Quantitative measurement of sweating rate is a useful indicator of the state of autonomic nerves and related factors such as stress response or body temperature regulation. Specifically, it is known that mental stress increases mental sweating, and deep body temperature and dehydration increase thermal sweating. Therefore, continuous sweat measurement with a small sweating rate meter is expected to be useful for the management of mental stress as well as the prevention of heat stroke. In this study, two small sweating rate meters, one having high resolution and the other having a large dynamic range, were developed and used to measure mental sweating and thermal sweating. These devices determine the sweating rate by the conventional method, which measures the humidity difference between ambient air and air moistened by sweat. Measurement resolution and dynamic range can be adjusted by controlling the air flow rate. The device for measuring mental sweating rate consists of a main body, which has an air pump and two humidity sensors, and a capsule connected to the main body by tubes in which air flows. The device for measuring thermal sweating rate has a pump and two humidity sensors, an aperture instead of a capsule, and a flow channel on a flexible substrate. The mental sweating rates during arithmetic and speech tasks were measured on the plantar aspect of the big toe using the mental sweating rate meter. The present study on part of the sole showed two sweating types ; a reaction type and a low-reaction type. During the mental stress tasks, sweating rate increased by 0.43 mg/min/cm2 compared to that at rest in reaction type subjects, but by less than 0.1 mg/min/cm2 in low-reaction type subjects, showing very low responses to stimulations. The thermal sweating rate during immersion of the lower legs in warm water was measured using the thermal sweating meter worn on the forearm. Sweating rate increased by approximately 0.4 mg/min/cm2 on average due to thermal stress, and was also successfully measured. These results show that the small sweating rate meters developed in this study can be used for measuring mental and thermal sweating rates.
