| Abstract: | Effective vascular compliance was measured repeatedly in dogs without circulatory arrest utilizing a closed-circuit venous bypass system and constant cardiac output. Compliance, determined by the delta V/delta P relationship at the end of a 1-min infusion of 5% of the circulating volume into the inferior vena cava, was independent of the initial venous pressure, total circulating volume and systemic arterial pressure. It remained constant over a 3 h experimental period at 1.55 plus or minus 0.05 ml (mm Hg)-1-kb-1 body weight. Elevation of mean left atrial pressure and mean pulmonary arterial pressure by gradual aortic constriction was associated with a large and significant reduction in vascular compliance to a value of 1.14 plus or minus 0.06 ml (mm Hg)-1-kg-1 after 2 h. This reduction was independent of the initial venous pressure and total circulating volume but was associated with the changes in left atrial and pulmonary artery pressures and an increase in plasma catecholamine concentrations. The mechanism responsible for the reduction in effective compliance is not clear from the present experiments. Increased circulating catecholamines and sympathetic nerve traffic resulting from baro- and volume receptor stimulation in the vascular tree may be the causative mechanism. |
