Our aim was to determine the effects of low birth weight on ventilatory responses to progressive hypoxia and hypercapnia during early postnatal life. Seven low-birth-weight (2.7 ± 0.3 kg) and five normal-birth-weight (4.8 ± 0.2 kg) lambs, all born at term, underwent weekly rebreathing tests during wakefulness while arterial PO2, PCO2, and pH were measured. Hypoxic ventilatory responsiveness (HOVR; percent increase in ventilation when arterial PO2 fell to 60% of resting values) increased in normal lambs from 86.6 ± 7.1% at week 1 to 227.4 ± 24.9% at week 6. In low-birth-weight lambs, HOVR was not significantly different at week 1 (60.1 ± 18.7%) from that of normal lambs but did not increase with postnatal age (56.6 ± 19.3% at week 6). HOVR of all lambs at 6 wk was significantly correlated with birth weight (r2 = 0.8). Hypercapnic ventilatory responsiveness (gradient of ventilation vs. arterial PCO2) did not change with age and was not significantly different between groups [84.7 ± 7.5 (low-birth-weight lambs) vs. 89.4 ± 6.6 ml · min-1 · kg-1 · mmHg-1 (normal lambs)]. We conclude that intrauterine conditions that impair fetal growth lead to the failure of HOVR to increase with age.
- growth restriction
- small for gestational age