GB1287564A - Automatic lung ventilators - Google Patents

Abstract

1287564 Lung ventilator VICKERS Ltd 15 Oct 1969 [15 July 1968] 33717/68 Heading AST [Also in Division G3] An automatic lung ventilator comprising an expiratory valve 70 for connection in the breathing gas supply line to the patient, a bistable fluidic switching element 4 connected to control the valve and hence the patient's expiration and a fluidic oscillator comprising bistable fluidic switching elements 1, 2 and 3 connected to element 4 for causing it to alternate between its two stable states so that valve 70 is open when element 4 is in one state, and closed for the other state. Element 4 comprises a fluid input 41, control jets 42, 46, 43, 47 and two outlets 44 and 45, an output through one outlet representing one stable state. Fluidic capacitors 29, 39 comprising cylinders with pistons are provided to control the frequencies of the oscillations. In an embodiment, larger bistables 5 and 6 are provided to amplify fluid flow to the patient or a "diaphragm activated pneumatic power booster" may be used. An element 7 is provided to open and close valve 70. Elements 8 and 9 provide feedback from the patient to elements 1 and 4 as shown. In use, the ventilator normally oscillates between an inspiratory phase with valve 70 closed and an expiratory phase with the valve open at fifteen c.p.s. The output of element 8 is normally biased, by capacitor 60, through outlet 85. If the patient improves during the expiratory phase, the pressure at jet 82 is reduced and the output of element 8 is taken through outlet 84, thus causing elements 1 and 4 to switch states and hence switch the ventilator to the inspiratory phase. Sensitivity is controlled by valve 89 and capacitor 88. The output of element 9 is normally through outlet 94 during the inspiratory phase. If excess lung pressure arises, determined by valve 90, the output switches to outlet 93 thus switching elements I and 4 and switching the ventilator to the expiratory phase. In an embodiment, a five element oscillator including two elements with only two control valves is disclosed (Fig. 2, not shown). In an embodiment (Fig. 3, not shown) an oscillator directly controls an on/off valve connected to a gas supply by a line having a "T" piece to deliver gas to the patient.