Quantitative lung morphology in newborn mammals

We have examined the lungs of eleven species of newborn mammals by quantitative morphometric techniques and related the findings to body weight (BW) and O(2) consumption (Vo2 is found to be proportional to BW(0.88); this exponent is significantly greater than the value of about 0.73, repeatedly found for adult mammals. Lung volume (LV) is essentially proportional to BW, and neonatal alveolar size - as indicated by mean chord length - is nearly constant among species and independent of BW. Thus the respiratory surface area (SA) is not proportional to Vo2, as in adult mammals, but to Vo2(1.23). Neonates of small species have lower SA/Vo2 ratios than adult mammals, possibly owing to constraints of surface forces on alveolar size. Newborn members of larger species have SA/Vo2 values in excess of the adult range. Published data on human newborn lung dimensions suggest that the human infant may have an unexpectedly low SA/Vo2 value in relation to BW. Whether this is a valid finding, or whether it derives from methodological differences between studies cannot be ascertained from the available data.