Development of ventilatory responsiveness to progressive hypoxia and hypercapnia in low-birth-weight lambs.
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 605 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.
Department of Physiology, Monash University, Clayton, Victoria, Australia. t.moss@med.monash.edu.au
T J
TJ
Moss
M G
MG
Davey
G J
GJ
McCrabb
R
R
Harding
D000375:Aging / Q000502:physiology; D000818:Animals; D001724:Birth Weight / Q000502:physiology*; D001784:Blood Gas Analysis; D001835:Body Weight / Q000502:physiology; D006128:Growth / Q000502:physiology; D006935:Hypercapnia / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D015656:Respiratory Mechanics / Q000502:physiology*; D012756:Sheep