US 3669108 A
Description (OCR text may contain errors)
I United States Patent 1151 3,669,108 Sundblom et al. 1 1 June 13, 1972  VENTILATOR Primary Examiner-Charles F. Rosenbaum Assistant ExaminerJ. B. Mitchell  Inventors: Leif J. Sundblom, Castro Valley; Louis A.
OHM", Menlo Park both of Calif. Attorney-Owen, W1ckersham & Erlckson  Assignee: Veriflo Corporation, Richmond, Calif. ABSTRACT  Filed; O t, 20, 1969 A ventilator capable of both pressure-cycled and volume-cyled ti A al 1 1 PP 861,804 Zd053552afi'conifiiihelifiil'liiiiiii ififiiinii'i sigifii conduit reaches a first predetermined pressure level and 52 us. 01. ..l28/l45.8 128/1422 Closes Off the downstream nduit from the gas supply conduit is 1 1 1m. c1. .A62b 7/02 when Press"re the comma signal conduit drops belw  Field of Search ..12s/145.s, 1455-1451, sewnd predetermined Pressure "Piramry 128/! 4 145 cle, the command signal conduit and the downstream conduit are bled to atmospheric. The inspiratory cycle may be in-  References Cited itiated (l) by the patient breathing in and thereby lowering airway pressure, or (2) after a time lapse following the com- UNITED STATES TENTS mencement of said expiratory phase, the duration of said time lapse being determined as a set multiple of the time of the 3,265,061 8/1966 Gage ..l28/ 145.8 preceding inspiratory phase. The expiratory phase may be 3,114,365 12/1963 Franz itiated (l) by the achievement of a redetermined airwa 1 s 145 s p y 3 3 7/ 1967 Bird at 2 pressure or (2) upon the delivery of a predetermined volume 3,504,670 4/1970 l-loel ...l28/l45.8 ofgas 3,434,471 3/1969 Liston ..l28/l45.8
45 Claims, 18 Drawing Figures PRESSURE 0 1 VOLUME CYCLE o INIT- 62o RAT'O INSPIRATORY PRES-S SGHS TIME 285 VOLUME 1760' SmH MAN AL 3010 Ai lT 328% 113 k 'PATE'NTEDJun13I912 I 1 3.669108 sum o1nF12 LV-I FIG'IC INVENTORS LEIF J. SUNDBLOM LOUIS A. OLLIVIER a/Mbzw ATTORNFYS PAIENTEDJuu 13 m2 sum 02 or 12 GAS FIG/I8 FIGJC INVENTORS SUNDBLOM ATTORNEYS PATENTEDJuu 13 I972 sum on or 12 @IRMY PRESSURE 62a NEGRATlO TIME VOLUME PRES'S. SIGHS )4 176d"@ 285 237a I INIT MH 328 1 I Fl 6. 3
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sum 12UF12 INVENTORS LEIF J. SUNDBLOM BY LOUIS A. OLLIVIER 00m, ll/ulmlh i ATTORNEYS VENTILATOR This invention relates to an improved ventilator capable of both pressure-cycled and volume-cycled operation. Can be either Pressure-cycled or Volume-cycled Ventilators heretofore on the market have either been pressure-cycled or volume-cycled and have not been capable of shifting from one form of operation to the other, as is the device of the present invention, where simple movement of a selector handle accomplishes the shift. Hence, prior-art ventilators were strictly limited to one of these two types of operation and extra machines were required. The present invention enables a single machine to become very versatile and to be adapted to the needs of the patient and to the desires of the doctor. Moreover, as will be seen, the ventilator of this invention also gives greater versatility within each type of operation than has been available from prior-art machines.
F low Pattern Adjustable Another difficulty with the ventilators heretofore on the market has been that their flow pattern of delivery has been capable of little, if any, adjustment; each has had a basically fixed flow pattern. It is desirable to have a large initial flow at the beginning of the inspiratory phase and to have the flow gradually diminish toward a predetermined minimum flow at the end of the inspiratory phase.
The ventilator of the present invention enables a wide range of adjustment of the flow pattern, and any such flow pattern is reproducible independently of the time setting of the cycle. The maximum initial flow can be adjusted to a desired amount, the smaller terminal flow at the end can be adjusted to what is desired, and the change from one to the other adjusted too.
Automatic Ratio of Inspiratory Time to Expiratory Time The ventilator of this invention also provides for setting a ratio between the inspiratory time and either the maximum or the actual expiratory time in the breathing cycle. This adjustment, once set, is maintained until purposely reset, but a wide range of such ratios is readily obtainable. Thus, this ratio setting enables full control of the patients breathing cycle on the basis that the longer it takes to inhale, the longer it takes to exhale, and each inspiration controls the succeeding expiration, and a new inspiratory phase is initiated at the right time. This same ratio setting can be used as a backup expedient when a patient normally initiates each inspiratory phase himself but if he fails to do so within a time bearing the set ratio to his previous inspiration, the machine will itself begin the new inspiratory phase.
Independent Setting of inspiratory Time and Tidal Volume In its volume-cycled mode the ventilator of this invention is also capable of a separate noninteracting adjustment of the total volume and the inspiratory time, so that either the time or the volume can be changed without changing the other, whereas heretofore adjustment of one would require adjustment of the other, each time a change is made. In this invention there is a novel interaction of parts that automatically cares for these adjustments.
Pressure Sensitivity and Safety When the device is used in its pressure-cycled mode, the airway pressure is employed to sense a patients initiation of a new inspiratory phase and then to feed the breathing gas to him at a doctor-set rate and manner. In addition, the airway pressure is used to terminate the inspiratory phase and commence an expiratory phase. Furthermore, in both the pressure-cycled and volume-cycled modes of operation, patient safety is assured by a pressure-activated safety release that terminates the inspiratory phase before a dangerous airway pressure is reached. Manual Override In both volume-cycled and pressure-cycled operation the doctor can readily override and initiate a new inspiratory phase manually simply by pressing a button provided for that purpose.
Supply Pressure and Gas Mixture Versatility A significant object of the invention is to provide a ventilator that can be used with relatively low pressures, such as 25 psig supply pressure, instead of requiring a supply at 50 psig, or higher.
Many optional features are also available in this ventilator, such as a change from pure oxygen to air-diluted oxygen, the use of so-called negative pressure" where that is desirable and the elimination of it where it is not, and the adjustment of many other factors.
