Patent GB-1375718-A (GB)
IPC: A61M16/00
Filed: 1971-11-29
Abstract: 1375718 Lung ventilator MEDICAL DEVELOPMENTS Ltd 14 Feb 1973 [29 Nov 1971] 55328/71 Heading A5T Ventilator: A ventilator comprises means for automatically and cyclically supplying a tidal volume of gas to a conduit 22 for connection to the lungs during a first phase, a reservoir 67 connected with the conduit 22 by a pipe including a first valve 50, means for closing the valve 50 during the first phase and opening it on completion of the first phase and means operable to withdraw gas from the reservoir 67 and, during a second phase, apply a subatmospheric pressure to the conduit 22 after a predetermined delay, following completion of the first phase, when the reservoir 67 is empty. Gas supplied to an inlet 10 is passed by a tap 12 to pipes 14 or 16 which correspond to automatic or manual operation respectively. In the automatic mode gas passes through the pipe 14 into the means for supplying a tidal volume of gas to the conduit 22, which is an inspiration bellows 30, through valve means 32 and a needle valve 31 and into the conduit 22. The valve means 32 is operated, through a linkage 33 by the bellows 30 which is linked with an expiration bellows 66 which is connected to an exhaust valve 70 and the expandable reservoir 67 through a valve 68. The bellows 30 is connected to an expandable reservoir 26 through the valve 50 and the valve means 32. The ventilator operates at 20 cycles per minute and the first and second phases and the delay are each of about one second duration. Manual operation is effected by connecting the inlet 10 to the pipe 16 which is fitted with a safety valve 20 and a pressure gauge 18 and setting a tap 24 to connect the conduit 22 with the reservoir 26. Bellows: The bellows 30 is coupled to a lever 40 which is biassed by a spring 44 and pivots at 42. A lever system 54 couples the bellows 30 and 66 such that they inflate and deflate simultaneously and comprises a spring 62 and levers 56, 58, 60 and 64. The rate at which the bellows 66 inflates is adjustable by a screw 63 which is used to adjust the relative positions of the levers 40 and 56. The maximum volume of the bellows 66 is greater than that of the bellows 30. Valve Means: The valve means 32 comprises valves 46, 48A and 48B operated by levers 33, 34 and 36 whose relative positions are adjusted by a thumb screw 38. The lever 40 strikes the levers 34 and 36 to maximum and minimum inspiration volumes respectively, determined by the position of the thumb screw 38, to open and close the valve 46 respectively. The valves 48A and 48B respectively open and close at the maximum inspiration bellows volume and close and open respectively at the minimum inspiration volume. Operation: When the volume of the bellows 30 is a minimum, the valves 46 and 48A are closed and the valve 48B is open. Gas from the inlet 10 inflates the bellows 30 until the maximum volume is reached when the valves 46 and 48A are opened and the valve 48B closes. The spring 44 deflates the bellows 30 which exhausts through the valve 46 and the needle valve 31 into the conduit 22 which is connected to a face mask, while the valve 50 is kept closed. At the end of this, the inspiration phase, the valves 46, 48A and 48B assume their original conditions and the patient breathes out through the now open valve 50 into the reservoir 67. The bellows 30 and 66 are meanwhile expanding again and the bellows 66 applies a reduced pressure on one side of the valve 68 which opens when the pressure differential across it is sufficiently large. The bellows 66 then exhausts the reservoir 67 and when this is empty, exhausts the patients' lungs, during the expiration phase, by applying a subatmospheric pressure to the conduit 22. The time to exhaust the reservoir 67 constitutes the delay time. The maximum volume of the bellows 66 is limited by the spring 62 which acts as a lost-motion device to limit the maximum value of sub-atmospheric pressure generated by the bellows 66. When the bellows 30 and 66 collapse, the bellows 66 exhausts through the valve 70. In an alternative embodiment, a valve between the bellows 66 and the reservoir 67 controls the maximum value of the subatmospheric pressure.