WO1986000537A1

WO1986000537A1 - Method and apparatus for supplying gas mixtures to an in vivo respiratory system

Info

Publication number: WO1986000537A1
Application number: PCT/US1985/001280
Authority: WO
Inventors: Leonard M. Sieracki; Gerald P. Durkan
Original assignee: Sieracki Leonard M; Durkan Gerald P
Priority date: 1984-07-09
Filing date: 1985-07-09
Publication date: 1986-01-30
Also published as: EP0188548A1; AU4634385A

Abstract

A homogenous mixture of a sedative gas and a respirating gas is supplied upon inspiratory demand to an in vivo respiratory system. The sedative gas is included in the mixture supplied to the in vivo respiratory system upon inspiratory demand essentially only if the respirating gas is simultaneously being supplied to the in vivo respiratory system. A sensor (24) detects an occurrence of negative pressure as an indication of inspiration in the in vivo respiratory system. A respirating gas supply valve (32) responsive to the sensor (24) communicates the respirating gas to the in vivo respiratory system. A second sensor detects the communication of the respirating gas to the in vivo system. A sedative gas supply valve operating in response with the second sensor allows sedative gas to be transmitted to the in vivo system along with the respirating gas in accordance with the detected supply of the respirating gas. In one embodiment the second sensor comprises a pressure to electric sensor (26) which upon detecting pressure associated with the supply of respirating gas actuates an electrically-operated sedative gas supply valve (34). In another embodiment the second sensor comprises fluidic circuitry wherein the supplied respirating gas is utilized to actuate a pneumatically-operated sedative gas supply valve (34').

Description

-i-

METHOD AND APPARATUS FOR SUPPLYING GAS MIXTURES TO AN IN VIVO RESPIRATORY SYSTEM

BACKGROUND This invention pertains to apparatus and methods for providing gas mixtures to an in vivo respiratory system.

In many situations it is desirable to supply a second gas, such as a sedation agent, to in vivo respiratory system along with the supply of a first gas or respirating gas such as oxygen. The amount of the supplied gas should generally be in controlled relation to the amount of respirating gas. For example, U.S. patent application S.N. 446,542, filed 3 December 1982 by the Applicants herein, now U.S. patent 4,462,393 discloses an embodiment wherein both respirating gas and a second gas are supplied to an in vivo respiratory system. The same circuit controls a rirst or respirating gas valve means and a second gas valve means- through which the respective gases are supplied to the in vivo respiratory system. A serious problem results if the second gas is continually applied when, for one reason or another, the respirating gas is no • longer being supplied^'. In the above regard, examples of the types of gases which can be supplied along with respirating gas to a patient to achieve a sedative effect include anesthetic gases and analgesic gases. Analgesic gases

5 are often used, for example, in a dental office for relaxing a patient prior to the performance of a dental operation. A typical prior art analgesic gas delivery system employed in such a setting includes the mixing of the- analgesic gas (such as nitrous oxide) and oxygen

10 from two distinct and independent continuous flow delivery systems. In this respect, prior art analgesic gas delivery systems comprise sources for each gas and respective associated flowmeters. The flowmeter associated with the nitrous oxide source is generally

- - adjustable through a range of from approximately 0 to approximately 8 liters per minute; the flowmeter associated with the oxygen source is generally adjustable through a range of from approximately 3 to approximately 10 liters per minute. Tubes or lines

20 leading from the respective flowmeters are typically connected to a mixing valve. The mixing valve has an output port connected to a nasal mask worn by the patient.

Gas delivery systems such as that described

25 above are generally required to supply essentially the total tidal volume of respirating gas required by the patient for each and every breath, although it is understood that some ambient air such as that entering the mouth, for example, can in some instances augment

30 the supply from the delivery system. In this respect, prior art sedative gas delivery systems operate in a continuous flow mode to provide gases to the patient throughout the respiratory cycle. The typical concentration of nitrous oxide is about 25% to 50% of

35 the total gas mixture and is a function inter alia of the patient's state of anxiety and physiological characteristics. The application of the analgesic normally starts with a supply of essentially 100% oxygen. The supply of oxygen is then gradually decreased while the supply of nitrous oxide is increased until the desired sedation effect has- taken place. Once the mask is placed on the patient, the supply of oxygen must not cease, and in any event the sedative gas should certainly not be supplied absent the essentially simultaneous supply of an appropriate volume of oxygen. If the oxygen level in the oxygen nitrous oxide mixture is insufficient, brain damage can occur.

