Carbohydrate Ingestion Attenuates Cognitive Dysfunction Following Long-Duration Passive Heat Stress In Humans

Abstract

PURPOSE: To determine if electrolyte or carbohydrate supplementation would reduce cognitive dysfunction in humans following long-duration passive heat stress. METHODS: Fifteen subjects performed 2 visits of 120 minutes of passive heat stress wearing liquid perfused suits infused with 50 °C water. In random order, subjects consumed fluids supplemented with electrolytes (E) or electrolytes+carbohydrates (E + C). Pre- and post-heat stress, body mass (BM) and plasma osmolality (pOsm) were measured. Heat rate, blood pressure, Physiological Strain Index (PSI), core temperature (TC), plasma glucose, plasma lactate, respiration rate, end-tidal CO2, internal carotid artery (ICA) velocity, and ICA diameter were recorded every 15 minutes. Cognitive function was assessed via the Automated Neurophysiological Assessment Metric (simple vs. complex cognitive tasks) at 30 minutes and at 120 minutes. RESULTS: There were no significant differences between fluid conditions (E & E + C) for BM loss (0.33 ± 0.2 & 0.22 ± 0.2 kg), pOsm (Δ3.6 ± 8.0 & 5.9 ± 6.7 mmol/L), peak-PSI (6.2 ± 0.3 & 5.9 ± 0.3), peak TC (38.9 ± 0.1 & 38.9 ± 0.1 °C), and ICA diameter (0.42 ± 0.01 & 0.42 ± 0.01 cm). Plasma glucose was significantly higher in the E + C condition at 60, 75, 90, 105, & 120 minutes (P < 0.05). No significant differences were noted between the 2 fluid conditions for the simple cognitive tasks however, in both fluid conditions, cognitive function was impaired following the bout of passive heat stress. Interestingly, compared to the E condition, the E + C condition demonstrated improved performance on all complex cognitive tasks (P < 0.05). Furthermore, compared to the E condition, the E + C condition demonstrated a significant increase in ICA blood velocity, blood flow, and vascular conductance at 90, 105, and 120 minute time points (P < 0.05) and a significant decrease in mean arterial pressure and heart rate at 60, 75, 90, 105, and 120 minute time points (P < 0.05). CONCLUSIONS: These data are the first to suggest that exogenous glucose administration may have a protective effect on cognitive function during long-duration passive heat stress. Furthermore, this protection is associated with elevated global cerebral blood flow and glucose delivery to the brain.