Application of amplitude-based and slope-based algorithms to determine beat-to-beat finger arterial compliance during handgrip exercise

Beat-to-beat finger arterial compliance C is calculated applying two different estimates. The amplitude-based algorithm Camplit = ΔV/ΔP determines compliance as a ratio of finger volume and pressure pulses, whereas the slope-based technique Cslope = 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 Ptransm = 0). The results of the study demonstrate that both compliance estimates gave analogous responses to light physical exercise (r = 0.94, p < 0.002). At the same time, the values of Cslope were systematically higher than those for Camplit (the slope of the regression line equalled 1.11). Even at Ptransm = 0, a variation of 13 mmHg in the pulse pressure caused an 8% modulation in Camplit (p = 0.03). The slope-based estimate was less sensitive to pulse pressure changes.