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ENERGY METABOLISM CORE
The function of the Energy Metabolism Core is assessment of the components of energy metabolism: energy intake, energy absorption, fuel oxidation and energy expenditure. These measurements require both components of the Core: the Human Respiratory Chamber and the Energy Metabolism Laboratory. Dr. Boozer, Director of the Energy Metabolism Core, also has an indirect calorimeter system for small animals in her own laboratory that is available for collaborative studies involving measurement of these components in rodent models.
Human Respiratory Chamber.
The human respiratory chamber is used for 24-hour assessment of energy expenditure (EE) and its components as well as substrate (fat and carbohydrate) oxidation. These measures are important for nutrient and energy balance studies in both normal and disease states. Examples of potential studies that could make use of these determinations include: diagnosis of thyroid abnormalities or wasting, determination of factors contributing to obesity such as reduced fat oxidation or low EE, effects of normal life processes such as aging or pregnancy on energy balance, and effects of various treatments for obesity on substrate oxidation and EE. Indirect calorimetry techniques can also be used to determine factors contributing to daily energy expenditure such as frequency and intensity of physical activity/exercise, which are major variables in total EE, thermic effect of food, drug treatment, etc.
Design. The Columbia Human Respiratory Chamber, initiated by Drs. Heymsfield and Dr. Pi-Sunyer in the late 1980's, was constructed by Yungao Sun for his Ph.D. thesis (Engineering Department, Columbia University). The original design was for a 3-room chamber to allow a subject to move from room to room during a single 24-hour test. In 1998, this chamber was redesigned by Dr. Boozer with the help of Dr. Ming Sun (MiniSun Consulting) and Kuan Zhang (Columbia University). When completed, the new design will include two independent single-room chambers. One is in final testing stages, and the second will be completed during the next year. Each chamber will consist of an air-tight, temperature-controlled room with an entrance door containing an inflatable seal, an air-lock pass-through for food, a sink and toilet, a television, table, chair, bed and telephone. Air is continuously pulled through the room by a vacuum pump located outside the room with the rate of flow continuously measured by a mass flow meter. A sample of the purged air is then pulled through a specially designed condenser to remove moisture before measurement of percent O2 and CO2 by oxygen and carbon dioxide analyzers. Fans inside the chamber constantly mix the room air and a special multi-channel air sampling system ensures that the air purged from the chamber is a representative sample of the air in the chamber. Temperature of the room is precisely controlled by computer-regulated chilled-water and heating panels. All data is recorded and processed on-line by a computer program that measures variables such as oxygen and carbon dioxide gas concentrations, flow, temperature and barometric pressure and computes EE in real time. Errors caused by environmental fluctuations and electrical noise/interference are removed using a number of techniques including signal processing and system identification. This results in high accuracy (error SD < ±1%) and fast response time for EE and RQ calculations. Energy expenditure (EE) and fat and carbohydrate oxidation are calculated by standard formulae. (Protein oxidation is determined in the Energy Balance Laboratory by nitrogen analysis of urine collected during the test.) Energy balance is assessed by subtracting total EE from energy intake determined by calculation or measurement of the caloric content of the food consumed. Routine tests of the respiratory chamber include leak tests using dry ice as a CO2 source, calibration of the analyzers using a gas mixing pump and O2 and CO2 recovery tests performed by burning alcohol.
Measurement of Physical Activity. Total energy expenditure includes: resting metabolic rate, thermic effect of food, and energy expenditure due to physical activity. Of these, the most variable component of energy expenditure is that due to physical activity. In order to quantify this variable, a special floor is installed in one of the chambers. The floor rests on four precision force transducers which send continuous signals to the computer. When the subject exercises, signals indicating the relative force on these transducers are transmitted to the computer for calculation of mechanical work thus produced and the EE due to physical activity. In addition, the location of the subject on the floor, the distance traveled, and the amount of work performed horizontally and vertically can be obtained on minute-by-minute basis.
Energy Metabolism Laboratory.
The Energy Metabolism Laboratory is complementary in function to indirect calorimetry in providing precise measurement of energy intake by bomb calorimetry and in assessing 24-hour protein oxidation from nitrogen analysis of urine collected during respiratory chamber tests. This data is necessary to calculate non-protein RQ in indirect calorimetry studies such as one currently being conducted by Dr. Boozer to determine the effect of dietary fat on fat balance in lean women. By analyzing nitrogen in both food and the urine, protein balance can also be determined. These assessments have been useful in a variety of studies such as one by Dr. Geliebter to determine the effect of strength training on preservation of lean body mass in subjects undergoing caloric restriction. Another study by Drs. Kotler and Engelsen used nitrogen balance data to determine the effect of a potential anti-cryptosporidia passive immune therapy for patients with HIV and cryptosporidia infection. Dr. Albu, studying the differential metabolic effects of insulin resistance and non-resistance in obesity, used this laboratory’s analyses of urinary nitrogen and energy value of formula to assess energy and substrate utilization during insulin clamp studies.
The Energy Metabolism Laboratory also provides direct total carcass composition analysis of animals including fat, water, protein and mineral (ash). This information is important for many nutritional and energy balance studies. It also provides a method for validation of in vivo body composition analyses such as DXA or neutron activation conducted in collaboration with Dr. Heymsfield and other investigators in the Body Composition Core and at other institutions.
CONTACT INFORMATION:
Carol N. Boozer, D.Sc.
Obesity Research Center: Babcock 1029
St. Luke’s-Roosevelt Hospital Center
1111 Amsterdam Avenue
New York, NY 10025
Tel:(212) 523-4174 (office); -4994 (chamber)
Fax:(212) 523-4830
E-mail: cnb7@columbia.edu