A Sweat Sensor for Qualitative Measurements

To study objectively the sweat response during motion sickness, a need existed for a small sweat-sensing device with a short latency of response, a fast response time, and the ability to follow the time course of the sweat response. The design and function of a sweat-sensing device for continuous monitoring of the sweat response are described. A lithium chloride-aluminum chloride sensing element, which changes resistance depending on the uptake or release of moisture, is used in this sensor. The sensing element is enclosed in a housing that is designed to circulate air from the skin surface to the sensing element. Air is supplied from a compressed-air cylinder and is controlled with a needle valve flowmeter assembly. With an air-flow rate of 15 ccmin and in response to a step change in moisture content on the skin surface, the sensor has a latency of 1.5 seconds and a rise time to reach 90 percent of the saturation level of about 28 seconds. A major disadvantage of the sensor is that with heavy sweat rates, the sensing element saturates, resulting in relatively long drying out times. This can be partially offset by using higher air-flow rates, but at the expense of reduced sensitivity. The application of this sensor has shown that it is capable of responding to the cyclic sweat activity commonly seen when skin-resistance measurement techniques are used to monitor the sweat response. Author