The effect of ambient air temperature on whole-body bioelectrical impedance.

It has previously been shown that extreme changes in ambient air temperature can affect whole-body bioelectrical impedance. The purpose of this study was to determine if more moderate changes in ambient air temperature, such as those experienced in most laboratory settings, would also affect bioelectric impedance analysis (BIA). In addition, to elucidate the mechanism responsible for changes in BIA with ambient air temperature, both skin blood flow (SBF) and the electrode-skin interface temperature were independently manipulated to determine their effect on BIA. During the first part of the study, nine healthy volunteers had their BIA measured in five different ambient air temperatures (15, 20, 25, 30 and 35 degrees C). Mean BIA was 513 ohms under the 15 degrees C condition and decreased significantly (p < 0.05) to 486 ohms in the 35 degrees C trial. However, no significant change was found in mean BIA between the 20 and 25 degrees C trials, which is the temperature range seen in most laboratories. Thus, moderate changes in ambient air temperature have only minor effects on BIA. In the second and third parts of the study, the electrode-skin interface temperature and SBF were independently manipulated using ice packs and electric heating pads placed over the four BIA electrodes. The results showed that BIA was inversely related to SBF (r = -0.95), and strongly suggest that changes in SBF, not electrode-skin interface temperature, are responsible for the changes seen in BIA.