Much larger transcapillary hydrodynamic conductivity in skeletal muscle and skin of man than previously believed.

The capillary filtration coefficient (CFC) in the human forearm, determined with the 'venous occlusion' method, was found to be about 0.005 ml min-1 100 ml-1 soft tissue mmHg-1 when capillary pressure (Pc) was raised by about 30 mmHg, a finding in accordance with previous literature. With gradually smaller increments of Pc, however, the calculated CFC became gradually larger to reach maximal values of about 0.05 ml min-1 100 ml-1 mmHg-1 at increases in venous pressure that raised Pc by only 1.5-2 mmHg. It is suggested that these high CFC values, obtained at increases of intravascular pressure so low as to ensure minimal interference with the normal circulation, reflect the true prevailing transcapillary hydrodynamic conductivity in the tissue. The low CFC values during high increases in capillary (microvascular) pressure, on the other hand, seem to represent serious underestimations of the true CFC as a result of experimentally induced undesired active smooth muscle constrictor responses and/or passive deterioration of capillary exchange function. The conclusion is therefore reached that CFC in skeletal muscle and skin in man might be about 10 times higher than previously believed.