In view of the serious problems which develop when oxygen is not being properly supplied to a patient receiving a sedating gas in a total tidal volume system, practioners must continuously monitor the condition of the patient's respiratory system and the supply of oxygen to the patient. To some extent prior art devices have endeavored to help the practioner monitor the patient and the oxygen supply. For example, many prior art sedative gas delivery system include a safety mechanism to shut off the supply of nitrous oxide, when an oxygen valve is closed. In addition, some vendors of bottled oxygen and bottled nitrous oxide have an audible alarm associated with the bottles to indicate low pressure and thus hopefully avoid the unexpected interruption of gas supply. Another device, disclosed by SCURLOCK in U.S. patent 3,952,740, alerts the practioner to a fall in oxygen pressure by activating an alarm. According to the SCURLOCK disclosure, when -an insufficient diverting flow of oxygen is present in a control stream to a fluidic OR/NOR logic gate, a gaseous anesthetic is switched by the fluidic gate to flow through the NOR outlet which is connected to activate a pressure electric switch to sound an alarm. SCURLOCK is concerned with the ratio of two gases being supplied to a patient in a continuous flow mode. When the alarm is sounded, the practioner then must take further steps to shut off the supply of the anesthetic gas.

A further concern regarding sedative gas delivery systems is that sedative gas not be wasted and that only minimal amounts of the sedative gas be leaked to the atmosphere. Sedative gases are rather expensive and their presence in the atmosphere is not desirable. Recent studies have shown increases in spontaneous abortion and congenital abnormalities in children of workers exposed to nitrous oxide. The potential risks of hepatic and renal disease, cancer, and central nervous system disorders among exposed personnel have also apparently increased.

Because of the high levels of sedative gases such as nitrous oxide that are introduced into an operating room, manufacturers have taken steps to alleviate the hazards to the attending personnel. One technique is to use a scavenger system to suck the expired gas in the vicinity of the mouth of the patient away from the operating room and exhaust it outside of the room. Unfortunately the scavenger mask generally interferes with the ability of the practioner to operate in the oral cavity due to the hinderance of extra tubing. An alternate method employed by some dental clinics and small offices is to have a large fan in the room to exhaust^' the air in the room very rapidly. These methods do not effectively reduce the supply of sedative gas since the gas is being essentially continuously supplied. Moreover, these methods waste energy in sucking out heated air in the i

-5- winterti e and cool air in the summertime, thus causing the climate control system for the operating room to work harder.

Therefore, it is an object of the present invention to provide safe and economical methods and apparatus for supplying gas mixtures including a sedative gas to an in vivo respiratory system.

An advantage of the present invention is the provision of method and apparatus for automatically terminating the supply of a sedative gas if the application of a respirating gas ceases.

A further advantage of the present invention is the provision of method and apparatus for providing a sedative gas to an in vivo respiratory system in accordance with inspiratory demand.

Yet a further advantage of the invention is the provision of a demand respirating gas supply method and apparatus which employs a single line, thereby allowing pressure sensing and gas supply to be accomplished through the same line.

SUMMARY In various embodiments of gas supply method and apparatus, a homogenous mixture of a sedative gas and a respirating gas is supplied upon inspiratory demand to an in vivo respiratory system. The sedative gas is included in the mixture supplied to the in vivo respiratory system upon inspiratory demand essentially only if the respirating gas is simultaneously being supplied to the in vivo respiratory system. In one embodiment, a sensor detects an occurrence of negative pressure as an indication of inspiration in the in vivo respiratory system. A respirating gas supply valve responsive to the sensor communicates the respirating gas to the in vivo respiratory system. A second sensor detects the

-6- communication of the respirating gas to the- in vivo system. A sedative gas supply valve operating in response with the second sensor allows sedative gas to be transmitted to the in vivo system along with the respirating gas in accordance with the detected supply of the respirating gas. In one embodiment the second sensor comprises a pressure to electric sensor which upon detecting pressure associated with the supply of respirating gas actuates an electrically- operated sedative gas supply valve. In another embodiment the second sensor comprises fluidic circuitry wherein the supplied respirating gas is utilized to actuate a pneumatically-operated sedative gas supply valve.

