Usefulness of R-R interval and its variability in evaluation of thermal comfort

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Abstract
The use of R-R interval and the coefficient of variation in R-R intervals (CVR-R) for the evaluation of thermal comfort was investigated. The experiments were carried out with ten male subjects but data from one were excluded from the analysis. Thermal sensation, comfort, and tolerance of environmental conditions were reported and mean skin temperature, R-R interval and CVR-R were monitored during a 3 h period in a climatic chamber with the operative temperature set at 26, 20, or 30° C. Relative humidity was maintained at ca. 50% in each case. At the operative temperature of 20° C, the mean skin temperature was significantly lower, the cold sensation was significantly more intense, and discomfort was significantly greater than at 26° C and R-R interval was increased significantly. Seven of the nine subjects were unable to tolerate this thermal environment. The R-R interval and CVR-R were increased in five and four of those seven subjects, respectively. At the operative temperature of 30° C, the mean skin temperature was significantly higher, and the sensation of warmth was significantly more intense than at 26° C. Seven of the nine subjects felt discomfort, and four of the seven reported an inability to tolerate this thermal environment. The R-R interval and CVR-R were decreased in four and three of these four subjects, respectively. At the operative temperature of 20° C CVR-R was significantly greater than that at 30° C. Together with the subjective indices, R-R interval and CVR-R are considered worthy of further evaluation as objective indications of the effect on people of the thermal environment.