Carotid and cardiopulmonary baroreceptor control of splanchnic and forearm vascular resistance during venous pooling in man.

1. This study evaluated the contribution of carotid and cardiopulmonary baroreceptors to reflex splanchnic and forearm vascular adjustments during venous pooling in man. We compared (a) responses to lower body suction which produces venous pooling with (b) responses to lower body suction plus simultaneous application of neck suction. The rationale was that simultaneous application of neck suction, which stretches carotid baroreceptors, would minimize the contribution of carotid baroreceptors to circulatory adjustments produced by lower body suction.2. Lower body suction at 40 mmHg decreased central venous pressure and arterial pulse pressure and increased forearm vascular resistance (plethysmography), splanchnic vascular resistance (indocyanine green dye clearance), and heart rate. Simultaneous application of neck suction prevented the tachycardia and most of the splanchnic vasoconstriction during lower body suction, but did not significantly attenuate the forearm vasoconstriction.3. The major findings in this study are first, that the splanchnic vasoconstrictor response during venous pooling is mediated primarily through carotid baroreceptors, and secondly, that carotid and cardiopulmonary baroreceptors produce strikingly contrasting and non-uniform regional vascular responses during venous pooling. Cardiopulmonary baroreceptors exert the predominant influence on forearm vascular resistance, but appear to have only a minor influence on splanchnic vascular resistance. Carotid baroreceptors produce most of the splanchnic vasoconstriction during venous pooling. but have a minor role in the forearm vasoconstriction.