Patent GB-834152-A (GB)
Title: Improvements in or relating to lung ventilator apparatus
IPC: A61M16/00
Filed: 1958-01-28
Abstract: 834,152. Respiratory appliances. AIRSHIELDS Inc. Jan. 28, 1958 [Jan. 29, 1957], No. 2786/58. Class 81 (2). Artificial respiration or anaesthetic apparatus comprises a closed chamber 12 housing a flexible container 18 connected in the respiratory circuit and means for imparting to the closed chamber a pneumatic pressure cycle which is controlled by a timing and control device 37 comprising a main valve assembly 50, 51, 52, 54, 55, 56, a control chamber 66 constantly supplied with gas through a calibrated metering orifice 64 and a second valve 75, 76 which exhausts the control chamber to atmosphere when the pressure therein exceeds a predetermined maximum so that the main valve assembly can move to one position, the second valve closing when pressure in the control chamber reaches a predetermined minimum so that pressure on the main valve assembly is maintained and holds it in a second position. The flexible bag 18 is connected by pipes 20, 26 in the respiratory circuit of an anaesthetic apparatus and is contained in a container 12, the gas pressure in which is cyclically varied so that respiratory gas in the bag 18 is alternately forced into and withdrawn from the patient's lungs. The container 12, which preferably has transparent glass or synthetic plastic walls, is connected to a bellows 30 operable by a piston 33 reciprocated within a cylinder 32. The container 12 has maximum and minimum pressure relief valves 28, 29. The piston 33 is raised, to compress the bellows 30 and thus increase the pressure in the container 12, when gas is supplied to the cylinder 32 through a supply tube 36. On the exhaust of gas from the cylinder 32 through the tube 36, the piston falls as the bellows 30 expands due to the weight of a plate 31 forming the base of the bellows 30. Gas is supplied to and exhausted from the cylinder 32 under the control of the tuning and control device 37, the inlet 47 (Fig. 2) of which is connected to a gas bottle 38 through a tube 39 and a pressure regulator 40. Gas entering the inlet 47 passes through a calibrated orifice 64 to a control chamber 66 and a second chamber 62 which is disposed above a first pair of spaced diaphragms 54, 57 interconnected by a central member 55. The pressure in the control chamber 66 gradually rises, a variable orifice controlled by an adjustable needle valve 68 being interposed between the calibrated orifice 64 and the control chamber 66. Increased pressure in the second chamber 62 depresses spaced diaphragms 54, 57 so that the central member 55 opens a main ball valve 50, 51 to permit gas to flow from the inlet 47 to the supply tube 36 and thence to the cylinder 33. On attaining a predetermined maximum, the control chamber pressure raises a second pair of spaced interconnected diaphragms 70, 73 to raise a second ball valve 75 from its seat 76 against an adjustable spring 77, thus connecting the control chamber 66 and the second chamber 62 to atmosphere through a passage 82. Reduction of pressure in the second chamber 62 allows the first pair of spaced diaphragms 54, 57 to rise so that the main ball valve 50, 51 closes, a rigid plate 58 carried by the upper diaphragm 57 disengaging a shoulder formed in the wall of a chamber 59 between the diaphragms 54, 57 so that the chamber 59 is connected with a vent 61. The supply tube 36 is thus cut off from the inlet 47 by the main valve 50, 51 but communicates with atmosphere through an aperture in the central member 55, the chamber 59 and the vent 61. The fall in pressure in the control chamber 66 is gradual, gas passing through the needle valve 68 to atmosphere. When the pressure in the control chamber 66 reaches a predetermined minimum, the spring 77 closes the second ball valve 75, 76, thus cutting off the chambers 66, 62 from atmosphere. The pressure in these chambers 66, 62 again rises and the cycle is repeated. The duration of each cycle is determined by the setting of the needle valve 68 and the relative durations of the negative and positive phases of the cycle are determined by the setting of the spring 77. A manually-operable bag 18a may be connected in the respiratory circuit instead of the bag 18.