Postnatal development of respiratory function in lambs studied serially between birth and 8 weeks.

We have quantified developmental changes in major aspects of respiratory function in 12 pentobarbitone-sedated lambs by making repeated measurements during the first 8 postnatal weeks, between term birth and post-weaning. Pulmonary diffusing capacity for CO increased with age due to increases in both the diffusing capacity of the alveolar capillary membrane (Dm) and pulmonary capillary blood volume (Vc). Total lung capacity measured at a lung inflation pressure of 30 cmH2O decreased from 74.4 +/- 3.2 ml/kg at 3 days to 47.2 +/- 2.9 ml/kg at 8 weeks. Static respiratory system compliance, measured between FRC and TLC fell rapidly during the first 3 weeks, then remained unchanged; the early postnatal fall was largely due to a reduction in chest wall compliance as lung compliance was constant. FRC declined from 32.3 +/- 1.7 ml/kg at 3 days to 25.1 +/- 1.5 ml/kg at 2 weeks, then fell to 21.4 +/- 1.2 ml/kg by 8 weeks. Specific pulmonary conductance (conductance/FRC) during mid-inspiration and mid-expiration did not change with age (0.195 +/- 0.012 and 0.194 +/- 0.019 L x sec(-1) x cmH2O(-1) x L(-1)-FRC, respectively). Breathing frequency, and weight-adjusted tidal volume and minute ventilation declined after birth until 4 weeks after which they did not change. This study has shown that, using basic methodology, serial assessments of respiratory function can be obtained in sedated lambs from soon after birth. The age-related increase seen in pulmonary diffusing capacity is due to increases in both Dm and Vc, which are consistent with continuing alveolarisation. Our data on age-related changes in pulmonary function and volumes provide a reference for future studies on the effect of altered prenatal lung development on postnatal lung function in sheep.