Various ones of the embodiments described above employ a three-way valve as the respirating gas supply valve. The three-way valve has ports connected to the first sensor, the source of the -respirating gas, and to a single line used to communicate gas to an interface.or application means worn by, attached to, or inserted in the in vivo respiratory system.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Fig. 1 is a schematic diagram showing apparatus for supplying gas mixtures according to a first embodiment of the invention;

Fig. 2 is a schematic diagram showing apparatus for supplying gas mixtures according to a second embodiment of the invention; and, -7-

Fig. 3. is a schematic diagram of a fluidic control circuit -of the embodiment of Fig. 2.

DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 shows a hybrid electrical/fluidic apparatus for supplying two gases mixed in such a manner as to supply a homogenous mixture of gases to an in vivo respiratory system. The apparatus of the embodiment of Fig. 1 comprises a source 20 of a first or respirating gas (such as oxygen); a source 22 of a second or sedative gas (such as nitrous oxide, for example); first sensor means 24; second sensor means 26; a first flowmeter 28; a second flowmeter 30; first valve means 32; second valve means 34; and, application or interface means for supplying the mixture to the in vivo respiratory system (such as a nasal mask 36).

A master switch 40 functions as a three-way contact switch for selecting whether the apparatus is to function in a continuous supply mode of operation; in a demand dose supply mode of operation; or, whether the supply of gases is to be turned off. In this respect, two further 3-way switches 42 and 44 are slaved to the master switch 40. Switch 42 is on a line 46 which is connected to the first source 20. Switch 44 is on a line 48 which is connected to the second source 22. In its "continuous" position switch 42 enables the source 20 to communicate with a line 50 during the continuous supply mode of operation. In its "dose" position switch 42 enables the source 20 to communicate with a line 52 during the demand dose supply mode of operation. Likewise, in its

"continuous" position switch 44 enables the source 22 to communicate with a line 54 during the continuous supply mode of operation, while in its "dose" position switch 44 enables the source 22 to communicate with a line 56 during a demand dose supply mode of -8- operation. In the illustrated embodiment the second gas supplied by source 22 is a sedative gas such as an ^• anesthesia or an analgesic.

The first sensor means 24 comprises a fluidic logic element such as a fluid amplifier 60 and a pressure-to-electric conversion means such as P/E switch 62. The fluid logic element 60 has an input or power port 60a; control ports 60b and 60c; and, output ports 60d and 60e. The input or power port 60a is connected to fluidic line 52 by a fluidic line 61 having a variable flow restrictor thereon. The output port 60d is connected by a fluidic line 64 to a pressure sensitive input port 62a of the P/E switch 62. An output port 62b of the P/E switch 62 is connected by electrical conductor 66 to an input terminal 68a of a control circuit 68. An output terminal 68b of the control circuit 68 is connected by electrical conductor 70 to an electrical terminal of the first valve means 32. The first valve means 32 is a two-position three-port solenoid spool valve having ports 32a, 32b, and 32c. In a first position of the valve means 32 the port 32a is communicable with port 32c. In a second position of the valve means port 32a is communicable with port 32b. Port 32a is connected to the in vivo respiratory system through fluidic line 72. Port 32b is selectively communicable through lines 52 and 46 to the source 20 of the- first gas. The port 32c is selectively communicable with the control port 60b of sensor 60 through fluidic line 74.

The continuous mode supply line 50 connects with line 72 at a point 76. Downstream from point 76 at a point 78 a fluidic ine 80 connects with fluidic line 72. The end of fluidic line 80 which is not connected to line 72 is connected to a pressure -9- sensitive input port 26a of the second sensor means such as P/E switch 26. The electrical output terminal 26b of the P/E switch 26 is connected by electrical conductor 82 to the electrical terminal of the second valve means 34.

