EFFECT OF A COLD SKIN AND WARM AIR TEMPERATURE DIFFERENCE ON ESTIMATION OF BODY VOLUME USING AN AIR-DISPLACEMENT PLETHYSMOGRAPH

Abstract

Air-displacement plethysmographs (ADP) have been used to predict body density (BD) (mass/volume) by estimating body volume (BV). This estimate is made by measuring changes in air pressure and applying Boyle's Law (pressure-volume relationship). The final estimation of BV is corrected by adjusting for the influence of isothermic air found on the surface of the skin. To reduce the measurement error associated with having warmer than expected air on or near the skin, it is recommended that individuals refrain from exercise and be minimally clothed prior to testing with an ADP. It is not clear, however, how having cold skin temperatures, in a warm ADP environment, might affect BV estimates. PURPOSE To determine if a cold skin and warm air temperature difference affects estimation of BV using an ADP. METHODS Two estimates of BV were made using an ADP on 16 men and 16 women (23.1±2.4 yrs). The first was obtained while the skin was warmer (SW), 32.7854±1.4433°C. The subsequent while the skin was significantly (p < 0.01) cooler (SC), 29.4876±1.4568°C. Skin cooling was done by having the participant sit in front of fans in an air-conditioned, isolated, room (16.49±0.54°C) for 15 min. Means were compared using pair t-tests and Bonforoni corrections procedures. RESULTS Skin temperature was 1.8405±1.3954°C warmer and 1.0234±1.4759°C colder than the air in the ADP during SW and SC, respectively. BV estimates were significantly lower following SC (67.4019±16.8578 vs. 67.5597±16.8683L, p < 0.01). This resulted in a significantly higher estimation of BD (1.0455±0.0199 vs. 1.0437±0.0194kg/L, p < 0.01) and lower predicted percent body fat (23.6405±9.1540 vs. 24.4362±8.9179%, p < 0.01) after SC. CONCLUSION Cooler than expected skin, in comparison to ADP air temperature, resulted in a lower estimate of BV and under prediction of percent body fat. While the results are statistically significant, they are small and perhaps without practical significance. They do suggest that BV estimates using an ADP can be optimized if care is taken to assure the skin is not cold in comparison to the air in the ADP.