Body Heat Content and Dissipation in Obese and Normal Weight Adults

Detailed Summary

This study will investigate how different parts of the body lose body heat and will measure the heat released by specific areas such as the limbs and abdomen. Animal studies suggest that dissipation of body heat may affect energy expenditure, and therefore, body weight. This study will explore the relationship between obesity and heat in humans. Healthy people 18 years of age and older who are of normal weight or who are obese and who are not taking medications for obesity-related medical conditions may be eligible for this study. Candidates must have a body mass index (BMI) between 18 and 25 kg/m2 for normal weight subjects or a BMI greater than 30 kg/m2 for obese subjects. All candidates must weigh less than 300 pounds. Women must have a normal menstrual cycle or be postmenopausal. Participants undergo the following procedures in a single day on an outpatient basis: * Medical history, physical examination, blood and urine tests and electrocardiogram. * DEXA and MRI scans of the trunk and limbs to measure the amounts of muscle, bone and fat in the body. For the DEXA scan, the subject lies on a table while a very small dose of x-rays is passed through the body. For the MRI, the subject lies on a table that is moved into a steel cylinder. A magnetic field and radio waves produce images that are used to measure fat in the trunk of the body, thighs, and arms. * Infrared photography of hands, front of thigh, and abdomen. A special camera is used to measure the heat leaving the body. * Bicycle exercise test. The subject exercises on a stationary bicycle while the heart rate, heart rhythm, blood pressure and oxygen consumption are measured. The pedal resistance is increased gradually until the subject can no longer exercise and then the resistance is gradually decreased for cool-down. Participants who qualify for the second part of the study undergo the following procedures during a 5-day in-hospital stay: * Temperature measurements. Body temperature is measured in the ear canal. Skin temperature is measured with small round adhesive temperature-sensing patches placed on the abdomen and limbs for up to 5 days. * Measurement of body radiowaves. A remote sensing device is used to measure microwaves that are naturally released from the body. * Infrared photography of hands, front of thigh and abdomen is done several times during the study. * Application of mild coolness to hands, thigh and abdomen. The subject's hand is exposed to mild coolness first by immersion in cool water, then by a cool-water spray, then by a cooled pad placed on the hand, and finally, with a device applied to the hand that cools and has a gentle vacuum. The abdomen and thigh are similarly exposed. During each test, an infrared camera records how heat is released by the body. * Temperature effects of a "meal." The subject drinks lemon-flavored sugar water to measure the body's response. * Bicycle exercise test. The subject exercises on three different occasions. During or after some of the tests, mild cooling is applied to the abdomen, front of the thigh, or hands. * Measurement of exhaled air (indirect calorimetry). The subject wears a hood that collects and analyzes exhaled air for 15- to 30-minute periods. * Photography and videotaping. The subject is photographed and videotaped. The images do not include views of any private parts, and the subject's identity is protected.

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