The ventilator of this invention is supplied with a compressed gas such as oxygen, air or a premix of air and oxygen at a regulated pressure, typically of approximately 50 psi, though that may be varied. When using oxygen as the supply gas the ventilator of this invention will deliver pure oxygen or an oxygen-air mixture in the pressure-cycled" mode. In the volume-cycled mode, the ventilator will deliver pure oxygen only. When using air as the supply gas, the ventilator will deliver air in both the pressure-cycled and volume-cycled modes. When using mixture obtainable from an oxygen ratio controller, the ventilator will deliver the same oxygen-air mixture as that supplied in either pressure-cycled or volume-cycled modes.
In normal breathing, from time to time a person will take an exceptionally deep breath and then exhale that deep breath. This sigh is quite useful in maintaining healthy conditions. Most breathing machines make no provision for other than consistent uniformity. The device of the present invention makes it possible for the doctor to cause a sigh at suitable intervals, super-imposing the sigh on the regular cycle without upsetting subsequent regular cycling until the next sigh.
Other objects and advantages of the invention will appear from the following description of a preferred form of the invention.
In the drawings:
FIGS. 1A, 1B, and 1C comprise a pneumatic circuit diagram of a ventilator embodying the principles of the present invention. The three views fit together and comprise a single diagram.
FIG. 2 is a view in perspective of the exterior of a ventilator unit embodying the principles of the invention.
FIG. 3 is a view on an enlarged scale and in front elevation of a preferred embodiment of the main control valve from the circuit of FIG. 18, being a component of the unit of FIG. 2.
FIG. 4 is a view in rear elevation of the valve of FIG. 3.
FIG. 5 is a view section taken along the line 5-5 in FIGS. 3 and 4.
FIG. 6 is a view in elevation and in section, on an enlarged scale, of a preferred embodiment of the initiator or sensitivity control valve used in the circuit of FIG. 18.
FIG. 7 is a view in elevation and in section, on an enlarged scale, of a preferred embodiment of the pressure controller of the circuit of FIG. 1B.
FIG. 8 is a view in elevation and in section, on an enlarged scale, of a preferred embodiment of the volume profile regulator of FIG. 1A.
FIG. 9 is a top view, partly broken away and shown in section, on an enlarged scale, of a preferred embodiment of the volume control unit of FIG. 1A.
FIG. 10 is a view in section taken along the line 10-10 in FIG. 9.
FIG. 11 is a view in section taken along the line 11-11 in FIG. 10.
FIGS. 12A, 12B, 12C, and 12D are diagrammatic views showing the operation of the compensator port with respect to the volume port at extreme settings of the volume and inspiratory time control shafts, all for the unit of FIGS. 9 to 11.
FIG. 13 is a view in section taken along the line 13-13 in FIGS. 9 and 10.
THE SELECTOR VALVE ASSEMBLY 12 (FIG. 1B)
In FIG. 1B a supply 10 of oxygen at some desired pressure is provided. The supply 10 may include a regulator or other device to provide the desired pressure, and the oxygen supplied may be pure oxygen or air or a mixture of oxygen and air. For that matter, other gases may be used if desired. The supply 10 is connected by a conduit 11 to a manually operated valve assembly 12 at an inlet 13. The valve assembly is operated by a valve control lever or selector 12a shown in FIG. 2.
The valve assembly 12 is preferably provided with five valves, each of which has three positions, an 011" position, a pressure-cycled" position, and a volume-cycled" position. Thus, the assembly 12 includes a valve 14 connected to the inlet 13, which either shuts off the supply of oxygen from the conduit 11 or, in the volume-cycled mode, sends it to a volume-cycled outlet 15 or, in a pressure-cycled mode, sends it to a pressure-cycled" outlet 16. The outlets l and 16 are connected to a main internal supply conduit 20. Since the outlets 15 and 16 are connected together, the valve 14 acts substantially as an off-on" valve, either passing the full supply of oxygen or cutting it off completely, but the structure shown is preferred in order to provide a simple ganged assembly 12, that is, the valve 14 is ganged with valves 17, 18, 19, and 29 for movement of all of them together between these three positions; either all of valves 14, 17, 18, 19, and 29 are in off position, or all of them are in the pressure-cycled" position, or all of them are in the volume-cycled" position.
The second valve 17 of the valve assembly 12 has an inlet 21 which is always connected to the main conduit 20 and which is connected alternately to a volume-cycled outlet 22 or a pressure-cycled outlet 23 or is blocked in an off position. Like the first valve 14, the second valve 17 is operative in both the pressure-cycled and volume-cycled modes.
The third valve 18 of the valve assembly 12 has an inlet 24 which is either connected to a pressure-cycled" outlet 25 or is blocked off in both its off position and its volumecycled position. In other words, the valve 18 is operative only in the pressure-cycled mode.
The fourth valve 19 of the valve assembly 12 has an inlet 26, a volume-cycled" outlet 27 and a "pressure-cycled outlet 28, and the fourth valve is operative in both the pressure-cycled and volume-cycled modes.
The fifth valve 29 of the valve assembly 12 has an inlet 85 connected in the volume-cycled mode alone to an outlet 86 that leads directly to the atmosphere. There are no inlets in the of position or the pressure-cycled mode; so the fifth valve 29 is operative only in the volume-cycled mode.
It is stressed that all of the valves in the assembly 12 are linked together for simultaneous operation, so that all of them are either off, are in the volume-cycled" position, or in the pressure-cycled position. It has been noted that the valves 14, 17, and 19 are operative in both modes, the valve 19 operative only in the pressure-cycled mode and the valve 29 operative only in the volume-cycled.
THE MAIN VALVE 30 (FIGS. 1B and 3-5) The internal supply conduit 20 leads to a main valve 30 at a normally closed inlet 31; when a closure member 32 is retracted from an opening 33, oxygen from the conduit 20 can pass via an outlet 34 to a downstream conduit 35.
The closure member 32 is secured to two diaphragms 36 and 37, which cooperate with the housing assembly 38 to divide the interior of the main valve 30 into three chambers 39, 40, and 41. The housing 38 (FIG. 5) is so constructed that the diaphragm 36 has a significantly smaller area exposed to the gas than does the diaphragm 37. The chamber 39 lies between the smaller area diaphragm 36 and the inlet 31 and outlet 34; this chamber 39 is used for the passage of the supply gas. In between the two diaphragms 36 and 37, the chamber 40 is provided with a port 42 that communicates with a command signal conduit 43. The third chamber 41 is kept at atmospheric pressure by an atmospheric bleed port 44 and contains a spring 45 which urges the diaphragms 36 and 37 and the clo' sure member 32 toward the closed position. As shown in FIGS. 3 to 5, bolts 46 may be used both to hold the housing assembly 38 together and to mount the valve 30 to a support member 47, shown in phantom lines.
