Pulmonary pressure-flow relationships in the fetal lamb during in utero ventilation

D. L. Reid, K. L. Thornburg

    Research output: Contribution to journalArticle

    21 Scopus citations

    Abstract

    Pressure-flow relationships in the ventilated lung have not been previously determined in undelivered fetal sheep. Therefore we studied 11 late-gestation chronically prepared fetal sheep during positive-pressure ventilation with different gas mixtures to determine the roles of mechanical distension and blood gas tensions on pressure-flow relationships in the lung. Ventilation with 3% O2-7% CO2 produced a substantial fall in pulmonary vascular resistance even though arterial blood gases were not changed. Increases in pulmonary arterial PO2 during ventilation were associated with falls in pulmonary vascular resistance beyond that measured during mechanical distension. Decreases in pulmonary arterial PCO2 and associated increases in pH were also associated with falls in pulmonary vascular resistance. Pulmonary blood flow ceased at a pulmonary arterial pressure that exceeded left atrial pressure, indicating that left atrial pressure does not represent the true downstream component of driving pressure through the pulmonary vascular bed. The slope of the driving pressure-flow relationship in the normal mature fetal lamb was therefore different from the ratio of pulmonary arterial pressure to pulmonary arterial flow. We conclude that mechanical ventilation, increased PO2 and decreased PCO2, and/or increased pH has an important influence on the fall in pulmonary vascular resistance elicited by positive pressure in utero ventilation of the fetal lamb and that the downstream driving pressure for pulmonary blood flow exceeds left atrial pressure.

    Original languageEnglish (US)
    Pages (from-to)1630-1636
    Number of pages7
    JournalJournal of Applied Physiology
    Volume69
    Issue number5
    DOIs
    StatePublished - Jan 1 1990

    Keywords

    • birth
    • fetus
    • pulmonary blood flow
    • pulmonary vascular resistance

    ASJC Scopus subject areas

    • Physiology
    • Physiology (medical)

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