Transepidermal water loss kinetic modeling approach for the parameterization of skin water dynamics

Abstract

Background/aims: The evaluation of transepidermal water loss (TEWL) is one of the methods most frequently used in studies involving skin water dynamics. However, TEWL does not provide a direct measurement of epidermal barrier function, being rather a surrogate effect of it. In particular, when external stimuli change cutaneous water balance, these stimuli must be taken into account in order to achieve a rigorous interpretation of the results. Since TEWL is primarily attributed to the water flux from the deepest layers of the skin, through the epidermis, and towards the external environment, this whole process is reasonably compliant with Fick's first law of diffusion. Within this perspective, the aim of this work was to develop a two compartment mathematical model capable of quantitatively describing cutaneous water mass balance over time and thus to provide practical and objective comparable parameters that are particularly useful for studies critically depending on a precise evaluation of TEWL. Methods: The theoretical basis for the proposed model was tested with data collected from different protocols that use TEWL as the main indicator of induced cutaneous alterations. Those alterations involved either external inputs or intrinsic changes on the cutaneous pathway capable of changing the whole water balance across the skin, either altering epidermal cohesion or promoting a significant influx of external water. Results: Both the evaporation and the hydration equilibrium processes, merged within the TEWL curve profiles, were thoroughly described in a quantitative fashion using a mathematical model. Direct parameters were calculated, such as kinetic rate constants (khydr and kevap) and half‐life times (t1/2 hydr and t1/2 evap) chosen to describe the hydration and evaporation processes. Secondary parameters, such as time to reach the maximum and an area under the curve derived parameter, the dynamic water mass (DWM), were also calculated, providing additional data particularly useful for comparisons. Conclusion: Modelling TEWL experimental data in a compartmental analysis framework provides valuable parameterized information for characterising and comparing results. Numerical parameters derived on solid theoretical assumptions are reliable indicators for many situations, as long as those assumptions are not violated. The proposed bicompartmental model may also be suitable for other cutaneous water balance related variables, such as capacitance or conductance, although eventually based on distinct model assumptions. In any case, this modelling conceptualisation seems to render valuable insights into the kinetic description of the main processes involved in the net evaporation and water distribution within the complex human skin hydration process.

Assessing the in vivo impact of a gel sanitizer on the epidermal barrier dynamics

“…A fim de melhorar a precisão das medições da PTEA, outras abordagens dinâmicas têm sido sugeridas. Os testes de acumulação de humidade (MAT) [9] , de sorção/dessorção [10] e de oclusão plástica (POST) [11] são exemplos relevantes que servem como base conceptual para o modelo aqui aplicado, permitindo uma descrição quantitativa mais precisa do balanço de massa de água cutânea ao longo do tempo [12][13][14] . O presente estudo avalia o impacto da utilização de um gel desinfetante de base alcoólica sobre a função de 'barreira' epidérmica, usando uma abordagem de modelação cinética das curvas de dessorção da PTEA após um POST.…”

“…TEWL was continuously measured for 30 minutes, at a frequency of 0.1 Hz (one measurement every ten seconds) and modelled by a bicompartment model. This model, first proposed in 1999 [12] , considers the barrier and inner layers of the skin as two different water compartments. The first compartment is the skin barrier with low water content, while the second represents the innermost layers of the skin with higher water levels.…”

“…In order to improve the precision of TEWL measurements, other dynamical approaches have been suggested. The moisture accumulation test (MAT) [9] , the sorption/desorption test [10] , and the plastic occlusion stress test (POST) [11] are relevant examples serving as the conceptual basis for the compartmental model here applied, allowing a more accurate quantitative description of the cutaneous water mass balance over time [12][13][14] . This study evaluates the impact of the use of an alcoholbased gel sanitizer on the epidermal 'barrier' function, using a kinetic approach of TEWL desorption curves following a POST test.…”

Assessing the impact of the regular use (4 weeks) of an alcohol-based hand sanitizer on TEWL and epidermal hydration

“…A PTEA, expressa em (g/m 2 / h) foi medida com um aparelho Tewameter TM300 (Courage + Khazaka Electronics GmbH, Colónia, Alemanha); hidratação epidérmica superficial (HS) expressa em unidades arbitrárias (UA), utilizando o dispositivo MoistureMeter-SC® (Delfin Technologies Ltd, Kuopio, Finlândia) e hidratação epidérmica profunda (HP), expressa em unidades arbitrá-rias (UA), utilizando o dispositivo MoistureMeter-D® (Delfin Technologies, Finlândia). As curvas de dessorção da PTEA foram ajustadas a um modelo cinético bi--compartimental já descrito [13][14][15] , utilizando o software MatLab (Toolbox MATLAB e Estatística Versão 2011, The MathWorks, Inc., Natick, Massachusetts, EUA), de onde foram extraídos dois parâmetros cinéticos: t 1/2 evap (tempo de meia-vida de evaporação) e DWM (massa de água dinâmica). A evolução dos valores absolutos da PTEA e dos parâmetros cinéticos derivados das curvas foi comparada para ambas as mãos e entre as mãos controlo e teste pelo teste teste não paramétrico de Wilcoxon para amostras emparelhadas (p<0.05).…”

“…TEWL, expressed in (g/m 2 /h) was measured with a Tewameter TM300 (Courage + Khazaka Electronics GmbH, Cologne, Germany); superficial epidermal hydration (SH) expressed in arbitrary units (AU), using the MoistureMeter-SC ® device (Delfin Technologies Ltd, Kuopio, Finland); and deep epidermal hydration (DH) expressed in arbitrary units (AU), using the MoistureMeter-D ® device (Delfin Technologies, Finland). The TEWL desorption curves were fitted to a bi-compartment kinetic model previously described [13][14][15] , using MatLab software (MATLAB and Statistics Toolbox Release 2011, The MathWorks, Inc., Natick, Massachusetts, USA), from which two kinetical parameters were extracted: t 1/2 evap (half-life of evaporation) and DWM (dynamic water mass). The evolution of the absolute TEWL values and of curve-derived kinetic parameters were determined in each hand and between control and test hands by the Wilcoxon signed-rank test (IBM SPSS Statistics for Windows, 20.0 version, Armonk, NY: IBM Corp).…”