The spring 45 acts to keep the closure member 32 against the inlet port 31 until the pressure in the chamber 40 and the command signal conduit 43 rises above a predetermined value (e.g., 18 psig), well above atmospheric pressure. Then, the fact that the pressure in the chamber 40 acts on a larger area on the diaphragm 37 than on the diaphragm 36, causes the diaphragm 37 to move toward the chamber 41 and thereby move the closure member 32 away from the inlet 31. As soon as the high-pressure gas from the conduit 20 begins entering the inlet 31 and flowing into the chamber 39, it acts on the diaphragm 36, and thus both the diaphragm 36 and 37 are then causing the closure member 32 to open. The result is that once the critical pressure in the chamber 40 and command signal conduit 43 is reached, the main valve 30 opens the inlet very quickly in what is, in effect, a snap action. The inlet 3] then sends gas from the main conduit 20 into the downstream conduit 35.
In order for the closure member 32 to close off the inlet 31, the pressure in the chamber 40 and in the command signal conduit 43 must drop to a predetermined level well below the pressure that opens the inlet 31, e.g., 9 psig. As will be seen the conduit 43 is bled to atmosphere, and when the pressure level does fall below this second, lower, critical level, the closure member 32 does close the inlet 31. Subsequently, as will be seen, the pressure in the downstream conduit is bled toward atmospheric.
THE DOWNSTREAM CONDUIT 35 (FIGS. 1A and 1B) The downstream conduit 35 communicates directly with the valve 19 at its inlet 26. The effects of this connection, which accomplish one of the main functions of the downstream conduit 35, are explained later. The downstream conduit 35 also communicates directly, as by branch conduits, with a check valve 48 and a first pressure relief valve 50, both to be described later. Further, as shown in FIG. 1A, the conduit 35 communicates with a second pressure relief valve 51, the function of which is also explained later. Still further, the conduit 35 communicates by an inlet 53 with a chamber 54in a negative-pressure" control valve 55; the internal supply conduit 20 also communicates with the negative pressure control valve 55 through an inlet port 56 leading into a chamber 57 on the opposite side of a diaphragm 58 from the chamber 54. This valve, too, is dealt with further below. Finally, the downstream conduit 35 also communicates with a sigh device 300 (FIG. 1C).
THE AUTOMATIC RATIO EXPIRATORY TIMER (FIG. 1B)
The command signal conduit 43 and the internal supply conduit 20 are connected to an automatic ratio expiratory timer 60. The purpose of this device is to conclude the expiratory phase of operation quite positively and to initiate a new inspiratory phase, in the event the patient does not do so himself by actuating the initiator discussed in the next section. In other words, the expiratory phase is either terminated in every cycle by this timer 60 or at least it is always there to set a maximum time limit for the expiratory phase. This time, moreover, is not a time constant, since it takes longer to exhale after a long-drawn breath than to exhale a shorter-drawn breath. Hence, the timer determines the maximum length of each expiratory phase as a set ratio to the length of the immediately preceding inspiratory phase. The set ratio is, itself, set by the physician and can be changed at his order.
The automatic ratio expiratory timer 60 (FIG. 18) comprises a principal valve 61, the check valve 48, the relief valve 50 and a needle valve 62, regulated by the control 62a in FIG. 2.
The valve 61 has three chambers 63, 64, and 65 provided by two diaphragms 66 and 67, the diaphragm 67 having a much larger exposed area than the diaphragm 66 (compare the valve 30). The first chamber 63 is connected by an inlet 68 to the main inlet conduit 20. The two diaphragms 66 and 67 are both rigidly connected to a closure member 70, which a spring 69 normally urges to close a port 71. When the port 71 is opened, it connects the chamber 63 to the command signal conduit 43. The smaller area diaphragm 66 which closes the chamber 63 cooperates with the larger area diaphragm 67 to provide the central chamber 64, which is bled to atmosphere at all times through a port 72. On the opposite side of the large diaphragm 67, is the chamber 65 which has two ports 73 and 74. The port 73 is connected to the check valve 48 through a restricted orifice 75.
The port 74 is connected to an inlet 76 of the pressure relief valve 50, on the opposite side of a diaphragm 77 from a port 78 that is connected to the downstream conduit 35. The diaphragm 77 and a spring 79 normally keep the inlet 76 open,
except when the pressure at the port 78 is large enough to overcome the pressure of the spring 79 and the pressure on the other side of the diaphragm 77 in the chamber 80. The diaphragm 77 divides the valve 50 into chambers 80 and 81, and a bleed line 82 leads by a port 83 in the chamber 80 to an adjustable needle valve 62, which is used to set the ratio in the timing operation, as will be described subsequently.
During inspiration, gas from the downstream conduit 35 flows through the check valve 48, and the restricted orifice 75 into the chamber 65 and builds up pressure there, for the inlet 76 is then shut off by the full pressure of the downstream conduit 35 acting through the inlet 78 on the diaphragm 77. The orifice 75 is small, but as pressure builds up and becomes great enough, it closes the closure member 70 against the port 71 and disconnects the command signal conduit 43 from the main gas supply conduit 20.
When the inspiratory phase ends and expiration begins, the downstream conduit 35 and the command signal conduit 43 are back bled to the atmosphere (how will be explained below), and then the inlet 76 is opened and the chamber 65 is bled slowly to atmosphere at a controlled rate through the needle valve 62. Backflow from the chamber 65 to the downstream conduit is prevented by the check valve 48. Depending on the amount of gas in the chamber 65 which depends on the duration of the inspiratory phase the time for the chamber 65 to drop to a predetermined pressure will vary. At that pressure, the closure member 70 is opened, and gas flows via the chamber 63 from the main gas supply conduit into the command signal conduit 43. The command signal conduit 43 then raises the pressure in the chamber 40 of the main valve 30 and opens the inlet 31 to start a new inspiratory phase.
While different values can be used, the springs may be set to close off the port 71 when the pressure in the chamber 65 is about 7 psig. The orifice 75 may be set so that in the maximum time for inspiration, the pressure in the chamber 65 will reach about 35 psig.
