GB866758A - Apparatus for controlling or assisting respiration - Google Patents

Abstract

866,758. Respiratory appliances. BRITISH OXYGEN CO. Ltd. Nov. 18, 1959 [Nov. 19, 1958], No. 37185/58. Class 81 (2). In apparatus for alternately forcing gas or a mixture of gases into a patient's lungs and permitting gases to be released from the lungs, a combined pressure control and timing means comprises a chamber having one wall formed as a pressure responsive member valve means coupled to the pressure responsive member for controlling the flow of pressurizing gas, means for admitting gas to the chamber at a pressure closely related to lung pressure during inhalation, the pressure responsive member being movable in response to a predetermined lung pressure to close the valve means, means for releasing gas from the chamber during exhalation whereby the pressure responsive member is movable to open the valve means, and adjustable loading means opposing movement of the pressure responsive member in the direction to close the valve means comprising first biasing means effective over the whole range of that movement and second biasing means effective only to oppose the final stages of that movement. As shown, pressurizing gas enters a valve chamber 3 at 5 and is discharged at 6, either to a patient's lungs or to compress a reservoir bag, through a valve 7. The valve is magnetically coupled to a bellows 9 mounted in a chamber 4 by means of a lever 17 carrying an armature 15 which co-operates with a magnet 13 secured to the free end of the bellows which constitutes the pressure responsive member. A fixed magnet 14 in the chamber 4 co-operates with an armature 16 carried by the lever 17. At the beginning of the inhalation phase, the bellows 9 is collapsed, the magnet 14 is in engagement with the armature 16 and the valve 7 is open. Gas is admitted to the bellows 9 through a non-return valve 11 to a pressure, closely related to lung pressure. Inflation of the bellows is opposed by springs 21, 22. The low rate spring 21 bears at one end against the bottom of the chamber 4 and at the other against a plate 19 secured to the free end of the bellows and pivoted about a pin 20. The high-rate spring 22 bears at one end against a cap 27 slidably mounted in a tubular member 24 and at the other against an adjusting screw 26. When a certain degree of inflation is reached the attraction between the armature 15 and the magnet 13 overcomes the attraction between the magnet 14 and armature 16 and closes the valve 7 with a snap-action. Gas escapes from the bellows 9 through an adjustable bleed 12, the duration of the exhalation phase being controlled by the force exerted by the spring 21 and the area of the bleed 12. The spring 22 acts on the plate 19 only during the final stages of inhalation and permits the pressure at which the apparatus switches from inhalation to exhalation to be varied independently of the duration of the exhalation phase.