Continuous monitoring of sweating by electrical conductivity measurement.

A method of continuous monitoring of sweating was developed in which sweat was detected by changes in the conductivity of perfusing water. An ion-free solution was perfused at a constant flow rate through a chamber attached to the skin surface. The chamber was designed so that the electrodes were installed inside at the inlet and outlet, and a 14 mm3 channel was constructed at the bottom to wash out sweat. The 90% response time was 0.12 s. Attaching the chamber to the palm allowed measurements to be made with the subject seated in a comfortable environment. The sweat rate and heart rate were measured simultaneously with an air-ventilation chamber and a heart rate counter, respectively, with the subjects at rest, and under stresses such as grasping hands and doing mental arithmetic. This method yields sweat responses similar to those obtained with an air-ventilation chamber and simultaneous heart rate measurements. The main advantages of this method are faster response time and smaller observation area.