Development of pulmonary vascular response to oxygen.
The ability of the pulmonary circulation of the fetal lamb to respond to a rise in oxygen tension was studied from 94 to 146 days of gestation. The unanesthetized ewe breathed room air at normal atmospheric pressure, followed by 100% oxygen at three atmospheres absolute pressure in a hyperbaric chamber. In eleven near-term lambs (132 to 146 days of gestation), fetal arterial oxygen tension (PaO2) increased from 25 +/- 1 to 55 +/- 6 Torr (mean +/- SE), which increased the proportion of right ventricular output distributed to the fetal lungs from 8 +/- 1 to 59 +/- 5%. In five very immature lambs (94 to 101 days of gestation), fetal PaO2 increased from 27 +/- 1 to 174 +/- 70 Torr, but the proportion of right ventricular output distributed to the lung did not change, 8 +/- 1 to 9 +/- 1%. In five of the near-term lambs, pulmonary blood flow was measured. It increased from 34 +/- 3 to 298 +/- 35 ml.kg fetal wt-1.min-1, an 8.8-fold increase. We conclude that the pulmonary circulation of the fetal lamb does not respond to an increase in oxygen tension before 101 days of gestation; however, near term an increase in oxygen tension alone can induce the entire increase in pulmonary blood flow that normally occurs after the onset of breathing at birth.
Morin
F C
FC
Department of Pediatrics, University at Buffalo, New York.
Egan
E A
EA
Ferguson
W
W
Lundgren
C E
CE
D000818:Animals; D001775:Blood Circulation; D005260:Female; D005333:Fetus / Q000502:physiology*; D006931:Hyperbaric Oxygenation; D008168:Lung / Q000196:embryology*; D010100:Oxygen / Q000097:blood / Q000494:pharmacology*; D010313:Partial Pressure; D011247:Pregnancy; D011652:Pulmonary Circulation / Q000187:drug effects*; D012756:Sheep / Q000196:embryology
D010100:Oxygen