The second valve means 34 is, in the illustrated embodiment of Fig. 1, a two-position, two- port solenoid spool valve having ports 34a and 34b. In a first position of the valve means 34 port 34a does not communicate with port 34b; in a second position the ports 3.4a and 34b do communicate. Port 34a communicates with the in vivo respiratory system through a fluidic line 84. The port 34b selectively communicates through lines 56 and 48 to the source 22 of the second or sedative gas.

The continuous mode supply line 54 connects with line 84 at a point 85. Downstream from point 85 at a point 86 a fluidic line 87 connects with fluidic line 84. The end of fluidic line 87 which is not connected to line 84 is connected to a pressure sensitive input port 88a of a P/E switch 88. The electrical output terminal of 88b of the P/E switch 88 is connected by electrical conductor 89 to an LED as hereinafter described. Fluidic lines 90 and 91 are connected to output ports 28b and 30b of flowmeters 28 and 30, respectively. Flowmeters 28 and 30 are both of a type having an orifice-type selector valve. The ends of lines 90 and 91 which are not connected to the flowmeters are connected to a "T" coupling 92 at which point the supplies of gases as governed by the respective flowmeters are mixed together. A single line 93 connects the "T" coupling 92 to the application or interface means such as the nasal mask 36. It should be understood that various types of interface or application means other than a nasal cannula are used in differing embodiments, such as a nasal cannula.

An apnea alarm circuit 95 is connected by electrical conductor 96 to an output terminal 68c of the control cirucit 68. The circuit details of both the control circuit 68 and the apnea event detection/alarm circuit 95 are basically disclosed in U.S. patent application S.N. 446,542 filed 3 December 1982 and incorporated herein by reference. In this respect, when activated P/E switch 62 of the presently described embodiment closes a switch in control circuit 68 in the manner in which switch 36 is closed in circuit 32 of the incorporated application. Also, conductor 70 of the present invention basically corresponds to line L3 of the incorporated application for controlling the solenoid valve 32. A difference between the circuit 32 shown in the incorporated application and the circuits 68 and 95 of the* present invention is the value of the 100K variable potential resistor R2 of the circuit 32 of the incorporated application. For use in the present invention the value of the resistor R2 should be set so that a dose sufficient to last at least for the duration of normal inspiration is supplied, such as a dose lasting about 1.5 seconds, for example.

The apparatus of Fig. 1 also includes a control pannel 97 having various diagnostic indicators thereon. In this regard, a. first indicator device, such as light-emitting diode (LED) 98, is connected by electrical conductors 99 and 82 to the output terminal 26b of P/E switch 26. When LED 96 is lit an indication is provided that the first gas or respiratory gas is being supplied on line 72. A second LED 100. is connected by electrical conductor 110 to an output

-11- terminal of the apnea circuit 95. LED 100 essentially corresponds to LED 94 of the incorporated application Serial Number 446,542. When lit, LED 94 provides an indication that the in vivo respiratory system has not attempted an inspiration within a predetermined interval of time from the previous inspiration. A third LED 112 is connected by electrical conductor 89 to the output terminal 88b of the P/E switch 88 as described above. When lit, the LED 112 provides an indication that ports 34a and 34b of valve means 34 are communicating with one another to thus permit the supply of the second or sedative gas on line 84. The embodiment of Fig. 2 resembles the embodiment of Fig. 1 but is a primarily fluidic rather than a hybrid electric fluidic system. In this respect, the output port 60d of the fluidic logic element 60 is connected to an input terminal 150a of a fluidic control circuit 150. The structural details of the fluidic control circuit 150 are seen hereinafter with reference to Fig. 3. A output terminal 150b of the fluidic control circuit is connected by fluidic line 152 to an input port 154a of a pilot valve 154. An output port 154b of the pilot valve 154 is connected by fluidic line 156 to the control terminal of a pressure-activated solenoid valve 32'. The port connections of fluidic valve 32' are similar to the port connection of the valve 32 of Fig. 1 as described hereinbefore, it being understood that valve 32'. is a pressure-activated solenoid spool valve while the valve 32 is an electrically-activated solenoid spool valve.

A second output terminal 154c of the pilot valve 154 is connected by a fluidic line 164 to an apnea event detection/alarm circuit 95'. The circuit 95' is not considered a part of the present invention -12- but is in one embodiment a fluidic timing circuit such as circuit 10 shown in U.S. patent 4,414,982 which is incorporated herein by reference.

