TEWL, Closed-Chamber Methods: AquaFlux and VapoMeter
TransEpidermal water loss (TEWL) is recognised as the main indicator of skin barrier function. Since the 1970s, the open-chamber method of measurement has established itself as the main method for TEWL measurement and a de facto standard against which newer technologies are judged. However, the open-chamber method is known to suffer from a number of limitations, the main one being disturbance by ambient air movements. This limitation can be overcome by closing the measurement chamber, but this design change affects other aspects of the measurement.
Closed-chamber instruments bring a new dimension to TEWL measurement, because their immunity to disturbance by external air movements makes it possible for such measurements to migrate away from the well-controlled laboratory environment into the workplace or clinic. This and other aspects of their design liberate them from many of the restrictions and precautions recommended in the now outdated TEWL guidelines.
This chapter describes two commercial closed-chamber instruments, the AquaFlux and the VapoMeter, whose characteristics are discussed within the context of the established open-chamber method. These instruments differ in measurement principle, concept and design. The AquaFlux, which uses the condenser-chamber method of measurement, is a benchtop, mains-powered instrument. The VapoMeter, which uses the unventilated-chamber method of measurement, is a self-contained, battery-powered instrument. Their performance characteristics are also quite different, with accuracy, sensitivity and repeatability the main features of the AquaFlux and speed and mobility the main features of the VapoMeter.
KeywordsMeasurement Chamber Water Vapour Flux Skin Barrier Function Sweat Gland Activity TEWL Measurement
We thank Markus Steiner of Aberdeen University, Scotland, for providing the raw Tewameter-VapoMeter comparison data used in Fig. 31.3 and Jouni Nuutinen of Delfin Technologies Ltd, Finland, for providing unpublished VapoMeter angular response data.
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