Beat-to-beat finger arterial compliance C is calculated applying two different estimates. The amplitude-based algorithm C(amplit) = DeltaV/DeltaP determines compliance as a ratio of finger volume and pressure pulses, whereas the slope-based technique C(slope)=dV/dP is based on the calculation of the slope of the pressure-volume relationship from the first derivatives dV/dt and dP/dt of the recorded volume and pressure pulses at the point of their maximum slope. The finger arterial pressure and volume changes in 11 healthy volunteers during two successive handgrips were recorded by applying the Finapres monitor and the UT9201 physiograph, respectively. The latter instrument automatically keeps counter pressure in the measuring cuff equal to the mean intra-arterial pressure (transmural pressure P(transm) = 0). The results of the study demonstrate that both compliance estimates gave analogous responses to light physical exercise (r = 0.94, p0.002). At the same time, the values of C(slope) were systematically higher than those for C(amplit) (the slope of the regression line equalled 1.11). Even at P(transm) = 0, a variation of 13mmHg in the pulse pressure caused an 8% modulation in C(amplit) (p = 0.03). The slope-based estimate was less sensitive to pulse pressure changes.
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