Patent GB-1377069-A (GB)
Title: Lung ventilator
IPC: A61M16/00
Filed: 1971-12-14
Abstract: 1377069 Lung ventilators VERIFLO CORP 14 Dec 1971 [14 Dec 1970] 58053/71 Heading AST [Also in Divisions F2 and G3] A cyclically-operable pneumatically-operated lung ventillator for supplying breathing gas to a patient via a conduit 160, Fig. 1A, 1B, has a two-position master operation pneumatic switch 35 having a single means to selectively switch the ventilator between a volume-cycled and a pressure-cycled mode by a single movement from one position to another, the ventilator in the volume-cycled mode supplying a predetermined volume of gas to conduit 160 over a predetermined time during each inspiratory phase and then being automatically actuated to the expiratory phase for a predetermined time, the ventilator in the pressurecycled mode supplying the gas to conduit 160 whenever the pressure therein drops below a predetermined level and stopping the supply whenever a predetermined higher pressure is attained in the airway conduit. In the volumecycled mode, a cycle generator 50, including an inspiration time valve 100, generates control-pressure signals PC1, PC2 at outlets 94 and 85 respectively, PC1 and PC2 having the form shown in Fig. 3. The signal PC1 passes to an assembly 110 incorporating the valve 100, having a logarithmically-shaped stem 107 adjustable by knob 103 to set the inspiration time, and a valve 120 having a logarithmicallyshaped plug 130 adjustable by a knob 121 to set the volume of gas supplied per cycle, knob 103 also adjusting the valve 120, without movement of a scale indication given by knob 121, so that the volume supplied per cycle remains at the indicated valve as the inspiratory time is altered. A flow-controller 140 receives signal PC1 via conduit 161 and signal PC2 via conduit 99 and during inspiration supplies gas from supply 20 via valve 120 to conduit 160 at a flow rate proportional to (PC1-PC2), the flow rate thus decreasing during each inspiratory phase.  The generator 50, Fig. 2 (not shown) and Fig. 1A, comprises a plug (58) joined to a seat (60) and the diaphragms 52, 53 and acted on by springs (63), (69), the force exerted by spring (69) being adjustable by a knob 73 controlling the inspiratory/expiratory time ratio, a plug 83 joined to a seat (84) and to diaphragms 54, 55, chambers (66) and (82) vented to atmosphere, a conduit 49 from the regulator 23, a chamber (75) connected to a fixed bleed 80 and via a check valve 90 and conduit 101 to the valve 100 which includes a check valve 109. When seat (60) is away from an inlet (57) connected to conduit 49 the pressure therein becomes PC1 which is applied to diaphragm 52 and sent to the conduit 101. PC1 causes a flow through valve 100 to build up pressure PC2 in conduit 98 against diaphragm 53 until it reaches a value at which plug (58) moves to shut inlet (57), the pressure PC1 established in chamber 61 bleeding to atmosphere via bleed 80, and pressure PC2 move gradually decreasing as it flows back through valve 100 to PC1 conduit 101 which bleeds to the atmosphere via bleed port (86) until the plug (58) moves back to open inlet (57) to start the next cycle. In the pressure-cycled mode an airway conduit pressure sensor and controller 200, Figs. 1A and 13, senses the pressure in conduit 160 and a signal generated at and around a detector diaphragm 227 is transmitted to a relay valve 235 and sent via conduit 181 and valve 35 to the controller 140 to act as the control pressure PC1 and is also transmited to a pressure switch 320, an exhalation switch 300, and an override valve 280. During inspiration the pressure in conduit 160 increases until diaphragm assembly 202, 205 moves away from a sealing position on the end of a tube 231 so that conduit 181 is bled to atmosphere shutting off controller 140 during expiration. A new inspiration phase is initiated in the pressure-cycled mode by the patient breathing in and lowering the pressure in conduits 160, 165 and in chamber 204 so that the tube 231 is shut off again by a seat 224 to re-establish the pressure PC1. The controller and sensor 200 is operative in the volume-cycled mode to supply a signal to. an override switch 180 when the pressure in conduit 160 is below a set limit so that pressure PC2 is bled to atmosphere to initiate a new inspiratory phase. The controller and sensor 200 comprises a plug 214 connected to diaphragms 213, 215, a chamber 203 open to atmosphere via port 212, a plug 205 mounting the seat 224 and diaphragms 202, 221 and acted on by springs 206, 207 the force of spring 206 being adjusted by knob 210 to set the sensitivity of controller 200 to vacuum in conduit 160, a plug 230 carrying the tube 231 and a diaphragm 227, a chamber 222 connected via passage 223 to atmosphere, a chamber 228 connected via a restriction 229 to the regulator 23 which is also connected to a chamber 246 in a relay valve 235 having a port 250 opened and closed via poppet 248 to supply the conduit 181 with a control signal via a chamber 242 which may be vented to atmosphere via a passage 245 (closeable by poppet 248) in a plug 243 (carrying diaphragms 236, 237) a chamber 240 and port 241, and there being a pressure regulator 255 controlling the pressure supplied from the control conduit 181 via switch 35 and conduit 274 to a chamber 216 between diaphragms 213, 215, conduit 274 being connected to atmosphere via a restriction 273 and regulator 255 being adjustable by knob 257 so that the pressure in conduit 160 at which controller 200 switches from inspiration to expiration is adjustable. When the patient breathes in to initiate inspiration the pressure in chamber 204 decreases, seat 224 approaches tube 231 causing the signal in conduit 181 to increase until it overcomes the force of sprig 233 and creates a snap action, aided by movement of assembly 213, 214, 215 to engage the plug 205, that holds the tube 231 against the seat 224 thereby locking the signal in conduit 181 at its maximum value. The signal in conduit 181 starts to decrease from maximum when the pressure in conduit 160, which increases as the inspiratory phase proceeds, is sufficient to move assembly 202, 205 away from tube 231 and when the signal goes below half maximum diaphragm 227 is moved by spring 233 and tube 231 is suddenly moved further away from seat 224 and the signal in conduit 181 rapidly drops to its minimum by a snap-action and the expiration phase begins. Auxiliary devices provided include a "sigh" device comprising a chamber 172 and operative in the volume-cycled mode to increase the inspiratory time by a fixed amount (inspiratory/ expiratory ratio remaining constant) when connected to generater 50 on depressing a button 175. An override valve 280, comprising a diaphragm 286, check valve 284, and bleed valve 294, is operative to act on the controller 200 to initiate a new inspiratory phase if a given cycle has exceeded a duration of preferably about 10 seconds, unless a new inspiratory phase has already been initiated by the patient (in the pressure or volume-cycled mode) or by generator 50 (in the volume-cycled mode). An exhalation switch 300 receives the control signal PC1, derived from generator 50 or controller 200 depending on the mode of operation, from outlet 45 of valve 35 and is connected to conduit 160 via a restriction 310 and is operative during expiration to send an actuating signal via one of connectors 312 via valves 311 to low-pressure-actuated exhalation valve. The signal PC1 is also used to control a pressure switch 320 which may control a high-pressure actuated exhalation valve and which during inhalation supplies gas to the patient via connectors 321, 322 and a nebuliser and humidifier respectively, such supplied gas being taken from the conduit 127 connecting valve 120 to controller 140 so that in the volume-controlled mode, the total volume supplied remains at the setting indicated by knob 121. A manual-start switch 345 may be used to initiate a new inspiratory phase on pressing a stem 268. Excessively high or low pressures in the conduit 160 are relieved by valves 350, 360 respectively. A pressure gauge 375 is connected to conduit 160.