THE EFFECT OF CHANGES IN ARTERIAL pCO2 ON ISOGRAVIMETRIC CAPILLARY PRESSURE AND VASCULAR RESISTANCES.

One study was designed to determine the effect of a changing arterial pCO2 on capillary permeability and pre- and postcapillary resistances. Experiments were carried out on isolated forelimbs of dogs perfused with blood equilibrated with different CO2 pressures in an isolated lung. Gas mixtures containing 0, 5, and 10 CO2 resulted in arterial mean pCO2 values of 12, 48 and 78 mm Hg. Isogravimetric capillary pressure Pci was measured using a modified Pappenheimer and Soto-Rivera technique. Results show the mean Pci rising from 13 to 14.7 mm Hg p 0.04 after pCO2 was increased from 48 to 78 mm Hg. When the pCO2 was lowered to 12 mm Hg, Pci fell to 10.1 mm Hg p 0.016. Precapillary resistance fell with an increased pCO2 and rose with a decreased pCO2. Effects of pCO2 were believed to alter the permeability of the capillaries due to a direct action on the capillary membrane. The observed changes in capillary permeability are interpreted as a protective mechanism opposed to effects of alterations of capillary hydrostatic pressure resulting from changes in blood pCO2. Author