Rather than having second sensor means comprising a P/E switch, the fluidic line 80 of the embodiment of Fig. 2 connects line 72 to a pressure input port 26a' of a fluidic pilot valve 26'. An output port 26b' of the pilot valve 26' is connected by fluidic line 166 to the fluidic control terminal of second valve means 34'. The second valve means 34' comprises a fluidic pressure-activated, two-stage, two- port solenoid spool valve having ports 34a' and 34b* selectively communicable in the fashion of the second valve means 34 of the embodiment of Fig. 1. The second terminal 26b' of the pilot valve 26' is also connected by a line 167 to a pressure sensitive input terminal 168a of a P/E switch 168. The output terminal 168b of the switch 168 is connected by electrical conductor 170 to the LED 96. An embodiment of the control circuit 150 of

Fig. 2 is shown in detail in Fig. 3. As described hereinbefore, the control circuit 150 has an input port 150a connected to line 64' and an output port 150b connected to line 152. The control circuit 150 comprises a fluidic one shot 180 and a substantially closed-loop fluidic path 182 having one or more timing means thereon.

The fluidic one shot element 180 of control circuit 150 has a power input 180a; control ports 180b and 180c; and, output ports 180d and 180e. Power input port 180a is ultimately connected through appropriate conventional flow restrictor devices to a fluidic source such as source 20, for example. Control port 180b is connected to input port 150a. Output port 180d is formed whereby the power stream is discharged therefrom to atmosphere when pressure is equalized at control ports 180b and 180c. Output port 180e is formed whereby the power stream is discharged to create a fluidic signal on line 152 when the pressure at control port 180b exceeds the pressure at control port 180c.

The closed-loop fluidic path 182 has a first end connected to the input port 150a and a second end connected to control port 180c of the one shot 180. The timing means shown in Fig. 3 on the fluidic path 182 comprise a fluid restrictive device 184 and a capacitance device 186. As shown in Fig. 3, the restrictor 184 is a variable resistor and the capacitance 186 is a variable capacitance, such as an elastomeric balloon. The values of the restrictive device 184 and capacitance 186 are chosen whereby the time delay for the equilization of pressures at control ports 180b and 180c is at least as great as the duration of normal inspiration such as about 1.5 seconds, for example.

In operation, an operator first manipulates the master switch 40 to select the desired mode. If a continuous supply mode is selected, switch 40 controls switches 42 and 44 whereby line 50 communicates with line 46 and line 54 communicates with line 48. If a demand dose supply mode is selected, switch 40 controls switches 42 and 44 whereby line 52 communicates with line 46 and line 56 communicates with line 48. The operation of the demand dose supply mode is discussed hereinafter under the assumption that master switch 44 is manipulated to be in the "dose" position.

. The operator then sets the flowmeters 28 and 30 to establish desired flow rates for the respective gases. In this respect, the first flowmeter 28 is adjustable through a range from approximately three to

-14- approximately ten liters per minute. In the illustrated example the first flowmeter 28 is used to control the flow of oxygen. The second flowmeter 30 is adjustable through a range of from approximately zero to approximately eight liters per minute and, in the illustrated example., is used to control the flow of a sedative gas such as nitrous oxide. The operator is then ready to install the interface or application device so that the homogenous mixture of gases. can be supplied to the in vivo respiratory system. In an illustrated example, nasal mask 36 is inserted over the nose.

When operating in the demand dose mode of operation negative pressure relative to ambient occurs in the in vivo respiratory system as an indication of respiration. Upon inspiration the first valve means 32 is in the position shown in Fig. 1 with port 32a communicating with port 32c. The negative pressure created by inspiration is transmitted through the first valve means 32 and on fluidic line 74 to the control port 60b of the first sensor means 24. The negative pressure applied to control port 60b causes an output signal normally discharged through output port 60e to shift to output port 60d. The fluidic signal at output port 60d is applied on fluidic line 64 to the pressure sensitive input port 62a of P/E switch 62. The application of fluidic pressure at input port 62a of P/E switch 62 results in the generation of an electrical signal on conductor 66 for application to the control circuit 68.