THE INITIATOR OR SENSITIVITY CONTROL 90 (FIGS. 1B and 6) The command signal conduit 43 is also connected by a branch to an initiator or sensitivity control device 90. This initiator 90 is used in the pressure-cycled mode to initiate the inspiratory phase, by overriding the automatic ratio expiratory timer 60, which thus performs a backup function. The patients own termination of his expiratory phase is used to trigger the passing of gas from the main gas supply conduit 20 into the command signal conduit 43, thereby actuating the main valve 30. The initiator 90 may also be used in the volume-cycled mode, if desired, though normally it is not so used. In fact, if desired the volume port 22 of the valve 17 may simply be shut off.
The initiator 90 has three chambers 91, 92, and 93 provided by a housing 94, a diaphragm 95, and a rigid partition 96, as shown in a preferred embodiment in FIG. 6. The chamber 92 between the diaphragm 95 and the rigid partition 96 is kept at atmospheric pressure by an atmospheric bleed port 97. The chamber 93 between the rigid partition 96 and the housing 94 is provided with an inlet 98 that is connected to or disconnected from a port 104 by a closure member 100 which is connected to and is actuated by the diaphragm 95. An adjustable spring 101 exerts pressure on the diaphragm 95, urging the closure member 100 toward a position disconnecting the inlet 98 from the port 104. This inlet port 98 is connected by a conduit 102 and the pressure port 23 of the valve 17 to the main gas supply conduit 20. It may also, through an on-off valve 103, be connected to the volume port 22 of the valve 17, so that the volume-cycled mode may or may not use the sensitivity control device 90, whereas the pressure-cycled mode always uses this device 90. The command signal conduit 43 is connected to the chamber 93 by a port 104. There is also a very important port 105 for the chamber 91, discussed in the next section.
In the preferred structure shown in FIG. 6, the diaphragm 95 has a bracket 99 secured thereto in engagement with a rod or shaft 106. An O-ring 109 provides both a seal where the rod 106 passes through the partition 96 and a pivot for it to swing about. The closure member 100 comprises a disc threaded adjustably to the shaft 106 and provided with an annular gasket 108, effective in all rotational positions of the disc to close the outlet port 104 except when the diaphragm 95 causes the rod 106 to tilt and pivot on the O-ring 107. The spring 101 is of the leaf type with a right-angle portion 109 attached to the rod 106, in a way to enable some relative movement, such as sliding. A screw 87 enables adjustment of the spring pressure, thereby setting the pressure requested for the diaphragm 95 to open or close the port 104. There is a stop 88 for the shaft 106 and a set-screw 89 for the disc-valve 100. The spring 101 can be adjusted to set the patient-actuated pressure over the range between about 1 centimeter of water and 15 centimeters of water.
THE FACE MASK 110 AND THE AIRWAY CONDUIT 113 (FIGS. 1A and 1B) The patient typically wears a face mask 110 (FIG. 1A), which is connected by a conduit 111 to an exhalation valve 112. From the exhalation valve 112, a conduit 113 at airway pressure is connected (FIG. IE) to the sensitivity control device 90 at the port 105 on the opposite side of the diaphragm 95 from the central chamber 92 and on the same side as the spring 101. When the pressure in the airway 113 drops, the diaphragm 95 is moved by the pressure of the spring 101, to tilt the rod 106 and open the port 104, as will be seen subsequently in the explanation of the operation of the ventilator.
THE PRESSURE SAFETY VALVE (FIG. 1B)
The airway conduit 113 is also connected to an inlet 119 of a pressure 5 safety valve 120 leading in between two diaphragms 121 and 122 that divide the valve 120 into chambers 123, 124, and 125. The idea here is to prevent the buildup of any dangerous pressure in the lungs. The effective area of the diaphragm 121 is larger than that of the diaphragm 122. On the opposite side of the larger diaphragm 121 is a spring 126, and (like the structure of the main valve 30) the smaller diaphragm 122 and the larger diaphragm 121 are both connected to a valve closure member 127 which closes an inlet 128 that is connected to the command signal conduit 43. When the port 128 is open the command signal can flow to atmospheric pressure through the chamber 125 a bleed port 129. The chamber 123 is also bled to atmospheric pressure. If the pressure in the airway 113 becomes excessive (i.e., rises above a predetermined pressure, such as 70 centimeters water, set as a limit by the spring 126), it acts on the diaphragm 121, overcomes the pressure of the spring 126 and opens the inlet 128, bleeding the command signal conduit 43 to atmosphere and thereby terminating the inspiratory phase.
THE PRESSURE CONTROLLER 130 (FIG. 18 AND 7) Normally, however, the inspiratory phase in the pressurecycled mode is terminated by a pressure controller 130. If the sigh function is to be omitted, the pressure controller may be built just like the pressure safety valve 120, but set for lighter pressure to provide the normal pressure control for the ventilator. When the sigh function (see below, re FIG. 1C) is incorporated, a preferred embodiment of the pressure controller 130 may be as shown in FIG. 7. This unit 130 has a diaphragm 131 of larger effective area than either diaphragm 132 or diaphragm 133, between which it lies, and these diaphragms 131, 132, and 133 cooperate with a housing 114 to provide chambers 115, 116, 117, and 118, a spring 134 being in the atmospheric chamber 118. The diaphragms 131 and 132 and 133 are secured together and to a closure member 135 and normally urge it against an inlet port l36,which joins the end chamber 115 to the command signal conduit 43. When the closure member 135 is moved away from the port 136, the command signal conduit 43 is bled to atmosphere through a port 137. The chamber 117 between the two diaphragms 131 and 133 has a port 140 connected by a conduit 141 to the pressure outlet 25 from the valve 18, and thereby, to the airway 113. The spring 134 is adjusted by a handle or shaft 142 to give a desired pressure on the closure member 135. A guide pin 143 engages a groove 143a in a nut 143b to guide the nut 143b without rotation when the shaft 142 is turned. Since the valve 18 has its inlet 24 connected to the airway pressure conduit 113, when and only when the valve assembly 12 is in the pressure-cycled mode, the airway pressure is then conducted to the central chamber 116 of the pressure controller 130. The chamber 117, which lies between the diaphagms 131 and 133 is connected by a port 138 to a conduit 139 leading to the sigh device 300.
Omitting for the present the effect of the sigh apparatus 300, the main function of the pressure controller 130 is to terminate the inspiratory phase when the pressure in the airway 113 reaches a predetermined pressure. At this pressure, since the pressure in the airway 113 is also the pressure in the line 141 and in the chamber 116 during the pressure-cycled mode, the pressure in the chamber 116 and the pressure of the spring 134 are overbalanced, and the command signal line is bled to atmospheric pressure through the inlet 136, chamber 115, and port 137. The command signal conduit 43 bleeds away the pressure in the chamber 40 of the main valve 30, and the port 31 is therefore closed. The operating point of the pressure controller can be set over a range of about to 50 cm water.
