Infrared Thermography Diagnostics of Subcutaneous Thermogenerators of Non-Shivering Thermogenesis

Changes in skin temperature induced by the factors causing the activation of non-shivering thermogenesis (NST) were quantitatively described, using dynamic infrared thermography, in 8 physically active men (the mean age was 24.8 ± 4.0 years, body mass index (BMI) was 23.6 ± 0.44) at different body surface locations (the anterior and posterior parts of the neck, the supraclavicular fossae, the sternum, and the interscapular area). During the experiments, the subjects had to undergo, on different days, a glucose-tolerance test, they were locally exposed to cold (feet immersion in water at 0°C for 1 min) and had to perform a single breath-hold test, as well as the aerobic (Ramp) and anaerobic (Wingate) performance tests. The obtained results have shown the presence of thermogenerators, which can cause non-shivering thermogenesis in the human body in response to stimuli of sympathetic and stressogenic origin. A thermogenerator in this context is understood as a cluster of homogeneous cells located subcutaneously or in deeper-laying tissues characterized by elevated heat production whose flow of infrared radiation reaches the body’s surface and shapes a particular thermographic portrait. Deep individual differences have been identified between responses of thermogenerators to the same stimuli. These responses do not differ in synchronicity or intensity and, presumably, depend on a subject's adaptive experience, i.e., on the subject’s life conditions and other epigenetic factors. It has been shown that the thermogenerators located in the supraclavicular region and associated with the brown adipose tissue (BAT) have the highest sensitivity to the tested set of stimuli. A close functional connection has been identified between these thermogenerators and the thyroid gland. Some not at all trivial relationships have been detected between all the studied thermogenerators, and further studies are needed in this area. In particular, we cannot detect any similarities between maximal aerobic and maximal anaerobic exercises in terms of thermogenic response. The glucose response was isolated relative to other stimuli. The data obtained make us think not only about BAT but also about the role of other tissues in energy metabolism regulation. For instance, close attention should be paid to the muscle tissue which has uncoupling protein UCP3. Based on the results, we cannot make an unequivocal conclusion about the nature of investigated thermogenerators. Yet we hope that the widespread usage of non-invasive and safe thermography will allow us to accumulate scientific facts that are necessary to make differential diagnosis for various types of thermogenerators in the human body.