This project aims to study obese (Body Mass Index greater than or equal to 30 kg/meter-squared) and normal weight (BMI less than or equal to 25 kg/meter-squared) adults to determine possible obesity-related differences in 1) regional body temperature heterogeneity (i.e., presence of localized areas of heat retention), 2) the extent to which locally retained heat may be co-localized with deep fat depots, 3) the effectiveness of the hands as dissipaters of heat, and 4) the ability of approaches that alter heat dissipation to modify deep-body temperature heterogeneity.? ? It is hoped that the results of this study will provide preliminary evidence for future studies that attempt to facilitate weight loss in obese subjects through effective, guided applications of heat management.? ? Over the past year the project, two specific methods to study human thermogenesis and human reaction to local cold stress are under development and validation for clinical use. ? ? 1. Recovery-enhanced infrared imaging of the fingers.? ? Preliminary analysis shows that different subjects exhibit different reactivity times to cold stress, reflecting the tonus of the blood vessels of their fingers. More safe and adapted for obese patients, a cooling unit was designed and manufactured during 2006 and will be moved to the Clinical Center to further study blood vessel reactivity in obese patients.? ? 2. Microwave thermometry.? ? The specificity of microwave radiometry to deep temperature changes was evaluated for its use in assessment of human body temperature heterogeneity. The rationale is the sensitivity of passive microwave radiometry to the natural electromagnetic radiation of living tissue. The intensity of radiation received is proportional to the radiometric temperature (RT), defined as a weighted mean of tissue volume temperature. A 1.15 GHz antenna and an 8-12 micron infrared (IR) detector (RESLtd, Russia) were placed in contact with areas of the right arm. Using a 4s acquisition time, the estimated accuracy for internal RT in 25cc of tissue was 0.15 degrees C. In ten experiments with hands (30-34 mm thick), infrared and radiometric temperatures of the palm were monitored for 6 min at room temperature. The measurements were repeated for 5 min, while a 17 degrees C cold patch (ThermoTek, USA) was applied to the dorsum of the hand. The measurements were repeated again with the patch at 40 degrees C, and one final time with a 17 degrees C cold patch. Only the microwave sensor placed at the palm followed the same curve as the temperature of the dorsally-placed temperature patch.? ? In five experiments with the upper arm (95-120 mm thick), both IR and RT were monitored for 3 min to establish a baseline, and then during recovery following 2 min of moderate exercise (pushups). After an hour break, the exercises were repeated, followed immediately by 15 min of cooling of the ipsilateral palm in the presence of a mild vacuum at 17 degrees C (AVAcore Technologies, USA), and temperature measurements, as before. After the completion of exercise-evoked heating, the rate of RT decrease at the triceps was 0.012 degrees C/min. With the addition of palm cooling, the rate of temperature decrease during recovery was 0.06 degrees C/min. Only the microwave antenna was sensitive to body temperature changes due to application of a distant heating/cooling patch and exercise.? ? These methods were developed under protocol """"""""Body Heat Content and Dissipation in Obese and Normal Weight Adults"""""""" (Principal Investigator: J. Yanovsky, M.D.; Lead Investigator: A. Gorbach, Ph.D.)
