POSTNATAL-DEVELOPMENT OF RESPIRATORY-FUNCTION IN LAMBS STUDIED SERIALLY BETWEEN BIRTH AND 8 WEEKS

We have quantified developmental changes in major aspects of respirato ry function in 12 pentobarbitone-sedated lambs by making repeated meas urements during the first 8 postnatal weeks, between term birth and po st-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 c apacity measured at a lung inflation pressure of 30 cmH(2)O decreased from 74.4 +/- 3.2 ml/kg at 3 days to 47.2 +/- 2.9 ml/kg at 8 weeks. St atic respiratory system compliance, measured between FRC and TLC fell rapidly during the first 3 weeks, then remained unchanged; the early p ostnatal 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) dur ing mid-inspiration and mid-expiration did not change with age (0.195 +/- 0.012 and 0.194 +/- 0.019 L.sec(-1).cmH(2)O(-1).L-1-FRC, respectiv ely). Breathing frequency, and weight-adjusted tidal volume and minute ventilation declined after birth until 4 weeks after which they did n ot change. This study has shown that, using basic methodology, serial assessments of respiratory function can be obtained in sedated lambs f rom soon after birth. The age-related increase seen in pulmonary diffu sing capacity is due to increases in both Dm and Vc, which are consist ent with continuing alveolarisation. Our data on age-related changes i n pulmonary function and volumes provide a reference for future studie s on the effect of altered prenatal lung development on postnatal lung function in sheep. (C) 1998 Elsevier Science B.V. All rights reserved .