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Fetal and Neonatal Research Unit, Department of Physiology, Monash University, Clayton, Victoria 3168, Australia
Received 11 December 1995; accepted in final form 20 May 1996.
Moss, T. J., M. G. Davey, G. J. McCrabb, and R. Harding.
Development of ventilatory responsiveness to progressive hypoxia and hypercapnia in low-birth-weight lambs. J. Appl.
Physiol. 81(4): 1555-1561, 1996.
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.
newborn; growth restriction; small for gestational age; rebreathing
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