Aural canal, esophageal, and rectal temperatures during exertional heat stress and the subsequent recovery period

Abstract

Context: The measurement of body temperature is crucial for the initial diagnosis of exertional heat injury and for monitoring purposes during a subsequent treatment strategy. However, little information is available about how different measurements of body temperature respond during and after exertional heat stress.

Objective: To present the temporal responses of aural canal (T(ac)), esophageal (T(es)), and rectal (T(re)) temperatures during 2 different scenarios (S1, S2) involving exertional heat stress and a subsequent recovery period.

Design: Randomized controlled trial.

Setting: University research laboratory.

Patients or other participants: Twenty-four healthy volunteers, with 12 (5 men, 7 women) participating in S1 and 12 (7 men, 5 women) participating in S2.

Intervention(s): The participants exercised in the heat (42 degrees C, 30% relative humidity) until they reached a 39.5 degrees C cut-off criterion, which was determined by T(re) in S1 and by T(es) in S2. As such, participants attained different levels of hyperthermia (as determined by T(re)) at the end of exercise. Participants in S1 were subsequently immersed in cold water (2 degrees C) until T(re) reached 37.5 degrees C, and participants in S2 recovered in a temperate environment (30 degrees C, 30% relative humidity) for 60 minutes.

Main outcome measure(s): We measured T(ac), T(es), and T(re) throughout both scenarios.

Results: The T(es) (S1 = 40.19 +/- 0.41 degrees C, S2 = 39.50 +/- 0.02 degrees C) was higher at the end of exercise compared with both T(ac) (S1 = 39.74 +/- 0.42 degrees C, S2 = 38.89 +/- 0.32 degrees C) and T(re) (S1 = 39.41 +/- 0.04 degrees C, S2 = 38.74 +/- 0.28 degrees C) (for both comparisons in each scenario, P < .001). Conversely, T(es) (S1 = 36.26 +/- 0.74 degrees C, S2 = 37.36 +/- 0.34 degrees C) and T(ac) (S1 = 36.48 +/- 1.07 degrees C, S2 = 36.97 +/- 0.38 degrees C) were lower compared with T(re) (S1 = 37.54 +/- 0.04 degrees C, S2 = 37.78 +/- 0.31 degrees C) at the end of both scenarios (for both comparisons in each scenario, P < .001).

Conclusions: We found that T(ac), T(es), and T(re) presented different temporal responses during and after both scenarios of exertional heat stress and a subsequent recovery period. Although these results may not have direct practical implications in the field monitoring and treatment of individuals with exertional heat injury, they do quantify the extent to which these body temperature measurements differ in such scenarios.

Figure 1

Esophageal, aural canal, and rectal temperatures during exertional heat stress and throughout the subsequent period of cold-water immersion in scenario 1. Values are mean ± standard error for 12 participants. ^a Indicates different from aural canal temperature (P < .05). ^b Indicates different from rectal temperature (P < .05). The vertical dashed lines delimit each period. The horizonal dashed line represents the mean of all 3 resting core temperatures.

Figure 2

Differences between esophageal and rectal temperatures as a function of percentage of total exercise time during exertional heat stress as defined by A, an esophageal temperature of 39.5°C or B, a rectal temperature of 39.5°C. Values are mean ± standard error for 12 participants. ^a Indicates different from 20% of total exercise time (P < .05).

Figure 3

Esophageal, aural canal, and rectal temperatures during exertional heat stress and throughout the subsequent inactive recovery in scenario 2. Values are mean ± standard error for 12 participants. ^a Indicates different from rectal temperature (P < .05). ^b Indicates different from aural canal temperature (P < .05). The vertical dashed lines delimit each period. The horizonal dashed line represents the mean of all 3 resting core temperatures.