Firefighter pre-frontal cortex oxygenation and hemodynamics during rapid heat stress

[Display omitted] •This study demonstrated that rapid heat stress causes cerebral oxygenation and hemodynamic changes.•This study demonstrated that Tc 38 °C is associated with a peak, plateau, and subsequent decrease in cerebral oxygenation and hemodynamics.•This study demonstrated a difference in u...

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Published in:Brain research 2023-01, Vol.1798, p.148156-148156, Article 148156
Main Authors: Coehoorn, Cory J., Patrick Neary, J., Krigolson, Olave E., Stuart-Hill, Lynneth A.
Format: Article
Language:English
Subjects:
Fatigue
Firefighters
Firefighting
Haemodynamics
Heat Stress
Heat-Shock Response
Hemodynamics - physiology
Hemoglobins - metabolism
Humans
Hyperthermia
Male
Oxygen
Oxygen Consumption
Oxygenation
Oxyhemoglobins - metabolism
Prefrontal Cortex - metabolism
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Summary:[Display omitted] •This study demonstrated that rapid heat stress causes cerebral oxygenation and hemodynamic changes.•This study demonstrated that Tc 38 °C is associated with a peak, plateau, and subsequent decrease in cerebral oxygenation and hemodynamics.•This study demonstrated a difference in unilateral prefrontal cortex activation when exercising in the heat while wearing personal protective equipment. This study evaluated the impact of rapid heat stress on prefrontal cortex (PFC) oxygenation and hemodynamics. Previous work has demonstrated that heat stress affects cerebral oxygenation and hemodynamics. Fourteen male subjects performed a graded exercise test to a termination criterion (volitional maximum, core temperature = 39.5 °C, or a 2-hour time cap) with (GEAR) and without (NOGEAR) firefighting gear in a laboratory with an ambient temperature of 25–26 °C. Changes in oxyhemoglobin (O2Hb), total hemoglobin (tHb), and tissue oxygen saturation index (TSI %) were monitored in the left and right PFC using near-infrared spectroscopy (NIRS). Significant NIRS results were a plateau in the left-side O2Hb and tHb at 80 % of the time to termination (TTT) in NOGEAR, and 60 % of TTT in GEAR. These TTT points were when the subject's core temperature (Tc) was equal to 38 °C. Additionally, there was higher left-side PFC activation during GEAR, as indicated by a significant decrease in TSI % from start to end of exercise and double the reduction in TSI % per minute in PPE compared to NOGEAR. There were no significant differences during the NOGEAR session. These data suggest that a rapid heat stress scenario (GEAR) causes altered cerebral oxygenation and hemodynamic response in the left-side PFC. The left PFC could be working harder to prevent fatigue in GEAR. This could affect cognitive processes during or following exercise in the heat while wearing personal protective equipment. Our results also support previous research demonstrating that NIRS is a sensitive metric of fatigue.
ISSN:0006-8993
1872-6240
DOI:10.1016/j.brainres.2022.148156