Quantitation of energy expenditure by infrared thermography.

The objective of this study was to adapt infrared thermography (IRT) to measure heat loss in human beings. IRT images were digitized and a mean body surface temperature was computed; heat losses caused by radiation, convection, and evaporation were calculated by using these data. Because subjects were standing during the procedure a small amount of heat was conducted through the feet; this heat was ignored. Total heat loss measured by IRT was not significantly different from values calculated from simultaneous indirect calorimetry (IC) determinations in fasting health subjects and in postsurgical patients receiving a constant infusion of energy. In healthy subjects, after eating the patterns of response to IRT and IC were as predicted from previous direct calorimetry data. Heat loss measured by IC increased first, 30 min postprandially, followed by an increase in heat loss at 60 min as measured by IRT. It was concluded that IRT as a noninvasive method can be used to quantitate heat loss in human beings.