Patent GB-781747-A (GB)
Title: Lung ventilating apparatus particularly for administering anaesthetics
IPC: A61M16/00
Filed: 1955-12-05
Abstract: 781,747. Administering anaesthetics. AIRSHIELDS, Inc. Dec. 5, 1955 [Jan. 31, 1955], No. 34756/55. Class 81 (2). A portable lung ventilation apparatus for use in administering anaesthetics and operated by compressed air or gas comprises a chamber 12, Fig. 1, of transparent material, e.g. glass or plastic, in which succeeding phases of position and negative pressure are effected by a bellows 43 and enclosing a flexible bag 17 containing anaesthetic gas and connected by tubes 18, 18a, and an intermediate fitting having a pressuregauge 20 with a two-way valve 21 connected bv a flexible tube 25 to the anaesthesia machine and to a flexible bag 17a also containing anaesthetic gas, and which may be operated manually in the event of failure of the compressed air means operating the bag 17. The duration of the pressure phases in the chamber are controlled by a timing device 50 operated by compressed air or gas, and the magnitude of the positive and negative pressures are maintained at pre-set values by valves 27 and 28 mounted on the chamber, said valves controlling respectively the discharge of air from and the admission of air to the chamber. The timing device comprises superposed sections 56, 57, 58, Figs. 6, 7, having between the sections 56, 57 a chamber 65 and between the sections 57, 58 a chamber divided into compartments 67, 68 by a snap-over diaphragm 69 loaded by an adjustable spring 70. The chamber 65 communicates through an aperture 64 in a fitting 61 controlled by a spring-loaded ball valve 63 and radial ports 62 with a bore 60 connected to a constant pressure gas regulator 53 of known type having a pressure gauge 55 and connected by a pipe 52 with a compressed oxygen tank 51. The chamber 65 also communicates through a pipe 49 with the lower end of a cylinder 48 having a piston with a rod 46 connected to the heavy movable end-plate 45 of the bellows 43, the upper apertured endplate of which is secured to the correspondingly apertured base-plate 16 supporting the chamber 12. The chamber 65 also communicates through a bore 76 in a rod 73 secured to and extending through the diaphragm with the compartment 68, which is open to the atmosphere through a duct 77 in the section 58, and with the compartment 67 through a passage 79 in the section 57 controlled by a needle valve 81. With the diaphragm 69 in the position shown in Fig. 6, the ball valve 63 is displaced from the aperture 64 by the rod 73 and oxygen flows from the tank 51 into the chamber 65 and thence via pipe 49 to the cylinder 48 thus raising the piston rod 46 and closing the bellows 43 and increasing the pressure in the chamber 12, thus forcing gas from the bag 17 to the lungs of a patient. During this time, oxygen bleeds from the chamber 65 through the passage 79 into the chamber 67, the pressure in which builds up until the diaphragm snaps over into the position shown in dotted lines 69a in Fig. 7. At this moment, the rod 73 is raised out of contact with the ball valve which closes on the aperture 64, thus shutting off the flow of oxygen to the chamber 65 the pressure in which falls immediately to atmospheric. The pressure beneath the piston in the cylinder 48 also falls to the same value and the piston descends under the weight of the plate 45 of the bellows which opens and reduces the pressure in the chamber 12 so that the bag 17 expands and withdraws gas from the patient's lungs. During this time, the pressure in the compartment 67 slowly falls until a point is reached at which the diaphragm 69 snaps over into its lower position and by displacing the ball valve from the aperture 64 initiates automatically another positive pressure phase in the chamber 12. The total period of succeeding positive and negative pressures in the chamber is regulated by the needle valve 81, and the length of these phases by the loading on the spring 70. The maximum positive pressure in the chamber 12 is determined by the spring loading on a disc 31, Fig. 3, covering a port 30 in the top of the chamber, while the maximum negative pressure is regulated by a spring-loaded disc 37, Fig. 4, which opens when the pressure in the chamber exceeds a desired value and permits the admission of atmospheric air through a port 36 in the disc chamber and ports 42 in the disc chamber and the top of the chamber 12.