Thermal Response Patterns Provide Early Sign of Exertional Heat Stroke during Intense Activity

Area of Science:

• Physiology
• Environmental Health
• Military Medicine

Background:

• Exertional Heat Stroke (EHS) poses a significant risk to active populations, with severe cases leading to organ damage or death.
• Early detection of EHS is crucial for timely intervention but is challenging due to its rarity in human studies.
• Physiological monitoring offers a potential method for early warning of EHS risk.

Purpose of the Study:

• To compare physiological response patterns, including heart rate and thermal data, between individuals who experienced EHS and matched controls during a military ruck march.
• To identify distinct physiological signatures associated with EHS during strenuous physical activity.

Main Methods:

• Collected physiological data (heart rate, skin temperature, core temperature, accelerometry) using chest-mounted monitors on seven EHS cases and 21 matched controls during a loaded military ruck march.
• Analyzed mean heart rate (HR), skin temperature (Tsk), estimated core temperature (Tect), and Gait Instability Index (GINI) across four quartiles of the event.
• Utilized Two-way ANOVA to compare physiological profiles between the EHS and control groups.

Main Results:

• Estimated core temperature (Tect) increased significantly faster over time in the EHS group (p=0.001).
• Heart rate (HR) and skin temperature (Tsk) exhibited different patterns and were elevated in the EHS group during later quartiles, narrowing the Tsk-Tc gradient.
• The Gait Instability Index (GINI) was higher in the EHS group only in the final quartile.

Conclusions:

• This study presents a novel early detection method for EHS in prolonged military exercises.
• The method integrates patterns of heart rate, skin temperature, and estimated core temperature for risk identification.
• This approach has the potential to enhance safety during demanding physical activities in military and other active communities.