THE AIR SWITCH 145 AND PROFILE FLOW CONTROLLER 150 (FIG. 1A)
In the pressure-cycled mode, the valve 19 is used to connect the downstream pressure conduit 35 leading from the main valve 30 to a conduit 144 leading to an air switch 145 (FIGS. 1A and 2). The air switch 145 is a manually operated valve which sends the oxygen from the conduit 144 through a flowrate controller 150 to provide a controlled flow of the pure oxygen or sends it through a venturi 149, at which air is picked up to dilute the oxygen. It determines whether the patient gets 100 percent oxygen (if that is the gas supplied at the supply or one of various dilutions thereof.
Thus, the air switch 145 in one position connects the conduit 144 to a conduit 146 leading to a variable needle valve 147 and thereby through a restrictor orifice 148 to the venturi 149, and thence to the airway conduit 113 to send oxygen-enriched air to the mask 110 therethrough.
In its other position, the air switch 145 connects the conduit 144 to a conduit 151 which leads to the profile flow controller 150, comprising a valve unit 152 with three chambers 153, 154, and 155. Two of the chambers 153 and 154 are divided from each other by a diaphragm 156 with a spring 157 in the chamber 153. The chamber 153 is kept at atmospheric pres sure through a bleed port 158. The third chamber 155 is divided from the central chamber 154 by a poppet valve 160 and opening 161. The poppet valve 160 is normally urged into the opening 161 to close it by a spring 162 and is also actuated by the diaphragm 156. An inlet conduit 163 into the third chamber is connected to the conduit 151 by a conduit 159 and conducts oxygen into the central chamber 154 when the poppet valve is open, at a rate determined by the amount by which the poppet valve 160 is open. The gas may then pass through an outlet pon 164 and from thence to the airway pressure conduit 113. A by-pass is provided through a conduit 165 and a needle valve 166 to give a much smaller flow rate of gas from the conduit 151 to an inlet port 167 into the central chamber 154. This is the terminal or minimum flow.
A pressure relief valve 168 may be incorporated to bleed the airway 113 to atmosphere if the pressure introduced from the port 154 should become excessive.
The pressure flow controller 150 sends gas to the patient at a regulatable large initial amount and at a flow rate that gradually reduces toward or to a set minimum rate. The pattern of reduction, the rate at which the flow rate decreases, is determined by the pressure on the spring 157, which is adjustable to the patients requirements or to the prescribed treatment. The maximum or initial flow rate is set by the spring 157, and the minimum or terminal flow is set by the needle valve 166. Typically, the terminal flow is adjustable in the range of l to 10 liters per minute, and the peak flow is adjustable in the range of 60 to 100 liters per minute.
THE NEBULIZER 170 (FIG. 1A)
Preferably, the downstream conduit 35 is also connected to a nebulizer 170 (FIG. 1A) through a restricted valve 171 to give a small flow of high-pressure gas to atomize the liquid added to the main flow into the airway pressure conduit 113. Also, a pressure gauge 172 (FIGS. 1A and 2) may be connected to the airway pressure conduit 113 to give a reading of airway pressure.
THE NEGATIVE PRESSURE DEVICE AND THE EXHALATION VALVE 112(FIG.1A),
WITH ITS ASSOCIATED PRESSURE RELIEF VALVE 200 (FIG, 1B)
The negative pressure device 55, when used, connects the chamber 57 by a port 174 to a conduit 175 through an adjustable needle valve 176 (with control 176a in FIG. 2) and into the exhalation valve 112 at an inlet 177. A closure member 178 in the negative pressure device 55 is connected to the diaphragm 58, and the diaphragm 58 and a spring 179 normally keep the port 174 closed.
The negative pressure port 177 of the valve 112 leads into a venturi 180 in a chamber 181, into which the conduit 111 and 113 also open through ports 182 and 183; the flow from the venturi 180 passes to an outlet valve 184, the outlet port 185 of which is normally kept closed by the pressure of a spring 186 (or similar device, such as a bladder) on interconnected diaphragms 187 and 188, and by the pressure from a conduit 190. This conduit 190 is connected by a restrictor orifice 191(FIG. 113) to the airway pressure conduit 113. The conduit 190 is a small-diameter line so that it is very responsive, and the action will be described later. This line 190 and its restrictor conduit 191 are connected by an inlet 192 into a chamber 194 ofthe valve 112.
The line 190 is also connected to a pressure relief valve 200 at an inlet 201 (FIG. 1B). The pressure relief valve 200 has a single diaphragm 202 dividing the valve 200 into a chamber 203 having a port 204 to atmosphere on one side, and a chamber 205 having a port 206 connected to the downstream conduit 35. A spring 207 aids the diaphragm 202 in keeping the port 201 open, and when it is open, the auxiliary line 190 is bled to atmosphere.
THE PRESSURE RELIEF VALVE 51 (FIG. 1A)
The conduit 43 also leads to the pressure relief valve 51 (FIG. 1A), which is a secondary valve for the main valve 30 and is used in both modes. The valve 51 has a single diaphragm 195 with a chamber 196 on one side connected by a port 197 to the command signal conduit 43. A valve 198 connected to the diaphragm 195 is in the other chamber 199 and normally acts to close an inlet port 207a connected to the downstream conduit 35. A bleed port 208 to atmosphere is provided from the chamber 199, and a spring 209 tends to help open the valve 198.
The pressure relief valve 51 is closed so long as there is a predetermined amount of pressure in the command signal conduit 43; otherwise it is open. When the valve 51 is closed, the pressure in the downstream conduit 35 is monitored; when the valve 51 is opened, the downstream conduit 35 is bled to atmospheric. Thus, when the command signal conduit 43 has enough pressure to open the main valve 30, the same pressure closes the relief valve 51. And when the command signal conduit 43 is bled to atmosphere through either the pressure controller 130 or through the pressure safety valve 120, at the end of the inspiratory phase, the valve 51 is opened and the downstream conduit 35 is at once bled to the atmosphere.
