Comparison of closed chamber and open chamber evaporimetry

Abstract

Recently it has been asserted that a closed chamber evaporimeter, the VapoMeter, offers advantages over standard open chamber devices in measuring transepidermal water loss (TEWL). Purported improvements include the ability to take measurements at any angle, short reading times and insensitivity to external air currents. These claims are compelling, considering that measuring TEWL at diverse skin sites can be tedious, especially with children. The primary aim of this study was to compare the performance of closed and open chamber instruments when they were held at various angles and, secondly to evaluate the ability of the devices to discriminate between test conditions. The performance of closed chamber (VapoMeter) and open chamber (DermaLab) evaporimeters were compared by measuring water vapor emitted from IMS Vitro-skin that had been hydrated to a predetermined level. Measurements were taken at three angles from vertical - 0 degrees, 45 degrees, and 90 degrees. Vitro-skin samples were weighed periodically throughout the experimental phase to verify water loss rates. Both the VapoMeter and the DermaLab yielded significantly lower water loss values when held at angles that varied from the vertical (0 degrees) position, indicating that the closed chamber device is no more capable of accurately measuring TEWL at any angle than an open chamber instrument. The DermaLab provided better discrimination than the VapoMeter when the instruments were held vertically, as is the only prescribed testing position for open-chamber instruments. The VapoMeter was easier to use than the DermaLab; however, there was evidence that the sealed chamber could become saturated under high water loss conditions. Previous assertions that the VapoMeter closed chamber evaporimeter is capable of measuring TEWL regardless of angle were not validated. Each device appeared capable of accurately estimating water loss rates only in the vertical position. Although the VapoMeter was easier to use than the open chamber device, its tendency to become saturated under high water loss conditions could be a disadvantage when assessing dynamic TEWL.