Combined Heat and Mental Stress Alters Neurovascular Control in Humans

Abstract

This study examined the effect of combined heat and mental stress on neurovascular control. We hypothesized that muscle sympathetic nerve activity (MSNA) and forearm vascular conductance (FVC) responses to mental stress (MS) would be augmented during heat stress (HS). Twelve subjects performed 5 min of MS during normothermia (NT: Tcore; 37 ± 0 °C) and HS (38 ± 0 °C). Heart rate (HR), mean arterial pressure (MAP), MSNA, forearm skin vascular conductance (SkVCf), and FVC were recorded. HS increased HR, MSNA, SkVCf, and FVC at rest, but did not change MAP. MS increased MAP during both conditions, but increases during HS (Δ10 ± 2 mmHg) were blunted compared to NT (Δ15 ± 1 mmHg; interaction, P<0.01). MS increased total MSNA during both conditions, but increases during HS were greater (Δ4668 ± 1224 units) relative to NT (Δ1267 ± 558 units; interaction, P<0.01). MS decreased SkVCf during HS (Δ−19 ± 5 units; P<0.001), but not during NT (Δ−1 ± 0 units). MS elicited similar increases in MSNA burst frequency, HR, and FVC during both conditions. In conclusion, these findings indicate that MS elicits a blunted increase of MAP during HS, despite greater increases in total MSNA and cutaneous vasoconstriction. These findings could be of particular interest to those exposed to mentally demanding tasks in hyperthermic environmental conditions (i.e. soldiers, firefighters, and athletes). Supported by APS and NIH.