Apparatus for measuring the urea between a fluctuating signal and an inclined baseline

Abstract

Abstract 1340542 Electric analogue calculating BARR & STROUD Ltd 1 May 1972 [30 June 1971] 30573/71 Heading G4G [Also in Division G1] An apparatus for measuring the shaded area between a waveform and a sloping baseline ac in Fig. 34, comprises an integrator for determining the area between the waveform and a horizontal baseline ab coincident at one end a with the sloping baseline, means for measuring the length of the horizontal baseline and means for measuring the distance bc, means for multiplying the length ab and distance bc and halving the product to obtain the area of the triangle abc and means for summating, with appropriate polarities, the area of the triangle and the area obtained by the integrator. The apparatus described is for use in determining cardiac stroke volume and output, in which case points a and b are successive diastoles of the heart beat. Circuitry is described for detecting these successive diastoles as an electrical signal and the voltage between them represents distance bc. At the instant of diastole a a ramp generator is started and it is stopped by the occurrence of diastole c at which time its voltage level is proportional to length ab. The voltage difference between the distoles and the final voltage of the ramp generator are multiplied and halved so that a signal representing the area of triangle abc is obtained. This signal is then subtracted from the output of an integrator which has measured the area between baseline ab and the waveform. A signal representing the shaded area is thus obtained. The shaded areas of a sequence of heart beats, e.g. over 30 seconds, can be summed to give the volume of blood pumped over that period. Reference has been directed by the Comptroller to Specification 1,270,761.

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