Quantitative Evaluation of an Unrestrictive Sweat Rate Measurement Device

Shin-ichiro Seno , Tetsu Nemoto , Masakazu Fukuoka , Atsushi Watanabe , Sachiko Kato , Eiki Kogure , Hiroko Kobayashi , Hideaki Shimazu
Vol. 5 (2016) p. 76-82

Sweating, the intermittent secretion of fluid from the sweat glands, is an indispensable mechanism for the regulation of body temperature. The methods used to measure the sweat rate include an iodine starch test, a weight assay, and an ion electric conductivity method. The ventilation capsule method is another method for quantification of sweat rate. However, this method has a problem in that the subject’s physical activity is restricted by the firmly attached measurement probes. SNT-200, a wearable sweat meter developed by Rousette Strategy Inc., is already commercially available. This sweat meter contains silica gel that serves as an absorbent for sudoriferous steam and uses a temperature–humidity sensor to detect humidity changes in the device caused by sweating. However, the accuracy of the measurement has not yet been sufficiently investigated. This study was designed to provide evidence to validate the underlying measurement principle and accuracy of the device. We simulated various sweating conditions and performed simulated sweating measurements using SNT-200. In the first experiment, continuous sweating over a wide body surface was simulated. The calculated absorbed steam volume was 1.84 times greater than the real transpiration rate. In the second experiment, sweating was simulated in the form of water drops, and the sweat meter absorbed the generated steam. In the second experiment, the data obtained using SNT-200 was in good accord with the volume dispensed by a micropipette. These experiments provided convincing evidence that the total area of four steam holes (A1, in the equation for calculating the sweat rate) required correction. We therefore modeled the effective absorption area of the sweat meter as one circle encompassing the four holes (8 mm in diameter; 52 mm2) instead of a summation of the areas of four steam holes. Defining the effective absorption area by this method modified the value calculated in the first experiment, which agreed with the transpiration rate. In addition, the modified moisture absorption volume in the sweat meter converged within ± 20% error of the actual measurement, except at 30℃.