Systemic and pulmonary hemodynamic responses to intracranial hypertension

Experiments were conducted in anesthetized, vagotomized, and open-chest dogs. Total heart bypass was performed to perfuse the systemic and pulmonary circulations with constant flow. The venous outflows were diverted into reservoirs. We studied the simultaneous changes in systemic vascular resistance (SVR) and capacity (SVC) as well as pulmonary vascular resistance (PVR) and capacity (PVC) during a period of intracranial hypertension (ICH). In 20 dogs with an intracranial pressure of 164 +/- 12 mmHg, SVR increased by 110% and SVC decreased by 8.4 +/- 1.2 ml/kg. The increase in PVR reached 69%, and the decrease in PVC amounted to 1.24 +/- 0.40 ml/kg body wt or 9.7 +/- 3.9 ml/100 g lung wt. The results indicate that ICH exerts profound effects on both systemic and pulmonary resistance and capacitance vessels. An analysis from the pulmonary blood volume change suggested that the pulmonary vascular compliance was significantly reduced by ICH from a control value of 0.33 +/- 0.06 to 0.26 +/- 0.05 ml X mmHg-1 X kg-1. In the pulmonary circulation, an elevation of left atrial pressure with lung volume expansion attenuated the resistance response, while it increased the capacity reduction. When pulmonary blood volume was kept constant by a constant venous outflow equal to the arterial inflow, the response of capacitance vessels to ICH increased both pulmonary arterial and venous pressures associated with a slight change in PVR. These findings suggest that an increase in pulmonary venous pressure with a constant or increased blood volume reduced the ICH-induced change in resistance.