THE MANUAL TRIGGER VALVE 210 (FIG. 1B)
For manual operation in both modes there is provided a manual trigger valve 210 (FIG. 18) comprising a valve body 211 having an inlet 212 connected to the internal supply conduit 20 and having a valve 213 normally urged by a spring 214 to a closed position at a port 215. When the valve 213 is opened by depressing a manual stem 219, the air can flow from the conduit 20 through the trigger valve 210 from the chamber 216 to the other chamber 217 and thence by a port 218 to the command signal conduit 43, whence it flows to the chamber 40 and opens the valve 40. Thus the valve 210 ena bles the physician manually to monitor the ventilator, to initiate the inspiratory phase.
All of the parts so far described are used in the pressure-cycled mode of operation, and some of them are also used in the volume-cycled mode of operation. The ones next to be described are used only in the volume-cycled mode.
VOLUME MODE: VOLUME PROFILE REGULATOR 22 (FIGS. 1A AND 8) i As stated, in the volume-cycled mode of operation the sensitivity control 90 may or may not be used, depending on whether the valve 103 is open or closed. In either event, however, the valve 19 (FIG. 1B) is set so'that the downstream gas flows from the conduit 35 into a conduit 220 leading by two branch conduits 221 and 222 to a volume profile regulator 225 and an inspiratory time regulator 240.
The volume profile regulator 225 is used to enable the flow to the patient in this mode to start at a large initial flow and then to decrease as the inspiratory phase continues until the end of the cycle. In this respect it resembles but is difi'erent from the pressure flow controller 150.
The volume profile regulator 225 (see especially FIG. 8) comprises a housing 226 having a larger area diaphragm 227, a smaller-area diaphragm 228, and a rigid partition 229. One side of the diaphragm 227 is open to the atmosphere, as by a port 2260 in the housing 226. A poppet valve 230 is urged by the diaphragms 227 and 228 and springs 231 and 231a toward a position away from an opening 232 which the poppet valve 230 sometimes closes. Gas from the conduit 221 enters by an inlet port 224 into a chamber 233 and goes through the opening 232 controlled by the poppet valve 230 to a chamber 234, and from thence by an outlet 235 to a conduit 236 leading to a control valve 237 and thence to the airway pressure conduit 113. The control valve 237 with indicator 237a in FIG. 2, enables adjustment of the volume in a manner subsequently to be explained. The control valve 237 is an integral part of a timevolume control unit 275 which is given more attention below.
The volume profile flow regulator 225 also has a chamber 238 between the diaphragm 227 and 228 with a port 239. As will be seen, during the inspiratory phase, pressure builds up in the chamber 238 and gradually reduces the flow out through the port 235 by moving the poppet valve 230 toward the opening 232. The pressures of the springs 231 and 231a, the stiffness of the diaphragms 227 and 228, and their areas relative to each other, cooperate with the variable pressure of gas into the chamber 238 to determine the profile of the inspiratory phase.
THE INSPIRATORY TIMER 250 AND ASSOCIATED ELEMENTS (FIGS. 1A)
The oxygen from the conduit 222 enters the inspiratory time regulator 240 through a flow-reducing restricted orifice 241 and an inlet port 242. The purpose of the inspiratory time regulator is to provide a supply of gas at a regulated pressure to the inspiratory timer 250. A diaphragm 243 is loaded by a spring 242 to close off a vent port 248 to atmosphere. The gas entering the inlet port 242 flows to an outlet port 245 via an annular chamber 249, except for gas that is vented to atmosphere from the chamber 249 by the vent port 248. This venting serves to keep the gas supplied to the outlet port 246 at a constant pressure, for as the pressure increases in the chamber 249, the diaphragm 243 is moved up to increase the bleed flow through the vent port 248; since a small motion of the diaphragm 243 will create a large change in bleed flow, the pressure will remain practically constant.
The regulator 240 is set to deliver to the outlet port 245 and a conduit 246 regulated pressure at a desired level, and the conduit 246 is connected through a needle valve 247 to an inspiratory timer 250, with indicator 250a of FIG. 2. The needle valves 247 and 237 are interacting and form part of the timevolume control device 275 discussed below, by which the inspiratory volume and time can be changed.
The outlet from the needle valve 247 leads to a port 251 in a fixed-capacity center chamber 252 of the inspiratory timer 250 between two diaphragms 253 and 254, a larger diaphragm 253 and a smaller diaphragm 254. To both diaphragms 253 and 254 is connected the stem 255 of a closure valve 256 for an inlet 257 which is connected to the command signal conduit 43 and normally holds that inlet 257 closed. From the chamber 258 with the inlet 257 is a bleed 259 to atmosphere, and the spring chamber 260 of the larger diaphragm 253 also has a bleed port 261 to atmosphere, as well as a spring 262 bearing on the diaphragm 253.
Thus, the gas that passes through the pressure regulator 240 and the control valve 247 gradually builds up pressure in the timer 260 during the inspiratory phase, starting from atmospheric pressure at the beginning of each inspiratory phase. When a predetermined time has elapsed, the pressure in the chamber 252 reaches a predetermined level that opens the closure member 256, uncovering the inlet port 257. As this inlet port 257 is uncovered, the rush of pressure of the gas flowing in from the command signal conduit 43 helps to snap open the valve, and the command signal conduit 43 is quickly bled to atmosphere, ending the inspiratory phase by resulting in closure of the main valve 30.
In order to prepare the inspiratory timer 250 for the next phase, by bleeding the pressure in the chamber 252 to atmospheric, the inspiratory timer 250 is connected by conduits 263 and 264 to another pressure relief valve 265 at an inlet 266. The pressure relief valve 265 has a single diaphragm 267 with a spring 268 in one chamber 269, urging a valve closure member 270 normally to open the inlet 266. The chamber 269 is bled to atmosphere by a port 271 so that when the valve 270 is in open position, the gas from the conduit 263 is vented to the atmosphere. A chamber 272 on the other side of the diaphragm 267 is connected by a port 273 to the downstream air conduit 35.
Thus, when the inspiratory timer ends the inspiratory cycle by bleeding the command signal conduit 43 to atmosphere, the drop in pressure in the conduit 43 opens the valve 51 and the downstream conduit 35 is bled to atmosphere. The resultant reduction in pressure of the conduit 35 enables the spring 268 to open the closure member 270 away from the inlet port 266, and the conduit 263 and the chamber 252 are bled to atmosphere. The valve 256 is then closed by the spring 262. When the next inspiratory phase begins, the surge of pressure in the downstream conduit 35 closes the valve 265, and the flow of gas through the needle valve 247 can build up pressure in the chamber 252.
