Patent GB-1408242-A (GB)
Title: Respirator
IPC: A61M16/00
Filed: 1973-04-25
Abstract: 1408242 Respirator systems SUTTER HOSPITALS MEDICAL RESEARCH FOUNDATION 25 April 1973 [1 May 1972] 19535/73 Heading A5T A volume-cycled respirator comprises gas delivery means displaceable for forcing a volume of gas under pressure into the lungs of a patient during an inspiratory period of a respiratory cycle, drive means for displacing the gas delivery means, means for generating a reference signal representing a time-varying position of the gas delivery means during the cycle necessary to deliver a desired volume of gas in accordance with a desired volume-versustime wave-form, and closed loop feed back means for continuously controlling changes in the position of the gas delivery means whereby gas is delivered in accordance with the desired waveform, the feed back means including first means responsive to the actual position of the gas delivery means for generating a position feedback signal representing the actual volume of gas delivered and second means responsive to the reference signal and position feedback signal for providing a position error signal which is applied to the drive means to control the position of the gas delivery means throughout the inspiratory period.' The apparatus may comprise a piston and cylinders 32, 34 supplying gas to a patient through line 42 under the control of a computer and waveform generator 46 programmed to give an output signal 54 proportional to the desired volume of gas to be delivered as a function of time, the signal 54 being adjustable manually or automatically by an input 58 representing an optimum waveform generated by the computer. The position of piston 32 is continuously adjusted to maintain desired gas flow by a transducer 74 which determines the instantaneous position of piston 32 within cylinder 34 and produces a signal 76 proportional to the volume of gas delivered to the patient. The signals 54, 76 are compared at summing point 78 to produce an end signal 80 representing deviation from the desired volume, this signal 80 being fed to the piston drive means 36 to continuously adjust the position of the piston. Adjustable respiratory rate, inspiration-expiration time ratio and tidal volume commands are delivered to the computer. The piston is preferably actuated electrically. A secondary piston and cylinder 98, 96 may be provided for storage of gas which cannot be accepted by the patient, the gas accommodated therein being forced into the patient's lungs at the end of the inspiratory cycle. An analogue computer 100 receives signals 104, 108 from transducers 102, 106 respectively proportional to the pressure in cylinder 34 (and the patient's lungs) and the position of piston 98. The computer 100 produces an output 112 representing a desired waveform for time dependent pressure build-up in the patient's lungs and this signal is compared at summing point 128 with actual pressure build-up waveform 126 derived from a logic circuit 118 computing time elapsed in the inspiratory cycle and pressure signal 104. The pressure end signal 130 is converted to a position end signal 132 partially controlling the position of piston 98. Computer 100 is also programmed to actuate piston 98 so that the entire predetermined volume of gas is fed to the patient by the end of the inspiratory cycle. To avoid excessive pressure build-up in the patient's lungs if the volume of gas within cylinder 96 is high towards the end of the inspiratory cycle means are provided for prolonging the cycle. A pressure relief valve 148 is also provided to vent excess pressure to atmosphere. Means for introducing an artificial sigh into the respiratory cycle may be provided.