Regional Variations in the Reliability of Local Sweat Rate Measured via the Ventilated Capsule Technique during Whole‐body Passive Heating

Abstract

The ventilated capsule technique uses hygrometry to measure time‐dependent changes in sweating over small areas (~1–5 cm2) on the body surface. Despite the widespread use of this technique, evaluations of its reliability (i.e., consistency) are sparse and have been restricted to a single region (forearm) during exercise‐heat stress. This presents a critical knowledge gap, as the reliability of this technique may be region‐specific due to inter‐regional variation in sweat rate. Further, understanding regional variations in the reliability of this technique has important practical utility for experimental design, statistical analysis, and sample size estimates. We therefore assessed the reliability of local sweating across various body regions during exposure to increasing levels of whole‐body heat stress. Sweat rate was measured using ventilated capsules (3.5 cm2) at 9 locations (i.e., forehead, chest, abdomen, bicep, forearm, hand, quadriceps, calf, and foot) in twelve young men (age: 25 [SD 5] years). On three occasions, a whole‐body water perfused suit was used to raise and clamp esophageal temperature at three levels of hyperthermia: 1) +0.7 ± 0.1°C above baseline (low‐heat stress; LHS); 2) +1.3 ± 0.1°C (moderate‐heat stress; MHS); and 3) +1.8 ± 0.1°C (high‐heat stress; HHS). An average of the data collected in the final 5‐min of each heating stage (stable sweating) was used for analysis. Reliability was assessed using the interclass correlation coefficient (ICC; an index of measurement consistency), with values ≥0.7 considered suitable for research purposes. At LHS, average sweat rate across the 9 regions was 1.01 mg·min−1·cm−2, ranging from 0.85 to 1.28 mg·min−1·cm−2 (foot and chest, respectively). The average ICC across regions was 0.66, ranging from 0.35 to 0.94 (forehead and chest, respectively). Of the 9 regions, abdomen (0.94), calf (0.81), forearm (0.79), quadriceps (0.78) and chest (0.74) exceeded the 0.7 ICC threshold. In the MHS condition, average sweat rate across all sites was 1.21 mg·min−1·cm−2, ranging from 0.91 to 1.53 mg·min−1·cm−2 (bicep and chest, respectively). The average ICC across regions was 0.60, ranging from 0.15 to 0.88 (hand and abdomen, respectively). Of the 9 regions, abdomen (0.88), quadriceps (0.79) and forearm (0.77) exceeded the 0.7 ICC threshold. In the HHS condition, average sweat rate across all sites was 1.28 mg·min−1·cm−2, ranging from 1.02 to 1.62 mg·min−1·cm−2 (quadriceps and chest, respectively). The average ICC across regions was 0.59, ranging from 0.21 to 0.86 (hand and abdomen, respectively). Of the 9 regions, abdomen (0.86), quadriceps (0.77) and calf (0.73) exceeded the 0.7 ICC threshold. Our findings indicate that the region and level of hyperthermia will impact the consistency of local sweat rates measured with the ventilated capsule technique and therefore the likelihood of detecting an effect of an intervention/comparison if one exists.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada.