ABSTRACT. We measured the oxygen consumption, car-STPD, standard temperature, standard pressure, dry bon dioxide production, and respiratory quotient during the IR, infrared combustion of a known mass of anhydrous ethanol and methanol to assess the accuracy of an open-circuit flowthrough system. Continuous measurements were made of the mass of alcohol burned, the velocity of gas flow through the apparatus, and simultaneous measurements of the fractional concentration of oxygen, carbon dioxide and nitrogen of the inlet and outlet gas using paramagnetic oxygen analyzer, infrared carbon dioxide meter, and mass spectrometer. Standard respiratory and stoichiometric equations were used to calculate the oxygen consumption, carbon dioxide production and RQ for the mass of absolute alcohol combustion per unit time. In a series of 12 consecutive laboratory experiments (on 7 days), the measured values of gas exchange (similar to the rate of respiratory gas exchange by an infant of 1-4 kg) were in agreement within 5% of the true values for ethanol and methanol combustion, confirming the validity of the open-circuit method. The paramagnetic oxygen analyzer and the mass spectrometer gave similar oxygen consumption results and differed very little when the rate of absolute alcohol combustion was used to quantify the accuracy of the complete measurement system. A positive measurement error was observed for the carbon dioxide production results from both the IR meter and mass spectrometer, with the result that the respiratory quotient measurements were 3.4-4.7% higher than the true value. The mass spectrometer gave more precise oxygen consumption results, whereas smaller variance of carbon dioxide production measurements was observed using the infrared C 0 2 meter. The sources of error and methods to reduce the overall system error were considered. By using a rigorous set of calculations we showed that the rate of combustion of a known mass of absolute alcohol was a suitable laboratory method for validation of respiratory gas exchange measurements made The requirements for the accurate determination, and the sources of error in clinical studies of metabolic rate in man were laid down in detail over 75 yr ago by Atwater and Benedict, and in infants by Levine, Gordon, Karlberg, and Briick (1-6). The extraordinarily complex calibration equipment and the detailed calibration results these authors published have rarely been quoted in contemporary neonatology literature (7). Moreover, the open-circuit systems currently used to measure metabolic rate of the newborn when only the head or face of the baby was enclosed in a chamber or mask have yet to be routinely calibrated in a standard manner.In our study, we describe a method to measure VO,, VCO,, and RQ with the flow-through system in a controlled laboratory environment when the rate of absolute alcohol combustion was used to quantify the accuracy of the complete measurement system. In addition to our major objective of evaluating the whole open-circuit system, we also partitioned th...
