Physiological responses to repeated heat exposure under equal work load conditions

Objectives. This study aimed to verify the responses of skin temperature, oxygen saturation, blood pressure, rate pressure product (RPP), heart rate (HR) and HR variability after continuous and intermittent exposure to heat from a fire, keeping the work load equal between the conditions. Methods. Sixteen men from a fire department were subjected to two experimental conditions: continuous exposure to the heat from a fire for 30 uninterrupted minutes (1 × 30 min); and intermittent exposure to the heat of the fire organized by two 15-min re-entries of exposure to the heat interspersed with 10 min of non-exposure (2 × 15 min). Results. The main finding was lower percentage changes in HR (+1.7% vs +38% vs +26%), mean normal interval (-0.97% vs -26% vs -20%), RMSSD (-5.0% vs -62% vs -48%) and RPP (+0.79% vs +38% vs 34%) in re-exposure (15-30 min) when compared for 0-30 min and 0-15 min, respectively. Conclusion. Under equal workloads, intermittent exposure to heat is an efficient strategy for fire suppression activities. In addition to skin temperature and HR, RPP constitutes another variable to monitor firefighter health between re-entries, as it is easy to administer, inexpensive and reflects cardiac overload.