As understood with reference to the incorporated application, the control circuit 68 uses the electrical signal on conductor 66 to generate an electrical signal on conductor 70 for actuating the • electrical solenoid valve means 32. . Actuation of the

-15- valve means 32 by the application of a signal on conductor 70 causes the spool valve to slide to a position whereat port 32a is connected to port 32b. When ports 32a and 32b of valve means 32 are so connected, the first gas is supplied from the source 20 along lines 46 and 52, through the valve 32, along line 72, through flowmeter 28, and along lines 90 and 93 for application to the in vivo respiratory system. As described above, the control circuit 68 actuates valve means 32 to supply gas from source 20 for a duration at least as long as the duration of normal inspiration.

The second sensor means 26 senses the supply of the first gas on line 72. In this respect, supply of the first gas on line 72 also creates a pressure on line 80 which activates the pressure sensitive input port 26a of the P/E switch 26. Pressure at the input port 26a of switch 26 causes the P/E switch 26 to generate an electrical signal at its output port 26b. The electrical signal at output port 26b is transmitted on electrical conductor 82 to the electrical terminal of the electrical solenoid spool valve 34. The application of electrical signal at the electrical terminal of the valve 34 actuates the valve 34 whereby valve 34 moves to a position where port 34a communicates with port 34b. When ports 34a and 34b are so connected, the second gas supplied from source 22 along lines 48 and 56, through the valve means 34, along line 84, through flowmeter 30, and along lines 91 and 93 for application -to the in vivo respiratory system. In this respect, at point 92 the first and second gases are mixed together so than a homogenous - mixture is applied on line 93 to the in vivo respiratory system. The supply of the second gas on

-16- line 84 is detected by P/E switch 88, which generates an electrical signal on conductor 89 to illuminate LED 112.

The operation of Fig. 2 basically resembles the operation of Fig. 1. It should be understood,

^'however, that the fluidic output signal for port 60d is applied to the input port 150a of the fluidic control circuit 150. An output signal is generated by control circuit 150 on line 152 for a time duration determined by the timing means on the closed-loop path 182 of circuit 150.. As described above, the values of the timing means 184 and 186 on path 182 are so chosen whereby the time delay before pressures equilize at control ports 180b and 180c is at least as great as the duration of normal inspiration. At the end of the time delay, circuit 150 ceases generation of the output signal on line 152.

The output signal of the fluidic control circuit 150 is applied on fluidic line 152 to the input terminal 154a of the pilot valve 154. When the pilot valve 154 is activated, a fluidic signal at the output port 154d causes the solenoid spool valve 32' to move to the position whereat port 32a' is connected to port 32b' , thereby causing the first gas to be supplied to the in vivo respiratory system in substantially the aforedescribed manner. The pressure on line 72 created by the supply of first gas is incident upon the input port 26a' of pilot valve 26', causing the pilot valve 26' to generate a fluidic output signal on line 166. The signal on line 166 actuates the solenoid valve 34' whereby port 34a' is connected to port 34b' for permitting the second gas to be supplied and mixed homogeneously in substantially the aforedescribed manner. When master switch 44^' is manipulated to be in the "continuous" position the first gas from source 20 is continually supplied on lines 46, 50, 72, and 90 from source 22 and the second from source 22 on lines 48, 54, and 91 to point 92 whereat the first and second gases are homogeneously mixed for continuous application on line 93 and via mask 36 to the in vivo respiratory system.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will- be understood by those skilled in the art that various alterations in form and detail may be made therein without departing from the spirit and scope of the invention. For example, the P/E switch 26 and valve 34 of Fig. 1 are in another embodiment replaced with a pilot valve and a fluidically-actuated solenoid valve.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for supplying two gases mixed in such a manner as to supply a homogenous mixture to an in vivo respiratory system, said apparatus comprising: a source of a first gas; a source of a second gas; interface means for applying said first and second gases to said in vivo respiratory system; first sensor means for determining an occurrence of negative pressure relative to ambient in said in vivo respiratory system; means for connecting said first sensor means to said interface means; first valve means responsive to first sensor means for communicating said first gas to said in vivo respiratory system through said interface means; second sensor means for determining when said first gas is being communicated to said in vivo respiratory system; means for connecting said supply of second gas to said in vivo respiratory system; and, second valve means responsive to said second sensor means for communicating, said second gas to said in vivo respiratory system essentially only when said ' -first gas is being communicated to said in vivo respiratory system.

