MEASUREMENT OF LUNG DIFFUSING-CAPACITY AND FUNCTIONAL RESIDUAL CAPACITY IN LAMBS DURING THE FIRST POSTNATAL MONTH

The diffusing capacity of the lung for carbon monoxide (D-LCO) is an i mportant index of lung function but is not easily measured in spontane ously breathing animals with small lung volumes. Our aim was to devise a simple rebreathing method that would allow us to make serial measur ements of D-LCO in spontaneously breathing lambs during their first mo nth after birth. By adding He to the rebreathing gas mixture, we were also able to measure functional residual capacity (FRC), enabling us t o normalize D-LCO with respect to FRC. We have compared FRC measured b y the rebreathing technique with that measured by a closed-circuit hel ium dilution method (FRC(cc)). Using the rebreathing method we found h ighly significant positive correlations between D-LCO and body weight (r = 0.70, P < 0.001) and between FRC and body weight (r = 0.79, P < 0 .001). There was no significant change in D-LCO/FRC over the first pos tnatal month; the mean value was 8.1 +/- 0.6 mL/min/mmHg/mL. Rebreathi ng FRC was highly correlated with FRC(cc) (r = 0.88, P < 0.001), but w as lower than FRC(cc) by about 18%. In normal lambs D-LCO and FRC, but not D-LCO/FRC, increased during the first month after birth, suggesti ng that the increase in D-LCO parallels lung growth. We conclude that the modified rebreathing method is suitable for measuring D-LCO in sma ll uncooperative spontaneously breathing animals. (C) 1994 Wiley-Liss, Inc.