Three-dimensional interactions of mean body and local skin temperatures in the control of hand and foot blood flows
Purpose Much is known about the control of blood flow, yet gaps remain concerning the interactions of deep-body and peripheral thermal feedback. In this experiment, changes in the vascular tone of the hands and feet were mapped to demonstrate the separate and combined influences of mean body and local skin temperature changes. Methods Eight males participated in three trials. Three pre-experimental conditions were established via water immersion (oesophageal temperatures: 36.1, 37.0, 38.5 °C), with core and mean skin temperatures then clamped (water-perfusion garment) whilst five thermal treatments were applied to the right hand and left foot (5, 15, 25, 33, 40 °C). This yielded 15 thermal combinations under which hand and foot blood flows were measured (displacement plethysmography). Results Lower volume-specific blood flows were observed at the foot for almost all temperature combinations. When thermoneutral and moderately hyperthermic, the cutaneous thermosensitivity of the hand was significantly greater: thermoneutral: 0.2 vs. 0.1 (foot) mL 100 mL−1 min−1 °C−1 (P < 0.05); moderate hyperthermia: 0.4 vs. 0.2 (foot) mL 100 mL−1 min−1 °C−1 (P < 0.05). The hand was 13 times more responsive to core temperature elevations than an equivalent local skin temperature change. For the foot, this thermosensitivity differed by a factor of 26. Conclusion These observations identified the hands as heat radiators, with the feet resisting heat loss, and reinforce the dominance of central thermal feedback, particularly in controlling foot blood flow. However, thermosensitivity to local skin temperature changes was highly plastic, site-specific and dictated by thermal and regional variations in vaso- and venoconstrictor tone.