Patent GB-1534078-A (GB)
Title: Pneumatic pump monitor
IPC: A61M60/569
Filed: 1976-04-30
Abstract: 1534078 Pneumatic blood pump THERMO ELECTRON CORP 30 April 1976 [9 Jan 1976] 17766/76 Heading G1N In a pneumatically driven 3 blood pump 4-6, driven via a stroke volume limiter 2 containing a diaphragm 9, the signal from a pressure transducer 14 within the "closed system" beneath the diaphragm 9 together with the signal from a linear displacement transducer 18, associated with the diaphragm's movements within the limiter 2, are processed to provide information about the stroke volume, flow-rate and beat rate of the pump. The blood pump may be of the type disclosed in Specification 1532066 and the stroke volume limiter may be of the type disclosed in Specification 1532719. The blood pump 1 comprises a flexible bladder 4 enclosed by a rigid housing 5. A rhythmical injection of gas between the bladder 4 and the housing 5 repeatedly collapses the bladder to produce pumping action in co-operation with one-way valves 6 located at inlet and outlet conduits 7. The stroke volume limiter 2 controls the amount of gas injected into the blood pump. The limiter comprises a chamber 8 enclosing the diaphragm 9 and a circumferential portion 10 of the diaphragm 9 creates a seal between a centrally rigid portion 9' of the diaphragm 9 and the chamber 8. The pressure transducer 14 supplies a calculator 15 which computes the volume lost V 1  to the system due to compression of the gas. Simultaneously the linear displacement transducer 16 supplies a calculator 16 which computes the amount of compressive displacement Vd being introduced into the system. The two signals are fed to a calculator 19 that subtracts Vi from Vd to provide a sinusoidal signal proportional to the volumetric state of the bladder 4. The sinusoidal signal is fed to a circuit 26 which operates on it to set the voltage of the low peaks or troughs to zero so that the voltage reading of the high peak is directly proportional to the stroke volume Vb. Measured parameters derivation. The stroke volume signal may be outputted via a manually operated selector switch 28 and an A/D converter 29 to a display 37. The converter 29 extracts the stroke volume information when signalled to read the voltage at the precise moment of each individual "high peak" of the signal 27 by a display trigger 36. The display trigger 36 is supplied with signals via a trigger selector switch 35 which is ganged with the output selector switch 28. In this case the signal from a bi-stable flip-flop 34 actuated by a negative slope detector 32 and a positive slope detector 33 connected as shown, are used. The flip-flop 34 produces rectangular pulses which change state on the occurrence of a high peak in the bladder analogue signal 27. The flip-flop 34's signal is also fed to a "Beats per minute" calculator 38 which can be displayed via the output switch 28 and the A/D converter 29. The converter is controlled by the display trigger 36 as before only signals from a "Beats-perminute" trigger 39 is used. The signals from the trigger 39 ensures that the sampling for display takes place with a slight delay after each high peak point of the Vb signal 27. The high peak value of the signal 27 is monitored and stored by a peak follower 30 and may be displayed, as before, or it may be multiplied in a circuit 40 with the signal from the "Beats-per-minute" calculator 38 to get a signal proportional to the flow-rate which may also be displayed. A detailed circuit diagram Fig. 3 (not shown) of the block diagram shown in Fig. 1 is disclosed.