Development and testing of a perspiration measuring system

https://doi.org/10.1016/j.medengphy.2010.01.007Get rights and content

Abstract

Sweating measurement is a very useful tool for the physiological health state of the human body. A sweating measuring system developed in this study was composed of several sensors. All sensors were calibrated to ensure the accuracy. Three pretreatment physiological states for test subjects before sweating measurement included sit and rest for 5 min, walking for 5 min, and running for 5 min. The whole sweating value was measured and calculated over 5-min periods. The results of sweating measurement indicated the usefulness of this device. The sweating quantity of three states did not have a significant relationship with the height, weight and body mass index (BMI) values of subjects. The first sweating index is the difference between active treatment and sitting state. The second sweating index is the ratio between active state and sitting. The relationship between two sweating index and BMI values could be found. This device could serve as a detecting tool to establish the sweating database for normal conditions and to be used for diagnosis.

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.

References (15)

  • K.T. Sato et al.

    One step iodine starch method for direct visualisation of sweating

    Am. J. Med. Sci.

    (1988)
  • F.R. Birklein et al.

    Sudomotor function in sympathetic reflex dystrophy

    Pain

    (1997)
  • A.K.M. Shamsuddin et al.

    Continuous monitoring of single-sweat-gland activity

    Physiol. Meas.

    (2001)
  • M.N. Kanai et al.

    Acetylcholine-Induced activation of the eccrine sweat glands in a case of hypohidrotic congenital ectodermal dysplasia

    J. Electron Microsc.

    (1989)
  • G.E. Nilsson

    Measurement of water exchange through skin

    Med. Biol. Eng. Comput.

    (1977)
  • T. Ohhashi

    An apparatus for continuous recording of sweating rate by use of a hygrometer of electrostatic capacity type and its medical application from the autonomic nervous system points of view

    Bull. Phys. Fit. Res. Inst.

    (1987)
  • T. Ohhashi et al.

    Human perspiration measurement

    Physiol. Meas.

    (1998)
There are more references available in the full text version of this article.

Cited by (9)

  • Portable sweat rate sensors integrated with air ventilation actuators

    2016, Sensors and Actuators, B: Chemical
    Citation Excerpt :

    There are two types of forced ventilation methods: pump-based types and ice condenser-based types. The pump-based types [16,17] measure the humidity difference between the inlet and the outlet of the humidity chamber during the forced ventilation of the chamber by pump, allowing continuous sweat rate measurement. However, the pump-based types have bulky size due to external pumps and pneumatic lines, thus it has a limit to monitoring applications.

  • Comparison of GUM and Monte Carlo methods for evaluating measurement uncertainty of perspiration measurement systems

    2016, Measurement: Journal of the International Measurement Confederation
    Citation Excerpt :

    Ventilated chambers are often used to measure sweat rate. The human skin is covered by a special chamber and the evaporative vapor from skin is measured by different methods [21–23]. Smallwood and Thomas noted sources of error with using of a ventilation chamber [22].

  • Multiphysics Modeling of a Wearable Sensor for Sweat Rate Measurements

    2020, 2020 IEEE International Workshop on Metrology for Industry 4.0 and IoT, MetroInd 4.0 and IoT 2020 - Proceedings
View all citing articles on Scopus
View full text