Forearm arterial pressure-volume relationships in man.

Pressure-volume (p-V) relationships of a segment of the forearm circulation have been measured in nine male healthy subjects. Forearm volume was measured using electrical impedance plethysmography, arterial transmural pressure by subtracting mean arterial pressure measured contralaterally in a finger from the pressure in a cuff placed over the sensing electrodes of the plethysmograph. A special two-phase measurement waveform was designed with which cuff pressure was first increased step wise to a suprasystolic level and held at that level for 120 s, then ramped down to zero pressure in another 300 s. The step phase inflation allowed us to estimate the parameters of the interstitial liquids and total blood compartments. The total blood compartment amounted to 6.2 ml per 100 ml of tissue. The ramp phase deflation allowed us to discriminate between a first phase in which only the arteries refilled and a second phase in which the veins also distended. An arctangent function was fitted to the first phase arterial p-V relationship, describing it in model form. Total arterial volume per 100 ml of tissue amounted to 3.8 ml at physiological pressures, total arterial compliance of the forearm per centimetre length to 19.5 microliter kPa-1 cm-1 (2.6 microliter mmHg-1 cm-1) at physiological pressures, and to 340 microliter kPa-1 cm-1 (45 microliter mmHg-1 cm-1) maximum compliance at the lower, inflection point pressures. These values are in general agreement with the literature. Pulse wave velocity cannot be computed reliably from these data.