Cardiopulmonary baroreflex control of forearm vascular resistance after acute blood volume expansion

We report the stimulus-response characteristics of cardiopulmonary (CP) baroreflex control of forearm vascular resistance (FVR) in young adult male volunteers before and after: 1) blood volume expansion (8 ml/kg infusion of 5% human serum albumin solution, n = 5) and 2) a redistribution of blood volume toward the heart (6 degrees head-down tilt (HDT), n = 6). We assessed the relationship between reflex stimulus (i.e., changes in central venous pressure (CVP] and response (i.e., FVR) during unloading of CP mechanoreceptors with lower body negative pressure (0 to -20 mm Hg). Changes in CVP were estimated from changes in venous pressure of a large peripheral vein of the dependent arm with the subject in the right lateral decubitus position. In all conditions, reflex forearm vasoconstriction occurred in response to a reduction in estimated CVP. The absolute change in FVR per unit of CVP was reduced from -4.24 +/- 1.68 to -2.15 +/- 1.16 units/mm Hg (p less than 0.05) following blood volume expansion but was similar before (-3.34 +/- 0.89 units/mm Hg) and during 6 degrees HDT (-3.30 +/- 0.92 units/mm Hg). The reduced sensitivity of the CP baroreflex following volume expansion was manifested primarily as a smaller FVR response to LBNP (p less than 0.05). Blood volume expansion and 6 degrees HDT increased resting estimated CVP by 1.5 and 0.9 mm Hg, respectively (p less than 0.05) and resting levels of FVR decreased slightly.(ABSTRACT TRUNCATED AT 250 WORDS)