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Diminished stroke volume during inspiration: a reverse thoracic pump.

C O Olsen, G S Tyson, G W Maier

    Circulation
    |September 1, 1985
    PubMed
    Summary
    This summary is machine-generated.

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    During breathing, stroke volume decreases due to reduced effective left ventricular ejection pressure, not preload changes. This finding highlights the reverse thoracic pump mechanism impacting cardiac function.

    Area of Science:

    • Cardiovascular Physiology
    • Respiratory Mechanics
    • Hemodynamics

    Background:

    • Inspiratory maneuvers can decrease stroke volume, a phenomenon partly attributed to autonomic reflexes.
    • Understanding the precise mechanisms behind inspiratory stroke volume changes is crucial for comprehending cardiopulmonary interactions.

    Purpose of the Study:

    • To investigate the determinants of the inspiratory decline in left ventricular stroke volume in conscious dogs.
    • To differentiate the roles of autonomic reflexes, preload, afterload, and ventricular geometry in this phenomenon.

    Main Methods:

    • Utilized sonomicrometry to measure left and right ventricular dimensions in conscious dogs.
    • Measured pressures (left ventricular, right ventricular, intrapleural) and aortic blood flow.

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  • Controlled heart rate via pacing and modulated autonomic activity with propranolol and atropine.

    • Main Results:

    • Despite controlling for heart rate and autonomic influences, stroke volume decreased by approximately 10% during inspiration.
    • Inspiratory increases in right ventricular volume led to septal shifting and altered left ventricular geometry, but left ventricular end-diastolic volume remained unchanged.
    • The fall in stroke volume correlated best with a decline in left ventricular ejection pressure referenced to atmospheric pressure.

    Conclusions:

    • Autonomic reflexes are not the sole cause of the inspiratory stroke volume decline.
    • Changes in preload and afterload were not significant contributors.
    • A decrease in effective left ventricular ejection pressure, driven by the reverse thoracic pump mechanism, is hypothesized as the primary cause of the inspiratory fall in stroke volume.