Postnatal changes in ventilatory responsiveness to progressive
hypoxia and hypercapnia in low birthweight lambs.
Moss, T. J., M. G. Davey, G. J. McCrabb, and R. Harding.
Fetal and Neonatal Research Unit, Department of Physiology, Monash
University, Clayton 3168, AUSTRALIA
APStracts 3:0255A, 1996.
Our aim was to determine the effects of low birthweight on ventilatory
responses to progressive hypoxia and hypercapnia during early
postnatal life. Seven low birthweight (2.7 +/- 0.3 kg) and 5 normal
birthweight (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; %
increase in ventilation when Pao2 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 birthweight lambs HOVR was not significantly
different at week 1 (60.1 +/- 18.7%) to that of normal lambs, but did
not increase with postnatal age (56.6 +/- 19.3% at week 6). HOVR of
all lambs at 6 weeks was significantly correlated with birthweight
(r2=0.8). Hypercapnic ventilatory responsiveness (gradient of
ventilation vs Paco2) did not change with age and was not
significantly different between groups (low birthweight lambs, 84.7
+/- 7.5 vs normal lambs, 89.4 +/- 6.6 ml/min/kg/mmHg). We conclude
that intrauterine conditions that impair fetal growth lead to the
failure of HOVR to increase with age.
Received 11 December 1995; accepted in final form 20 May 1996.
APS Manuscript Number A1285-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96