Baroreceptor modulation of active cutaneous vasodilation during dynamic exercise in humans

The hypothesis that baroreceptor unloading during dynamic limits cutaneous vasodilation by withdrawal of active vasodilator activity was tested in sev en human subjects. Increases in forearm skin blood flow (laser-Doppler velo cimetry) at skin sites with (control) and without a-adrenergic vasoconstric tor activity (vasodilator only) and in arterial blood pressure (noninvasive ) were measured and used to calculate cutaneous vascular conductance (CVC). Subjects performed two similar dynamic exercise (119 +/- 8 W) protocols wi th and without baroreceptor unloading induced by application of -40 mmHg lo wer body negative pressure (LBNP). The LBNP condition was reversed (i.e., e ither removed or applied) after 15 min while exercise continued for an addi tional 15 min. During exercise without LBNP, the increase in body core temp erature (esophageal temperature) required to elicit active cutaneous vasodi lation averaged 0.25 +/- 0.08 and 0.31 +/- 0.10 degreesC (SE) at control an d vasodilator-only skin sites, respectively, and increased to 0.44 +/- 0.10 and 0.50 +/- 0.10 degreesC (P < 0.05 compared with without LBNP) during ex ercise with LBNP. During exercise baroreceptor unloading delayed the onset of cutaneous vasodilation and limited peak CVC at vasodilator-only skin sit es. These data support the hypothesis that during exercise baroreceptor unl oading modulates active cutaneous vasodilation.