Patent GB-1410258-A (GB)
Title: Device for warning of abnormal flow conditions in artificial  ventilation of the lungs
IPC: A61M16/20
Filed: 1973-01-26
Abstract: 1410258 Warning devices in respiratory systems DRAGERWERK AG 26 Jan 1973 [26 Jan 1972] 4242/73 Heading AST Warning Device:-A device (51), Fig. 1, (not shown) for warning of abnormal flow conditions in artificial ventilation of the lungs comprises pressure monitoring means adapted to actuate warning means (15) when the average pressure in a ventilation duct (50) departs significantly from its valve during normal flow conditions. The monitoring means comprises a throttle 6, Fig. 2, connecting the duct (50) to a chamber 7 and a switch (13) which includes a rocker 24 which can be set to a position corresponding to the pressure during normal flow. The chamber 7 is connected to a pressure gauge 8 and a differential-pressure-responsive unit (10). An electrical control unit (14) is connected to the switch (13), the unit (10), the warning means (15) which may be optical and/or acoustical, and an electromagnetic valve (18) which controls a duct (16) in parallel with a duct (5) which connects the duct (50) with the throttle 6. The duct (16) has a throttle (17) having a greater crosssection than the throttle 6. The device (51) is connected to a respiratory apparatus (1) via an inhalation duct (2) and an exhalation duct (3). Switch: The switch (13) comprises a cell 19 having a flexible diaphragm 20 which abuts one arm of a two-arm lever 22 which is mounted on a bearing 23 and biased by a spring 21. The rocker 24 is also mounted on the bearing 23 and carries two switches 25, 26 connected to the warning unit (15). The other arm 27 of the lever 22 has a notch 28 which engages the head of a coupling pin 29 which is slidably mounted in the rocker 24 and supported by a block 31 which abuts a fixed part 32 to arrest the rocker 24. An electromagnet 33 operates a lever 35 against the bias of a spring 36 and causes the pin 29 to engage the notch 28. Alternatively, the monitoring unit may comprise a pneumatic electrical transducer which is connected to a capacitor whose charge is dependent upon the pressure. Differential-Pressure Responsive Unit: The unit (10) comprises compartments 37, 39, Fig. 3, separated by a diaphragm 36 which is biased by a spring 38 towards the compartment 39 which is connected via a throttle 40 to a compartment 41 which is bounded on one side by a diaphragm 42 which is biased by a spring 46 towards the compartment 41 and which operates a switch 48. The compartment 41 has an outlet valve 43 having a movable member 44 which bears on the diaphragm 36 through a rod 45 which passes through a wall of the compartment 39 in gas-tight manner. Operation: The pin 29 is initially caused, by the electromagnet 33, to engage the notch 28, thereby coupling the rocker 24 and the lever 22. The rocker 24 moves to a position corresponding to normal flow in the ventilation system, whereupon the pin 29 disengages from the notch 28 so that the block 31 abuts the fixed part 32 and arrests the rocker 24. Any subsequent significant pressure changes in the chamber 7 causes the lever 22 to pivot and close one of the switches 25, 26 and operate the warning device (15). In normal operation, the peak pressure in a conduit 11, connecting the unit (10) to the conduit (5), is greater than the pressure in the chamber 7 so that the diaphragm 36 moves to compress the sprung 36 and open the valve 43 so that the gas can escape. However, if said peak pressure falls below the pressure in the chamber 7, the valve 43 is biased to a closed position so that after some time, pressure builds up in the compartment 39 and is transmitted to the diaphragm 42 which closes the switch 48 and operates the warning device (15). The conduit (16) serves to rapidly equalise the pressure in the chamber 7 and the duct (50).