EFFECT OF SKIN TEMPERATURE ON MULTIFREQUENCY BIOELECTRICAL-IMPEDANCE ANALYSIS

This study assessed the effects of changes in skin temperature on mult ifrequency bioimpedance analysis (MF-BIA) and on the prediction of bod y water compartments. Skin temperature (baseline 29.3 +/- 2.1 degrees C) of six healthy adults was raised over 50 min to 35.8 +/- 0.6 degree s C, followed by cooling for 20 min to 26.9 +/- 1.3 degrees C, by usin g an external heating and cooling blanket. MF-BIA was measured at both distal (conventional) and proximal electrode placements. Both distal and proximal impedance varied inversely with a change in skin temperat ure across all frequencies (5-500 kHz). The change in proximal impedan ce per degree centigrade change in skin surface temperature was simila r to 60% of distal impedance; The change in measured impedance at 50 k Hz erroneously increased predicted total body water (TBW) by 2.6 +/- 0 .9 liters (P < 0.001) and underpredicted fat mass by 3.3 +/- 1.3 kg (P < 0.0001). Computer modeling of the MF-BIA data indicated changes in predicted water compartments with temperature modifications; however, the ratio of extracellular water (ECW) to TBW did not significantly ch ange (P < 0.4). This change in impedance was not due to a change in th e movement of water of the ECW compartment and thus probably represent s a change in cutaneous impedance of the skin. Controlled ambient and skin temperatures should be included in the standardization of BIA mea surements. The error in predicted TBW is <1% within an ambient tempera ture range of 22.3 to 27.7 degrees C (72.1-81.9 degrees F).