2. The apparatus of claim 1, wherein said first valve means has first, second, and third ports, said^' first port being selectively communicable with either said second port or said third port, and wherein said means for connecting said first sensor means to said

-19- interface means comprises a single line connected to said first port of said valve means, said line adapted both to transmit to said first valve means negative pressure indicative of an inspiration in said in vivo respiratory system and to transmit at least said first gas to said in vivo respiratory system.

3. The apparatus of claim 2, wherein said single line connecting said interface means to said first valve means has connected at an intermediate point thereon a further line which connects said single line to said second valve means.

4. The apparatus of claim 1, further comprising: means for controlling said first valve means, said control means being responsive to said first sensing means for selectively connecting said first port of said first valve means to said second port thereof when negative pressure is sensed and for maintaining said connection for at least a portion of the time duration of said negative pressure in said in vivo respiratory system so that said first gas may be supplied to said in vivo respiratory system, said control means also being adapted to reconnect said first port to said first valve means to said third port thereof after the- application of said first gas to said in vivo respiratory system.

5. The apparatus of claim 1 wherein said first sensor means comprises a fluidic element having a power stream input port, a control port, and two output ports, said power stream input port being connected to said. source of said first gas, said control port being communicable with said in vivo respiratory system, and a first of said output ports being connected to means for

-20- controlling said first valve means whereby an occurrence of negative pressure relative to ambient at said control port generates a fluidic signal at said first output port, said fluidic signal at said first output port being utilized by said first valve control means for operating said first valve whereby said first gas is communicated to said in vivo respiratory system.

6. The apparatus of claim 5, wherein said first sensor means further comprises pressure to electric signal conversion means, and wherein said first output for of said fluidic element is connected to said pressure to electric signal conversion means.

7. The apparatus of claim 1, wherein said second sensor means comprises pressure to electric sensor means.

8. The apparatus of claim 1, wherein second sensor means comprises a fluidic pilot valve.

9. The apparatus of claim 1, wherein said second gas is a sedation agent.

10. The apparatus of claim 9, wherein said second gas is an anesthetic.

11. The apparatus of claim 9, wherein said second gas is an analgesic.

12. The apparatus of claim 11,- wherein said second gas is nitrous oxide.

-21-

13. A method of supplying two gases mixed in such a manner to supply a homogenous mixture to an in vivo respiratory system, said method comprising the steps of: using first sensor means for determining an occurrence of negative pressure relative to ambient in said in vivo respiratory system; operating first valve means in response to said first sensor means for communicating a first gas to said in vivo respiratory system; using second sensor means to sense the communication of said first gas to said in vivo respiratory system; and, operating second valve means in response to said second sensor means for communicating a second gas to said in vivo respiratory system.

14. The method of claim 13, further comprising the step of: using a single line to connect said first valve means to interface means for applying said first gas to said in vivo respiratory system, said first valve means having first, second, and third ports, said first port being selectively communicable with either said second port or said third port; said single line being connected to said first port; of said first valve means, said line adapted both to transmit to said first valve means negative pressure indicative of an inspiration in said in vivo respiratory system and to transmit at least said first gas to said in vivo respiratory system.

15. The method of claim 14, further comprising the step of:

-22- controlling said first valve means in response to said first sensing means for selectively connecting said first port of said first valve means to said second port thereof when negative pressure is sensed and for maintaining said connection for at least a portion of the time duration of said negative pressure in said in vivo respiratory system so that said first gas may be supplied to said in vivo respiratory system, said control means also being adapted to reconnect said first port of said first valve means to said third port thereof after the application of said first gas to said in vivo respiratory system.

16. The method of claim 13, wherein said second gas is a sedation agent.

17. The method of claim 16, wherein said second gas is an anesthetic.

18. The method of claim 16, wherein said second gas is an analgesic. _. ...

19. The method of claim 18, wherein said second gas is nitrous oxide.