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Changes in the pulmonary circulation during birth-related events.
D F Teitel1, H S Iwamoto, A M Rudolph
1Cardiovascular Research Institute, University of California, San Francisco 94143.
Pediatric Research
|April 1, 1990
Summary
Fetal lung ventilation dramatically reduces pulmonary vascular resistance, with oxygenation further decreasing it. However, individual fetal responses to ventilation varied significantly, with no clear explanation found.
Area of Science:
- Physiology
- Neonatal physiology
- Cardiovascular research
Background:
- Pulmonary vascular resistance (PVR) must decrease dramatically at birth for gas exchange.
- The transition from fetal to neonatal circulation involves complex physiological changes.
Purpose of the Study:
- To quantify the roles of fetal lung ventilation, oxygenation, and umbilical cord occlusion in reducing PVR.
- To investigate variability in fetal circulatory responses to these transition events.
Main Methods:
- Studied 16 instrumented near-term fetal sheep in utero.
- Sequentially applied ventilation, oxygenation, and umbilical cord occlusion.
- Measured pulmonary blood flow (radionuclide-labeled microspheres) and vascular pressures to calculate PVR.
Main Results:
- Ventilation alone significantly reduced PVR (to 34% of control) by increasing pulmonary blood flow.
- Oxygenation further decreased PVR (to 10% of control).
- Umbilical cord occlusion had no additional effect.
- Observed two distinct groups of fetuses regarding their blood flow response to ventilation, with no identifiable cause for the difference.
Conclusions:
- Fetal lung ventilation and oxygenation are critical for the rapid decrease in pulmonary vascular resistance at birth.
- Significant inter-individual variability exists in fetal circulatory responses to transition stimuli.
- Further research is needed to understand the mechanisms behind this observed variability.