Analysis of microvascular responses in the finger to changes in arm position during cold water stimulation.

We evaluated the extent to which the myogenic autoregulatory response was affected by sympathetic vasoconstriction in humans. The stimulus used to produce sympathetic vasoconstriction was the cold water immersion of a contralateral finger. The stimulus used to elicit myogenic response was gravitational potential energy change (GPEC), that is, arm position change, i.e., the raising and lowering of the upper extremity 40 cm above and below the heart level. The response was observed in terms of the changes in amplitude on a differential digital photoplethysmogram (delta DPG) during this maneuver with and without cold stimulation. The subjects were seven healthy males. During non-immersion, the delta DPG amplitude increased to 55.7 +/- 7.6% (SE) at the elevated position and decreased to -56.3 +/- 4.0% at the lowered position. Mean finger arterial blood pressure (MBP) decreased by 34.0 +/- 1.8% at the elevated position and increased by 39.9 +/- 3.3% at the lowered position. During immersion, the delta DPG amplitude was significantly (p < 0.05) decreased by 25-40, 33-57, and 33-38% at the heart, elevated, and lowered position, respectively. MBP increased by 5-9%, but heart rate was unchanged throughout immersion. These results indicate that the myogenic response of arterioles is not entirely abolished by the present sympathetic vasoconstrictor effect. Thus interactions between these two effects may maintain both systemic and local circulatory homeostasis.