Noninvasive method for estimating the mean capillary pressure and pre- and postcapillary resistance ratio in human fingers.

Abstract

A noninvasive method for estimating the mean capillary pressure Pcap and the pre-and postcapillary resistance ratio Rv/Ra in human fingers is described. Volume change in a finger segment was detected with a transmittance-type infra-red photoelectric plethysmograph during a gradual and linear increase in occluding cuff pressure. There was an inflection point in the volume curve which would be produced by the difference in the compliance between the arterial and venous vascular bed in the segment. This transitional point was assumed to represent the complete compression of the venous vascular bed at the cuff pressure level. Thus Pcap was defined as the cuff pressure corresponding to the inflection point. Rv/Ra was calculated from the Pcap, the venous pressure Pv and the mean arterial pressure Pam. The latter two pressures, Pv and Pam, were also indirectly and simultaneously measured by the compression pressure of another cuff and by our new type of volume oscillation method, respectively. The values of Pcap and Rv/Ra were in good agreement with those reported by other investigators.