Method for determination of pulmonary gas exchange in connection with birth

An apparatus built on the "open" system for determination of pulmonary gas exchange in the newborn infant after birth is described. At four-minute intervals diluted expired air (5-7 1/min) was collected in bags. The oxygen and carbon dioxide fraction in the bags were analysed with a Nyons Diaferometer (working on the principle of thermoconductivity). In calibration experiments using a gas-mixing technique a high degree of linearity was found, both in the determination of the fraction of oxygen and carbon dioxide (r equal to 0.9996). Reproducibility from duplicate readings was also good (for oxygen determination 0.9% and for carbon dioxide determination 0.8%). Duplicate determinations performed on infants with the same degree of motor activity resulted in an estimated error of the method of 5.8% for VO2 and 7.8% for VCO2 respectively. A metabolic chamber was used to control environmental temperature. The air temperature and wall temperature in the chamber were regulated by water from a thermostatically controlled waterbath and were kept equal within 0.5 degrees C. As the method for determination of the fraction of oxygen and carbon dioxide is not specific, other gaseous materials exhaled by the infants influence the measurements and nitrous oxide was found to interfere with the determinations, and made VO2 and VCO2 determinations in these patients impossible. Experience from more than 50 investigations on newborn infants has shown that the method is well suited to this particular type of study.