Studies on skin blood flow and evaporative water loss : a bioengineering approach

Abstract: Skin blood flow (SBF), temperature, evaporative water loss (EWL) and skin conductance (SC) measured during stimulus-response experiments reveal valuable information regarding the skin's regulatory capacity. SBF and EWL play powerful roles in keeping the human body within an adequate temperature range. EWL and SC reflect the thermal and mental state of the subject. SBF, EWL and SC were measured using noninvasive laser Doppler flowmetry, vapour pressure gradient estimation and a DC-voltage method, respectively.Short acoustic stimuli evoked responses in both EWL and SC at the palm; their response amplitudes were strongly correlated (r = 0.87). Both latency and time to the peak of EWL responses were delayed by 1.1 sec and 2.3 sec, respectively, in comparison to SC responses.EWL measurements at the forearm revealed rhythmical variations in the recorded signal. The period was approximately 0.74 sec at rest. At a higher evaporation rate, induced by exercise, a longer period (0.84 sec) was detected. The period was independent of the sex of the subject and ambient temperature, and remained unchanged for repeated measurements on the same subject.In the skin temperature range 12 to 38°C, the relationship between SBF and local temperature, at the thigh, palm and fingertip, was best fitted to exponential equations. For a narrower temperature interval (23 to 36°C), palmar SBF and temperature followed linear equations within subjects. However, a large variability in regression coefficients was revealed between subjects. When SBF values were normalized to room climate level, they correlated strongly to skin temperature values (r=0.88).Radiative cooling (17°C) of the palm from room climate conditions doubled local heat loss and left SBF virtually unchanged. When cold convective air currents (19°C, 0.5 or 1.0 m/s) were applied, SBF decreased to 60 and 53% while heat loss dropped to 68 and 70%. Rewarming after local cooling revealed discrepancies'in the restoration of both SBF and skin temperature between the measurement sites.