Development and testing of a perspiration measuring system
Introduction
There are two types of perspiration for human beings. The first type is insensible perspiration where water is lost from the skin or through vapour exchange from lungs. The second type is called active sweating. Physiological stress, such as heat, mental stimuli and exercise, could induce the activity of sweating. The thermal sweating is an important reaction for to be the thermostat of the human body.
Two types of disorder for human sweating are found in clinical diagnosis. Excessive sweating is called hyperhidrosis and the lack of sweating is hypohidrosis. So the amount of sweat or the sweat rate of a human being could serve as the indexes for a physician to classify a patient's conditions.
A basic and simple method for detecting the amount of sweating is to use the colorimetric method [1], [2]. The solutions consist of iodine, castor oil and diluted alcohol sprayed over the test sites of human skin. As the sweat generates, the color of solution would change. This method is simple and could serve as the indication of some disease [3]. However, if the test subject was uncomfortable then the sweating phenomenon could not be recorded quantitatively.
Ventilated chambers have been used by many researchers. A ventilation chamber covering the human skin and the evaporative water loss would then be detected by a different technique. An electrohygrometer was applied to measure the water loss [4], [5], [6], [7]. Brengelmann et al. [9] selected the dew-point meter to measure the sweating rate.
Ohhashi et al. [6] modified the ventilated chamber methods. The inlet air of chambers was conditioned. The dehumidified air was passed through a cylinder filled with silica gel for dehydration. The increase of water vapour from human skin was detected with a Vaisala capacitive humidity sensor. Only one sensor is required to measure the humidity of outlet gas. Birklein et al. [8] modified this method and used it to observe that the sudomotor function. The inlet air was replaced by the dry nitrogen gas. The relative humidity of outlet air was measured with hygrometer.
In spite of the popularity of the ventilation chamber methods, the performance evaluation of these measuring systems was lacking. The airflow rate for the ventilation chamber was very important. If the air velocity was too high, the epidermis would be dried out and consequently there would be a fall in the water loss rate. If the air velocity was too low, the relative humidity would be too high, and the water vapour could be condensed in the ventilated tubes.
Smallwood and Thomas [10] mentioned that the error sources for the evaporative water loss from the ventilation chamber were caused by the measurement errors in air temperature, relative humidity, saturated vapour pressure estimation and gas flow rate measurement. The estimated accuracy was about 10% of the reading of their devices.
Recently, the performance of sensors has been improved significantly. The calibration technique and traceable system of sensors are popular in the research field [11]. This information could be applied to observe the performance of perspiration measurement system.
The purpose of this study was to develop a convenient ventilation chamber to serve as the device for perspiration measurement. The temperature and relative humidity sensors were calibrated and the calibration equations were developed to improve the accuracy. Two indexes were proposed to validate the measured performance of this device.
Section snippets
Experimental devices
The relative humidity sensor adopter in this study was a Shinyei THT-B121 resistive-type transmitter (Shinyei Kaisha Co., Tokyo, Japan). The measuring range according to manufacturer's specifications was from 20% to 95% RH. The sensing element was a Macro-molecule element.
The type-K thermocouple wires (Omega Engineering, USA) were applied to measure the temperature.
The airflow velocity was detected by a Top-Trak 822S flow meter (Sierra Instruments, USA). The measuring range was from 0 to 1.0 m3
Sweating curves
The typical curve for the quantity of perspiration of a human being after exercising is shown in Fig. 5. As the test subject finished exercising, and we began to detect perspiration, the quantity of perspiration increased rapidly due to the increase of body temperature. The quantity of perspiration was increased to the maximum values. This period is called acceleration stage (symbol as A in Fig. 5). In the measuring period, the human body was kept at rest and the body temperature was decreased
Conclusions
Sweating measurement is a very useful tool for the physiological health state of the human body. In this study, a ventilated chamber was designed to serve as the measuring device. The temperature and relative humidity sensors were calibrated to ensure the accuracy of its performance. The results of sweating curves at three physiological states validate the reasonableness and usefulness of this device. The sweating quantity of the three states did not have a significant relationship with the BMI
Conflict of interest statement
None of the authors have been any financial or personal relationships with people or organizations that could inappropriately influence our work.
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