Patent GB-511559-A (GB)
Title: Improvements relating to analgesic apparatus
IPC: A61M16/10
Filed: 1938-05-30
Abstract: 511,559. Anaesthetic apparatus. SVENSKA AKTIEBOLAGET GASACCUMULATOR. May 30, 1938, Nos. 16106 and 16107. Convention dates, May 31, 1937, and Aug. 30, 1937. [Class 81 (ii)] Anaesthetic apparatus, partly controlled by the patient and more especially for use during childbirth, includes automatic valve means adapted to release a measured dose of anaesthetic gas, e.g. nitrous oxide, for inhalation by the patient and thereafter to prevent inhalation of a further dose until a predetermined interval has elapsed, whereby excessive inhalation cannot produce an overdose of gas. In Fig. 1, gas flows from cylinder 1, via pipe 2, pressure gauge 3, pressure regulator 4, throttle valve 7 and pipe 5 to valve chamber 6. The latter contains two valves 11, 12 carried by bridge 13 pivoted at 16 and connected by link 17 to diaphragm 14. The other arm of the bridge 13 serves as an armature for magnet 18. In operation, the valves 11, 12 being displaced to the right and being held in this position by magnetic contact between the lower end of the bridge and the left hand arm of the magnet, gas passes into chamber 15 and bladder 20 at a rate determined by valve 7. When the bladder is expanded to the extent allowed by member 21 and adjusting screw 22, the increasing gas pressure deflects diaphragm 14 to the left, as soon as it exceeds the magnetic attraction, thereby closing valve 11 and opening valve 12, whereby the patient can inhale the gas through valves 12, 23, tube 25 and mouthpiece 26. On protracted inhalation, the diaphragm 14 moves to the right thereby closing valve 12, valve 23 closes, and valve 27 opens so that the patient breathes in air. When necessary, the doctor can speed up the filling of chamber 15 and bladder 20 by operating a valve 10 connected to a bypass 8. In Fig. 2, the gas passes to bladder 20 through reducing valve 4 and throttle valve 28, the extent to which the bladder is inflated being controlled by adjusting screw 22, and a support attached to a lever 29 and provided with a stud 30 which can contact with arm 31. When the bladder is exhausted, a weight 36 will have caused-lever 29 to have turned counterclockwise to close electrical contacts 32, 33, current from battery 34 flowing through the contacts, relay 35 and resistance 43, valve 38 being held closed by the armature 42 of the relay. The bladder fills quickly and causes contacts 32, 33 to open. The relay 35 is, however, still energised by condenser 44, and keeps valve 38 closed, say for 1-2 minutes, the time being regulated by adjustment of resistance 43. During the time that the valve 38 is closed, the patient can only breathe in air through valve 27. Valve 28 is adjusted for a pressure of say 5 mm. above atmospheric, and valves 38 and 27 to open at say 10 mins. and 15 mins. respectively. The doctor can quickly administer gas to the patient by pressing valve button 47, thereby bypassing valve 28 and at the same time closing contacts 46 to short circuit relay 35 so that valve 38 is not held in the closed position. In Fig. 3, the diaphragm 14 is linked to a pivoted lever 49 which serves to operate contacts 52, 53 in a circuit comprising a battery 56 and a relay consisting of an electro-magnet 57 in series with an adjustable resistance 58 and both in parallel with a condenser 59. The magnet 57 acts upon valve bridge 13 and contact 60. Immediately before and for some time after the initial admission of gas from cylinder 1, the battery circuit is closed, the magnet 57 being magnetised under a certain delay produced by short-circuit winding 61. This lagging period enables condenser 59 to be charged. When the relay is fully magnetised contact 60 is opened, but the relay winding still receives current from the condenser 59 through resistance 58 which is adjusted so that the relay is energised for a pre-determined period. During this time, due to the action of the magnet on bridge 13, valve 11 is open and valve 12 closed, and the bladder 20 is filled. The pressure in the diaphragm chamber and bladder then rises, and the attraction of the magnet 57 decreases, until a point is reached at which the pressure on the diaphragm exceeds the attraction of magnet 57 and the left-hand arm of magnet 18 whereupon the diaphragm moves into the position shown, opening valve 12 and closing valve 11. A mixing valve may be incorporated in the apparatus by means of which the anaesthetic gas is mixed with oxygen, nitrogen or air. The diaphragm may be replaced by a bellows system, and the bladder by another means of variable volume.