Improved Estimation of Sweating Based on Electrical Properties of Skin

Abstract

Skin conductance (SC) has previously been reported to correlate strongly with sweat rate (Swr) within subjects, but weakly between subjects. Using a new solution for simultaneous recording of SC, skin susceptance (SS) and skin potential (SP) at the same skin site, the aim of this study was to assess how accurately sweat production can be estimated based on combining these electrical properties of skin. In 40 subjects, SC, SS, SP and Swr by skin water loss was measured during relaxation and mental stress. SC and Swr had high intraindividual correlations (median r = 0.77). Stepwise multilinear regression with bootstrap validation lead to a sweating estimation model based on the sum of SC increases, the SP area under the curve and the SS area under the curve, yielding an interindividual accuracy of R(2) = 0.73, rmse = 12.9%, limits of agreement of +27.6, -30.4% and an intraclass correlation coefficient of 0.84. Bootstrapping of training and test-sets gave median rmse = 15.4%, median R(2) = 0.66. The model was also validated for intraindividual variability. The results show that estimation of sweating is significantly improved by the addition of SS and SP measurement.

Electrodermal responses to discrete stimuli measured by skin conductance, skin potential, and skin susceptance

“…It was made up of a small front-end electronic box connected by means of a National Instruments DAQ card-NI USB-6211 to a PC laptop running software custom written in LabVIEW, v. 14, analogous to the system presented in. 18 It consists of one measuring electrode (M), one reference electrode (R), and a current-sink electrode (C). The current-sink electrode together with the reference electrode serves to provide a unipolar AC SC measurement below the measuring electrode.…”

“…A complete list of all the parameters extracted from EDA responses and included in the data analysis, is given in Table 1. 18 Schematic of the setup for simultaneously measuring SP, SC, and SS at the same skin site. NI USB DAQ card converts the digital sine wave signal to analog then sends through (AO_0) channel to front-end electronic box (for injection of current to the skin), and receives back from the box and converts to the digital through (AI_0 & AI_1) channels (for pick up of voltage from the skin).…”

The microfluidics of the eccrine sweat gland, including biomarker partitioning, transport, and biosensing implications

“…Such speculation is further supported by decades of sweat rate measurements by skin conductance, where a wearable sensor is placed over skin and prevents evaporation, which provides a real time measurement of Na þ and Cl À concentration in the duct and importantly for which there is clearly no inflection point in plots of skin conductance vs. increasing sweat rate. 17,19 Therefore, if the data in Figure 4(b) were re-measured with a wearable electronic device (hydrated skin with no evaporation), it is speculated that the concentration increase observed at low sweat rates might not appear.…”

“…To predict sweat rate, Na þ or Cl À can be directly measured using ion-selective electrodes 6,7 or electrical conductivity of the sweat can be measured, since Na þ and Cl À are the dominantly abundant ions in sweat. Sweat rate or sweat incidence tests based on skin electrical impedance 16,17,19,20 are appearing increasingly in wearable electronics and also rely on measuring the electrical conductivity of sweat. The stratum corneum is highly electrically resistive and therefore a sweat duct filled with salty sweat provides the lowest electrical resistance pathway into the body.…”

“…15 Wearables can also easily measure the change in sweat generation rate by skin impedance. [16][17][18][19][20] However, sweat generation rate does not predict actual biomarker sampling intervals without a detailed microfluidic and transport model between the sweat glands and sensors.…”