15° Head-down tilt attenuates the postexercise reduction in cutaneous vascular conductance and sweating and decreases esophageal temperature recovery time

The following study examined the effect of 15° head-down tilt (HDT) on postexercise heat loss and hemodynamic responses. We tested the hypothesis that recovery from dynamic exercise in the HDT position would attenuate the reduction in the heat loss responses of cutaneous vascular conductance (CVC) and sweating relative to upright seated (URS) recovery in association with an augmented hemodynamic response and an increased rate of core temperature decay. Seven male subjects performed the following three experimental protocols: 1) 60 min in the URS posture followed by 60 min in the 15° HDT position; 2) 15 min of cycle ergometry at 75% of their predetermined V̇O_{2 peak} followed by 60 min of recovery in the URS posture; or 3) 15 min of cycle ergometry at 75% of their predetermined V̇O_{2 peak} followed by 60 min of recovery in the 15° HDT position. Mean skin temperature, esophageal temperature (T _es), skin blood flow, sweat rate, cardiac output (CO), stroke volume (SV), heart rate (HR), total peripheral resistance, and mean arterial pressure (MAP) were recorded at baseline, end exercise, 2, 5, 8, 12, 15, and 20 min, and every 5 min until end of recovery (60 min). Without preceding exercise, HDT decreased HR and increased SV (P ≤ 0.05). During recovery after exercise, a significantly greater MAP, SV, CVC, and sweat rate and a significantly lower HR were found with HDT compared with URS posture (P ≤ 0.05). Subsequently, a significantly lower T_es was observed with HDT after 15 min of recovery onward (P ≤ 0.05). At the end of 60 min of recovery, T_es remained significantly elevated above baseline with URS (P ≤ 0.05); however, T_es returned to baseline with HDT. In conclusion, extended recovery from dynamic exercise in the 15° HDT position attenuates the reduction in CVC and sweating, thereby significantly increasing the rate of T_es decay compared with recovery in the URS posture.