The diaphragms 253 and 254 and the bias spring 262 are sized so that the valve seat 256 is closed when the pressure in the intermediate chamber 252 is atmospheric and opens when the pressure reaches a nominal value of 5 psig (at the end of the inspiratory phase), the pressure being created by the flow of supply gas through the needle valve 247 into the fixed capacity chamber 252. The time that it takes to build up the pressure, say, of 5 psi, represents the inspiratory time. It may be adjusted from 0.5 to 4 seconds by setting the needle valve opening 247. At the end of the inspiratory phase, the pressure is returned to atmospheric by the action of the pressure release valve 265.
The pressure increase from to 5 psig is proportional to the total volume which passes through the needle valve 247. This volume is proportional to area .r time. The total volume being a constant in the calibration, the valve opening is therefore proportional to the reciprocal of time; hence, the non-linearity of the time scale graduation.
The inspiratory timer 250 is also connected by the conduit 263 and the port 239 to the chamber 238 of the volume profile regulator 225 which lies in between the two diaphragms 227 and 228. Thus, during the inspiratory phase, the pressure builds up there and gradually moves the poppet valve 230 closer to its opening 232, shaping the fiow profile of the inspiratory phase.
As the pressure in the chamber 238 increases, it creates a force opposing the force of the spring 231, and the regulator setting is decreased. As a result, the output pressure of the regulator decreases progressively as the pressure in the chamber 238 increases. Typically, the output pressure goes from 30 psig to 5 psig as the inspiratory timer pressure goes from O to 5 psig.
THE VOLUME-TIME CONTROLLER 275 (FIGS. 1A and 9-13) A housing 276 is provided with an inlet 277 and an outlet port 278. A variable area opening is created by moving a slot 280 (preferably rectangular in cross section) of an adjustable sleeve 281 relative to a slot 283 in the stationary housing 276, the slot 283 also being preferably rectangular in cross section. A maximum size of opening is obtained when the two openings 280 and 283 coincide (FIG. 12C). Reduction from that maximum condition is done in two modes: a rotation and an axial displacement ofthe adjustable sleeve 281.
The rotation of the sleeve 281 is directly related to the volume setting (V); the axial displacement is proportional to the reciprocal of inspiratory time (Hi). The net area of the opening in then proportional to: Volume (l/Time). Since the flowrate is directly proportional to the area, we have:
Flowrate Volume x l/time) or the fundamental relationship:
Volume Flowrate x time.
The settings of volume and inspiratory time are thus independent and noninteracting. A change in volume setting modifies the opening area, and therefore the flowrate, in a direct relationship. A change in the inspiratory time setting modifies the opening area in an inverse ratio; an increase in time decreases the flowrate, in order to maintain the same total volume in a longer time.
The axial movement of the sleeve 281 is the axial displacement of a screw 284 actuated directly, by an inspiratory time knob 285, the sleeve 281 being spring loaded by a spring 286 against the screw 284 to assure cooperation between the screw 284 and the sleeve 28]. The knob 285 drives, through a step-up gear train 287, 288 the needle valve 247 of the inspiratory timer. The rotation of the sleeve 28] is obtained by a gear train 290, 291, in which the driven gear segment 291 is attached to the sleeve shaft 292 (FIG. 10), and the driving gear 290 is actuated by a volume knob 237 a (FIGS. 2 and 10).
FIGS. 12A through 12D show four extreme positions of the two orifices 280 and 283:
FIG. 12A shows the small overlap in area of the rectangular orifices 280 and 283 when the time shaft is in its full clockwise position to give the maximum time interval, while the volume shaft is in its full counterclockwise position to give minimum volume. The orifices 280 and 283 are in different planes and at minimum overlap in both directions. FIG. 128 shows the larger overlap, with both orifices on the same plane but at extreme opposite angles. This setting gives both minimum time and minimum volume, for both the time shaft and the volume shaft are in their full counterclockwise positions.
In FIG. 12C, the maximum volume is obtained, with the orifices 280 and 283 coinciding, while the time is again at minimum. The time shaft is fully counterclockwise, while the volume shaft is fully clockwise.
In FIG. 12D the volume shaft is again fully clockwise to give maximum volume, while maximum time is also obtained by having the time shaft fully clockwise.
In a typical instance, the area of the full overlapi.e., the area of each of the orifices 280 and 283, is 0.01 square inch (FIG. 12C). In FIGS. 12B and 12D, the area of overlap is then 0.001 square inch, and in FIG. 12A the area of the overlap is only 0.0001 square inch.
INTERRELATIONSI-IIPS AND GENERAL FUNCTIONING OF THE ASSEMBLY (FIGS. 1A AND 13) Now that the elements other than the sigh device 300 have been described and their individual operation indicated, some general relationships and functioning will be noted before the detailed operation is given.
As noted earlier, the selector valve assembly 12 has three positions: pressure-cycled, volume-cycled" and off." In the off position, the regulated gas supply 10 is shut off from the entire device. In the pressure-cycled position, (1) The internal supply conduit 20 to the main valve 30 is connected to the regulated gas supply 10, (2) The downstream conduit 35 leading from the main valve 30 is connected to the air switch 145. (3) The connecting line 141 between the patient supply line or airway conduit 113 and the pressure controller 130 is open. (4) The supply line 102 between the internal supply conduit 20 and the initiator is open. In the volumecycled position, (1) The internal supply conduit 20 to the main valve 30 is connected to the regulated gas supply 10, and (2) The downstream conduit 35 leading from the main valve 30 to the volume control unit 275 is open.
The two-position main valve 30 is either fully open or fully closed, depending on the command signal from the conduit 43. If the command signal, i.e., the pressure in the conduit 43 increases beyond a predetermined value, such as 20 psig, the main valve 30 opens and remains open. If the signal decreases to a lower predetermined value (such as approximately 10 psig), the main valve 30 closes.
The relief valve 51 exhausts the downstream pressure in the conduit 35 to atmosphere when the main valve 30 closes.
On a command signal from the airway conduit 113, typically a slight vacuum, the initiator 90 sends high-pressure gas from the conduits 20 and 102 to the command signal conduit 43, causing the main valve 30 to open. The reader will recall that the initiator 90 has a diaphragm that is subjected to a differential pressure; atmospheric pressure on one side in the chamber 92 and, at this time, a slight vacuum on the other side in the chamber 91 generated by the patient and sent there by the airway conduit 113. The effort created by the differential pressure opens the valve closure in the compartment 93, and the port 104 then supplies the high-pressure gas from the conduit 102 to the command signal conduit 43. The magnitude of the vacuum required to generate the control signal is adjustable by the loading spring 101.
