate. This type of ammeter, having optical responsive indicator position means, may be purchased from Assembly Products Incorporated of Chesterland, Ohio. Upon the sensing that the ventilation rate has become either too high or too low, the control module is actuated to close relay actuated switches a and 13%. The closure of switch 130a illuminates bulb 28 and the closure of switch 1301) causes a current to flow to energize the audible alarm 70 through a normally closed relay contact 135. The contact is periodically opened due to the heating of an amperite relay control means 136 in circuit with audible alarm 70. Thus a current is periodically applied and provided to the audible alarm to sustain the pulsating buzzer.

Although the monitor device of this invention is preferably operated in conjunction with a pressure sensitive switch, it may also be used in conjunction with electrical, mechanical, hydraulic or pneumatic devices or any combination of such devices which are responsive to a change in polarity or magnitude of an electrical signal, a change in magnitude or direction of flow of a fluid or gas or responsive to some other type of periodic changing signal or force having at least two states or levels. This can be accomplished without departing from the spirit and scope of this invention, although the preferred embodiment utilizes a pressure sensitive switch so that the respirator need not be modified.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained and, since certain changes may be made in carrying out the above constructions without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

l. A respirator monitor for use with a respirator comprising in combination, means for indicating the inhalation and exhalation states of the respirator, and means in circuit with said first means for measuring the length of time said first means is in either of said states, said means for measuring including a series connection of an ampere meter and a capacitor, and a pair of normally closed relay contacts in parallel connection with said capacitor, said contacts controlled by a relay coil in circuit with said first means.

2. A monitor in accordance with claim 1, wherein said meter indicates zero time when said relay contacts are normally closed and indicates increasing time when said cpntacts are open.

3. A respiration monitoring apparatus for use with a respirator comprising, a voltage source, a relay winding in circuit with said source, a time delay relay in parallel with said relay winding, means responsive to the respirator for applying voltage from said source to said relay coil and said time delay relay, a time measuring device in circuit with said voltage source, said device comprising an ampere meter in series with a capacitor, and a pair of normally closed relay contacts in parallel with said capacitor, said relay contacts opening in response to the application of the voltage to said relay coil, and indicating means actuated by said time delay relay after said voltage has been applied to said time delay relay for a time greater than a predetermined time.

4. A respirator monitoring apparatus for use with a respirator comprising, a voltage source, means for indicating ventilation rate of the respirator including a first capacitor in circuit with said source, a parallel combination of an ammeter and a second capacitor in circuit with said source, and means responsive to a respirator for alternately connecting said first capacitor to said source and said first capacitor in parallel with said parallel combination of said meter and said second capacitor.

5. A respirator measuring apparatus according to claim 4, wherein said meter includes an indicator for indicating the number of ventilation cycles per predetermined time of a patient using the respirator.

6. A respirator measuring apparatus according to claim 5, including means for indicating when the number of ventilation cycles per predetermined time varies by a predetermined amount.

7. A respirator apparatus according to claim 6, wherein said last means includes optical sensing means responsive to the position of said indicator.

3. A respirator apparatus according to claim 6, wherein said last means includes electrical contacts responsive to the position of said indicator.

9. In a monitoring apparatus for a respirator having indicating means responsive to the operation of the respirator, the indicating means comprising first means for indicating the inhalation and exhalation states of the respirator, and second means for measuring the length of time said first means is in either of said states, the improvement characterized in that the second means includes a series connection of an ampere meter, a capacitor and switching means connected in parallel with said capacitor for permitting said capacitor to charge and discharge in response to the operation of said first means.

10. In a monitoring apparatus according to claim 9, wherein said switching means comprises relay contacts.

11. In a monitoring apparatus according to claim 10, wherein said meter indicates zero time when the relay contacts are closed and increasing time: when the contacts are open.

12. In a monitoring apparatus according to claim 9, wherein there is provided means for indicating when the respirator has been in either the inhalation or exhalation state greater than a predetermined time interval.

13. In a monitoring device according to claim 9, wherein means are provided responsive to said first means for indicating the number of ventilation cycles in a predetermined time interval.

References Cited UNITED STATES PATENTS 2,473,922 6/ 1949 Tobias 340-213 2,511,868 6/1950 Newsom 324-68 2,743,417 4/1956 Hollman 324-68 2,830,580 4/1958 Saklad et a1 128-1458 2,831,181 4/1958 Warner 340-213 2,832,335 4/1958 Huxley et al 128-302 3,106,205 10/1963 Caldwell 128-140 3,114,365 12/1963 Franz 128-1458 3,120,843 2/1964 Hyman.

FOREIGN PATENTS 745,307 2/ 1956 Great Britain.

RICHARD A. GAUDET, Primary Examiner.

K. L. HOWELL, Assistant Examiner.

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