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Development of pulmonary vascular response to oxygen
F C Morin1, E A Egan, W Ferguson
1Department of Pediatrics, University at Buffalo, New York.
The American Journal of Physiology
|March 1, 1988
Summary
Fetal lambs under 101 days gestation show no pulmonary circulation response to increased oxygen. Near-term lambs, however, exhibit a significant increase in pulmonary blood flow with higher oxygen levels, mimicking postnatal breathing.
Area of Science:
- Physiology
- Developmental Biology
- Cardiovascular Research
Background:
- The transition from fetal to neonatal circulation involves significant changes in pulmonary blood flow.
- Pulmonary vascular resistance must decrease dramatically at birth to accommodate air breathing.
- The role of oxygen in mediating these circulatory changes in the fetus is not fully understood.
Purpose of the Study:
- To investigate the responsiveness of the fetal lamb pulmonary circulation to increased oxygen tension at different gestational ages.
- To determine the gestational timing of pulmonary vascular adaptation to hyperoxia.
- To assess whether oxygen alone can induce the postnatal increase in pulmonary blood flow in late-term fetuses.
Main Methods:
- Studied unanesthetized fetal lambs (94-146 days gestation) in a hyperbaric chamber.
- Administered 100% oxygen at 3 atmospheres absolute pressure to the ewe.
- Measured fetal arterial oxygen tension (PaO2) and the proportion of right ventricular output to the lungs.
- Quantified pulmonary blood flow in a subset of near-term lambs.
Main Results:
- Very immature lambs (94-101 days) showed no change in pulmonary blood flow distribution despite a large increase in PaO2.
- Near-term lambs (132-146 days) demonstrated a significant increase in pulmonary blood flow distribution (8% to 59%) with elevated PaO2.
- Pulmonary blood flow in near-term lambs increased 8.8-fold (34 to 298 ml.kg fetal wt-1.min-1) in response to hyperoxia.
Conclusions:
- The fetal lamb pulmonary circulation is immature and unresponsive to oxygen-induced vasodilation before 101 days of gestation.
- By late gestation, the pulmonary vasculature is capable of responding to increased oxygen tension.
- Increased oxygen tension alone can trigger the substantial rise in pulmonary blood flow observed at birth, suggesting a key role in circulatory transition.