Patent GB-827546-A (GB)
Title: Lung ventilating apparatus
IPC: A61M16/00
Filed: 1956-10-30
Abstract: 827,546. Artificial respiration apparatus. AIR-SHIELDS Inc. Oct. 30, 1956 [Nov. 7, 1955], No. 33083/56. Class 81 (2). Artificial respiration apparatus, in which the inhalation and exhalation phases differ in duration and energy requirements, includes a cylinder and piston comprising one variable volume chamber which is operatively connected to a second variable volume chamber having a movable wall (e.g. a bellows), a first channel connecting one variable volume chainber to a fixed volume chamber during part of the stroke of the piston and a second channel with a check valve through which the fixed volume chamber may be connected to atmosphere. A breathing bag 15 of a respiratory circuit is housed in a chamber 11, the pressure in which is varied cyclically by alternate compression and expansion of a bellows 12. The bellows 12 are actuated by a piston-rod 17 connected to a piston 18 in a cylinder 19. The piston-rod 17 has a slot 34 and is supported in the top of the cylinder 19 by a tube 23, a space 25 between the piston-rod 17 and the tube 23 being closed by spaced seals 24. The top 22 of the cylinder 19 has a passage 31 connecting the space 25 with the atmosphere through a ball-check valve 32 and with the interior of the cylinder 19 through a flap valve 33. A bore 28 having an adjustable valve 26 connects the interior of the cylinder 19 with the atmosphere. On supplying air to the cylinder 19 through a pipe 20, the piston 18 rises, air above the piston being vented to atmosphere through the slot 34 and the ball-check valve 33 and the adjustable valve 26. When the slot 34 no longer communicates with the cylinder 19, air above the piston 18 escapes to atmosphere through the adjustable valve 26 only and the rate of travel of the piston is reduced. The maximum pressure reached in the chamber 11 is determined by a preset relief valve 13. After a predetermined time interval the air supply through the pipe 20 is cut off and the pipe 20 is connected with the atmosphere so that the piston 18 commences its return stroke due to its own weight and a weight 21 on the bellows 12. As the piston 18 falls air is admitted to the upper part of the cylinder 19 through pistonrod slot 34, space 25 and flap valve 33. As the slot 34 passes below the top seal 24, air enters the cylinder only through the adjustable valve 26 so that the rate of downward travel of the piston 18 is reduced. The minimum pressure reached in the chamber 11 is determined by the setting of a relief valve 14. After a predetermined time interval air is again supplied to the cylinder 19 through the pipe 20 and the operation is repeated. In an alternative construction, the bellows 39 is actuated by a piston-rod 62 connected to a double-acting piston 35 in a cylinder 36. The piston-rod 62 slides on a rod 66 fixed to an apertured diaphragm between the bellows 39 and the chamber 37 which houses the breathing bag of the respiratory circuit. The upper and lower parts of the cylinder 36 are alternately connected with an air supply and with the atmosphere by means of lines 47, 38 respectively which are controlled by a switch device 40 and a timing device 56. When air is supplied beneath the piston 35 air above the piston 35 is vented to atmosphere and the piston rises. At the beginning of the upward stroke of the piston 35 air in the bellows flows to atmosphere through a slot 74 in the rod 66, a sealed space 69 between the rod 66 and the piston-rod 62 and a flap valve 73 in the lower part of the bellows 39. When the slot 74 no longer communicates with the bellows 39, escape of air from the bellows 39 is prevented and the rate of travel of the piston is reduced. After a time interval dependent on the setting of a device 56 in the air supply circuit, switch 40 causes the upper part of the cylinder 36 to be connected with the air supply and the lower part of the cylinder 36 to be connected with the atmosphere so that the piston falls. At the beginning of the downward stroke, a ball valve 71 in the lower part of the bellows opens and slot 74 connects the space 69 with openings 75 in the piston-rod 62 so that air enters the bellows 39. Towards the end of the downward stroke the connection between the slots 74 and the openings 75 is closed so that air cannot enter the bellows 39 and the rate of downward travel of the piston is reduced. After a predetermined time interval air is again supplied beneath the piston and vented from the space above it so that the cycle is repeated. Specification 781,747 is referred to.