Quantitative Evaluation of an Unrestrictive Sweat Rate Measurement Device

Quantitative evaluation of skin barrier function using water evaporation time related to transepidermal water loss

BACKGROUND

Transepidermal water loss (TEWL) is often used as an index for skin barrier function. The skin barrier tester, SBT-100 (Rousette Strategy Inc), measures the TEWL, water evaporation time, and time constant by contacting the skin and diffusing water into the closing measurement chamber. However, the relationship between the TEWL and time constant has not been sufficiently investigated. This study involved analyzing the underlying measurement principle and obtaining data through two experiments.

MATERIALS AND METHODS

The TEWL and time constant were measured using SBT-100. Experiment 1 produced a simple simulation model for continuous water evaporation from the skin using a moisture-permeable film. In experiment 2, four skin sites of 43 healthy volunteers were examined from May to September 2018.

RESULTS

In experiment 1, the TEWL increased and time constant decreased, following an increase in humidity in the external environment. Both parameters demonstrated significant negative correlation (drying: ρ = -0.832, p < 0.001). For the 43 healthy volunteers who participated in experiment 2, their TEWL increased and time constant decreased in summer. For all skin measurement sites, both data demonstrated significant negative correlation (forehead: ρ = -0.909, p < 0.001; back of the left hand: ρ = -0.829, p < 0.001; left lateral elbow: ρ = -0.896, p < 0.001; left lateral malleolus: ρ = -0.865, p < 0.001).

CONCLUSION

Results indicated that the time constant is significantly correlated with TEWL. Furthermore, the time constant can be used as a parameter for evaluating skin barrier function.

Conductive Thread-Based Textile Sensor for Continuous Perspiration Level Monitoring

Individual perspiration level indicates a person’s physical status as well as their comfort level. Therefore, continuous perspiration level measurement enables people to monitor these conditions for applications including fitness assessment, athlete physical status monitoring, and patient/elderly care. Prior work on perspiration (sweat) sensing required the user either to be static or to wear the adhesive sensor directly on the skin, which limits users’ mobility and comfort. In this paper, we present a novel conductive thread-based textile sensor that measures an individual’s on-cloth sweat quantity. The sensor consists of three conductive threads. Each conductive thread is surrounded by a braided cotton cover. An additional braided cotton cover is placed outside the three conductive threads, holding them in a position that is stable for measurement. the sensor can be embedded at various locations on a person’s clothing. When the person sweats, the cotton braids absorb the sweat and change the conductivity (resistance) between conductive threads. We used a voltage dividing circuit to measure this resistance as the sensor output (DC). We then conducted a sensor calibration to map this measured voltage to the quantity of electrolyte solution (with the same density as sweat) applied to the sensor. We used this sensor to measure individuals’ perspiration quantity and infer their perceived perspiration levels. The system is able to limit the average prediction error to 0.4 levels when compared to five pre-defined perceived perspiration levels.