The pressure controller 130 also senses the pressure in the airway conduit 1 13, with a desired set pressure, and when the two become equal, generates a signal to shut off the main valve 30, by bleeding the command signal conduit 43 to atmosphere.
The airway pressure, which is the patients breathing pressure, starts at atmospheric pressure or at a slight vacuum at the beginning of each inspiration,then gradually increases during the inspiratory period to the preset value; this may be a value from a minimum of 5 cm. water to a maximum about 60 cm. water. When the pressure in the airway conduit 113 has reached the preset value, the gas in the command signal conduit is exhausted to atmosphere, causing a pressure drop, which, in turn causes the main valve 30 to close, shutting off the gas supply to the patient.
The pressure safety valve 120 also senses the airway pressure, compares it with a preset maximum (approximately 70 cm. water) pressure. If the pressure in the airway conduit 113 exceeds the preset maximum pressure, a signal is generated to shut off the main valve 30, by exhausting the command signal conduit 43 to atmosphere. Again, this pressure drop causes the main valve 30 to close.
When a desired expiratory time has elapsed, the expiratory timer 60 initiates a new inspiratory phase by connecting the high-pressure gas supply conduit to the command signal conduit 43, which opens the main valve 30. During the inspiratory phase, the expiratory timer 60 is recharged. The intensity or pressure of the recharge is directly proportional to the inspiratory time. At the end of the inspiratory phase and the beginning of the expiratory phase, the expiratory timer 60 starts discharging (bleeding off air pressure) at a preset rate. When the discharge reaches a reference low level, a new inspiratory phase is initiated. If the rate of discharge is set at a value such that the discharge time is twice as long as the recharge time, the respirator is known to operate on a l:2 inspiratory/expiratory ratio. This ratio is maintained even though the inspiratory time varies from one breath to another. The automatic ratio expiratory timer 60 is effective in both pressure-cycled and volume-cycled modes.
The air switch 145 is connected to the downstream side of the main valve 30 by the conduits 35 and 144. If is effective in the pressure-cycled mode only, when it provides a selection of delivering pure oxygen through the profile flow controller 150 or an oxygen-air mixture through the venturi 149.
The flow controller 150 provides the patient with a suitable flow pattern during the inspiratory period. The demand of gas is greatest at the start of the inspiratory phase; then it gradually diminishes. The flow controller operates on the basis of creating a variable orifice 160, 161 as a function of the difference between a spring-set pressure and the patients airway pressure. The flow is then determined by the area of the orifice. By adjusting manually the magnitude of the differential pressure, a higher or lower flow rate can be obtained. A manual setting limits the maximum opening of the variable orifice 160, 161. The initial high flow, corresponding to this maximum opening, constitutes the peak flow, and the manual setting is the flow rate control. An adjustable by-pass flow through the valve 166 provides a terminal flow control.
ln the alternate position of the selector switch 145, the profile function is by-passed, and the gas supply is applied to the nozzle of the venturi 149. The flow from the nozzle draws in air, producing an air-gas mixture. The flow rate is then controlled by the needle valve 147, which is actuated by the control knob of the profile flow controller 150, thus providing a single common control knob for both operations.
The manual trigger 210 enables manual initiation of the ventilator into an inspiratory phase by connecting the gas supply conduit 20 to the command signal conduit 43, thus causing the main valve 30 to open.
A slight vacuum created at the exhalation valve 112 by the ventilator during the expiratory phase known as "negative pressure," (see U. S. Pats. Nos. 3,191,596 and 3,265,06l The driving gas supplied from the gas supply conduit 20 upstream of the main valve 30 passes through the pneumatically controlled valve 55 and then through the adjustable needle valve 176 to the venturi 180 located in the exhalation valve 112. The control valve 55 is actuated by the pressure from the downstream side of the main valve 30 by the conduit 35. The needle valve 176 enables adjustment of the value of the negative pressure.
The volume control is obtained by the volume selector 275, the inspiratory timer 250, and the volume profile regulator 225.
The volume selector 275 enables selection of a desired volume to be delivered, by setting a dial. The dial may be graduated in volume units or have reference marks. The input of the unit is connected to the downstream conduit 236 from the volume profile regulator 225. The output of the unit is connected to the patients breathing circuit.
The inspiratory timer 250 controls the time that it takes to deliver the selected volume. The supply pressure for the timer 250 is regulated to an intermediate value (e.g., approximately 25 psig) to minimize the effect of pressure variations in the main supply line 20. The gas is then metered through a needle valve 247 into the fixed-capacity chamber 252, where the pressure increases as a function of time. When the pressure reaches a reference value (e.g., 5 psig), the timer 250 exhausts the command signal conduit 43 to atmosphere which, in turn, shuts off the main valve 30 and the gas supply to the patient. Its dial may be graduated in seconds or have other reference marks.
The actions of the volume selector 275 and the inspiratory timer 250 are combined in such a way that the settings of the volume and the inspiratory time are noninteracting. Changing the volume setting does not affect the time setting; similarly, changing the inspiratory time does not affect the volume settmg.
The volume profile regulator 225 supplies the gas to the volume selector 275. It regulates the gas pressure to a maximum of, e.g., 30 psig, at the beginning of the inspiratory period and gradually reduces it to a minimum of, e.g., 5 psig at the end of the period. As a direct result of the variable pressure, the flow rate is reduced accordingly, providing a controlled pattern.
The decrease in the regulated pressure is synchronized with the control pressure of the inspiratory timer 250. This provides a reproducible flow pattern independently of the inspiratory time setting.
The pressure release valve 51 is open to atmosphere when the pressure in the command signal conduit 43 is low (near atmospheric). During the inspiratory phase, this pressure is high, and it closes the port 207a. At the end of the inspiratory phase and the start of the expiratory phase, the pressure in the conduit 43 is bled to atmospheric, causing the pressure release valve 51 to open and bleed the downstream conduit 35 to atmosphere.
The exhalation valve 1 12 provides the means of opening the patients airway to atmosphere during the expiratory period, and conversely of closing the communication with atmosphere during the inspiratory period. A plastic bladder or diaphragm 187 works in cooperation with the exhalation port to control the opening. When the bladder is inflated, (or the diaphragm 187 is under pressure) there is no communication with atmosphere. When it is deflated, the communication is established. The operation of the bladder or diaphragm 187 is automatically controlled by the ventilator through the auxiliary line 190.
OPERATION: PRESSURE-CYCLED MODE The pressure-cycle mode of operation will be described first in its use as an assist type of ventilator, with the patient supply-