Changes in myocardial blood volume a wide range of coronary driving pressures: Role of capillaries beyond the autoregulatory range

D. E. Le, A. R. Jayaweera, K. Wei, M. P. Coggins, J. R. Lindner, S. Kaul

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    34 Scopus citations


    Objective: To determine whether, when the vasomotor capacity of the coronary arterioles is exhausted at rest, myocardial blood volume decreases in order to maintain a normal capillary hydrostatic pressure, even at the expense of myocardial axygen delivery. Methods: 18 dogs were studied. In group 1 (n = 9), coronary driving pressure (CDP) was reduced by 10-80 mm Hg below normal by a stenosis; in group 2 (n = 9), it was increased 20-80 mm Hg above baseline by increasing aortic pressure with phenylephrine. Myocardial contrast echocardiography (MCE) was undertaken to measure the myocardial blood volume fraction and myocardial blood flow (MBF). Results: In group 1 dogs, as CDP was reduced, both coronary blood flow (CBF) and MBF decreased. Myocardial blood volume fraction also decreased and myocardial vascular resistance increased, while coronary sinus PO2 decreased. In group 2 dogs, as CDP was increased, epicardial CBF increased but MBF remained unchanged because of a decrease in myocardial blood volume fraction. Myocardial vascular resistance decreased, however, implying the presence of coronary arteriovenous shunting, which was supported by a progressive increase in the coronary sinus PO 2. Conclusions: Wnen arteriolar tone is exhausted so that CBF becomes dependent on CDP, myocardial blood volume decreases in order ta maintain a constant capillary hydrostatic pressure, which takes precedence over myocardial oxygen delivery. These novel findings implicate capillaries in the regulation of CBF beyond the autoregulatory range.

    Original languageEnglish (US)
    Pages (from-to)1199-1205
    Number of pages7
    Issue number10
    StatePublished - Oct 1 2004


    ASJC Scopus subject areas

    • Cardiology and Cardiovascular Medicine

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