Effect of ambient temperature on bioimpedance from a wearable sensor patch

Wearable bioimpedance sensors are promising tools for long-term home monitoring, but their measurements may be affected by ambient temperature and anatomical site. This study examined how cold and warm exposure influence local skin impedance measured by a miniaturized patch at four body locations.Twelve healthy volunteers (4 female, 8 male; 18-40 years) wore four Re:Balans ® Insight patches (upper back, upper arm, thigh, lower leg) for approximately 30 h. On two consecutive days, each participant underwent 1 h of exposure to either a cold (4 °C) or warm (37 °C) climate chamber in counterbalanced order, with preand post-exposure baseline periods. Multi-frequency bioimpedance (24 frequencies, 5.8-504 kHz) and skin temperature were recorded continuously and aligned to the 1 h climate chamber period. Two representative frequencies (7.4 kHz, 403.4 kHz) were analyzed for relative impedance change, time trends, and temperature sensitivity ∆Z/∆T . Non-parametric tests were used to compare locations and conditions.Cold exposure decreased skin temperature by about -3.2 to -5.2 • C and increased impedance at all sites, whereas warm exposure increased skin temperature by about +1.6 to +2.4 • C and decreased impedance at all sites. Relative and absolute changes were larger at 7.4 kHz than at 403.4 kHz. Location-dependent differences were small during cold exposure but more pronounced during warm exposure, with a moderate-to-large effect between upper back and lower leg that did not remain statistically significant after multiple comparison correction. All sites showed negative temperature sensitivity; limb locations exhibited higher |∆Z/∆T | and stronger impedance-temperature linearity than the upper back.Local skin impedance measured by wearable patches is sensitive to changes in ambient temperature in a frequency-and site-dependent manner. Extremity sites appear suitable for temperature-or blood-flow-related applications, whereas the upper back may be advantageous where temperature-induced variability should be minimized.