Patent GB-745307-A (GB)
Title: Improvements in or relating to respiratory apparatus
Inventor: HIRSCH CHARLES
IPC: A61M16/00
Filed: 1953-09-18
Abstract: 745,307. Artificial respiration apparatus. SIEBE, GORMAN & CO., Ltd. Sept. 18, 1953, No. 25869/53. Class 81(2). [Also in Group XIX] A warning device for iron lungs comprises pressure responsive means operating in rhythm with pulsations of the pressure controlling mechanism to open and close a control circuit provided with slow acting means effective to ensure the operation of an alarm only after the pressure within the chamber has altered from a predetermined value by a predetermined amount for a predetermined period. A pressure responsive means, Fig. 1, comprises an inlet 1 connected with a source of air pressure pulsations and with a copper-beryllium capsule 2 forming bellows. On one face of the capsule 2 is mounted a bridge carrying a contact 4. A second contact 8 is provided on a resilient member 7 and is disposed in alignment with the first contact 4. The member 7 is adjustable towards and away from the first contact 4 by a calibrated screwthreaded member 9 which extends into a block 10 so as to bear on the member 7 and is held in position by a screw 11. The pressure responsive means 12, Fig. 3, is connected in part of the control circuit so that one contact is earthed or connected to a common terminal and the other contact is connected to a secondary coil 13 which is coupled with a primary coil 36 in an alternating current mains circuit. In normal operation of the iron lung, the pressure responsive means is adjusted so that the contacts 4, 8 make and break part of the control circuit according to the air pressure pulsations reaching the capsule 2. The spacing of the contacts 4, 8 is adjusted so that in the event of the negative pressure falling below a predetermined minimum e.g. 5 cms. water gauge, contact is not made between the contacts 4, 8 and part of the control circuit, which forms a pressure variation detecting means enclosed by chain lines 41. including a condenser 15 e.g. of 4 micro farads, shunted by a resistance 16 e.g. of 3 megohms which is earthed or connected to the common terminal through a resistance 17, and connected with the grid 18 of a thyratron 19, is broken. The condenser 15 then discharges. If the negative pressure falls below the predetermined minimum for more than a predetermined period e.g. 15-30 seconds, the condenser 15 discharges sufficiently for the thyratron 19 to strike so that a circuit including a second secondary coil 22 also coupled with the mains primary coil 36, and a relay 21 is closed. Energisation of the relay 21 closes contacts 24 which close a circuit including a third secondary coil 25 and an audible warning device 30 or a visual warning device 32. A switch 31 in the warning circuit is kept closed so that either a visual or an audible warning may be given. The doors 33, 34, 35 of the iron lung are arranged in the warning circuit so that in the event of any one of them being open only a visual warning is given. The third secondary coil 25 is also connected with a rectifier 27 and a relay 28 which when energised holds open contacts 29 which connect a battery 39 with the warning circuit when a switch 37 in the mains circuit is connected to bring the warning system into operation, a switch 38 ganged with it and connecting the battery 39 to earth is also closed. If the mains supply fails, the relay 28 fails to hold the contacts 29 apart so that the battery 39 energises the warning circuit and an audible or visual warning is given dependent on the position of the switch 31. In an alternative construction (not shown) four circuits each forming pressure variation detecting means similar to that shown in Fig. 3 and including a pressure responsive means are provided so that audible or visual warning is given due to (a) loss of negative pressure (b) loss of positive pressure, (c) increase of negative pressure and (d) increase of positive pressure of the air pressure pulsations in the iron lung. Pressure responsive means (not shown), similar to that described above or having valves in the inlet to cut off half the pressure pulsation cycle are provided with contacts disposed so that the control circuit is broken for each of the above changes in the air pressure pulsations.