GB1312799A - Lung ventilators - Google Patents

Abstract

1312799 Lung ventilators BRITISH OXYGEN CO Ltd 20 Jan 1972 [20 Oct 1970] 49847/70 Heading A5T A lung ventilator includes a timer 40 adapted to be put in a condition to switch the lung ventilator from an expiratory mode to an inspiratory mode before the expiratory gas flowrate has dropped to a chosen level, the operation of the timer being inhibited until signals from an expiratory flow sensor 26 indicate that the expiratory flow-rate has reached the chosen level. The ventilator includes' a mixer 2, a pattern generator 4, a flow control device 6, and a valve 8 which is biased open during the inspiratory phase and which is controlled by a control device 10. An input sensor 12 produces an electrical pulse each time a unit volume of gas passes through the sensor and the train of pulses is transmitted to an integrator 14. An analyser 18 checks the efficiency of the mixer 2, and beyond the analyser the gas is supplied to the patient through an airway 20. Expiratory gas passes along an exhaust line 22 and through a sensor 26 which transmits pulses to a second integrator 27 and to a gate 48. Gas leaving the sensor 26 passes through a valve 28 which is controlled by the gas pressure in a control line 30 bled off from the airway 20. A comparator 36 receives a signal from the integrator 14 and from a preset standard volume signal-generator 38, and when the measured volume of gas passing through the sensor 12 is equal to the preset volume set by the generator 38 the control device 10 is actuated to close valves 8 and 34 to switch the ventilator to the expiratory mode. Closure of the valve 34 also triggers the timer 40 via a pressure switch 39 to transmit a signal resetting the comparator 36 when a chosen time interval has elapsed. Triggering of the timer 40 causes a constant input voltage to be applied through a resistor to a capacitor forming part of the timer. The gate 48 which is located in the line connecting the timer 40 and the comparator 36 prevents transmission of the resetting signal until the pulse train from the sensor 26 indicates that the chosen expiratory flow-rate has been achieved. The integrator 27 is connected to an alarm 44 which is actuated when the patient ceases to breathe or the supply of gas falls excessively.