A whole body transportable indirect calorimeter for human use in the tropics.

A transportable, whole body indirect calorimeter, designed for use in the tropics, is described. The calorimeter was built to study energy expenditure of people having chronically or acutely low levels of food intake, and it will help to determine energy adaptations made by individuals with restricted food intake. The calorimeter comprises two units: a 27 m3 ventilated chamber connected to an office housing control and monitoring equipment. The system also allows the experimenter to assess the rate of energy expenditure by means of a ventilated hood or a baby respiration chamber. The incoming air flow rate is variable and is typically set at approximately 30 l/min. Carbon dioxide production (VCO2) and oxygen consumption (VO2) are continuously monitored by means of differential gas analysers via a computerized data acquisition unit. Gas production/consumption rates are measured with a delay of 80 s, the complete response to step changes in VCO2 or VO2 consumption being calculated over 15 min using the rate of change terms in the gas exchange equations. The total electrical power required for the whole system is 12 kW. The calorimeter has been functioning for nearly 4 years in a rural village of The Gambia during which ambient temperatures have ranged from 16 to 44 degrees C and dewpoints from -8 to 24 degrees C. The performance and accuracy of the calorimeter were tested using 20 per cent CO2 in N2 infusion and butane burning. Agreement between the theoretical and the measured values was found to be 99 per cent for VO2 and 100 per cent for VCO2 with a precision for both gases of +/- 10 ml/min over a 1-h period

Metabolic rate at rest and during sleep in a thermoneutral environment.

This study characterised the pattern of oxygen consumption (VO2) in healthy infants and children asleep and awake (at rest) in a thermoneutral environment. Measurement of respiratory gas exchange (VO2 and VCO2) was made using an open circuit flow through system of indirect calorimetry with a specially designed facemask for the collection of exhaled breath. Fifty two healthy subjects aged 4.5 months to 12.8 years were studied for 15-20 minutes; 18 during sleep and 34 at rest (awake). There was a curvilinear relation between VO2 and age in the two groups and children aged 2 years or less had the highest values. The value of VO2 was significantly higher in the awake subjects (12.5-15.0 ml/min/kg compared with 7.5-9.0 ml/min/kg in sleeping children). Comparison of the regression lines after log transformation of these data showed a significant difference in VO2 of resting and sleeping subjects up to the age of 9.5 years