Acute hemodynamic effects of total head-down body tilt and hexamethonium in normal and pulmonary emphysematous subjects.

Abstract

Abstract 1.1. The influence of a 35-degree total head-down body tilt and the modifying effects of acutely administered hexamethonium on the cardiac output, the central venous and the brachial artery pressures has been studied in 5 normal individuals and in 5 subjects with pure, emphysematous pulmonary hypertension. 2.2. Tilting sustained for 15 minutes produced consistent slight decreases in the heart rate and measurable increases in central venous and brachial artery pressures and in total pulmonary resistance of all subjects, without alteration of the cardiac output. 3.3. Intrapulmonary arterial administration of hexamethonium during sustained tilt produced a partial reversal of all phenomena, again without alteration in the cardiac output. In this phase a significant difference was noted between the two groups of subjects, relevant to the response of the heart rate and the brachial artery pressure. 4.4. The data indirectly suggest that the cardiopulmonary pressure changes induced by sustained head-down tilting may be the resultant of an increased cardiopulmonary blood volume (without a change in the cardiac output), active vasomotion in the pulmonary vasculature, and a possible increase in the intrapleural pressure. 5.5. No alternative explanation is offered for the opinion expressed by others that the immediate increase in brachial arterial pressure following head-down tilting is due to a passive hydrostatic phenomenon followed later by a secondary vasodepressor readjustment.