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Microvascular hemodynamics during systemic hemodilution and hemoconcentration.

H H Lipowsky, J C Firrell

    The American Journal of Physiology
    |June 1, 1986
    PubMed
    Summary

    Red blood cell flux in microvessels is optimized at a systemic hematocrit of 28-46%. Changes in hematocrit affect red blood cell delivery and utilization, influencing oxygen transport efficiency.

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    Area of Science:

    • Physiology
    • Biophysics
    • Microcirculation

    Background:

    • Understanding red blood cell (RBC) behavior in microcirculation is crucial for oxygen delivery.
    • Systemic hematocrit (Hctsys) significantly impacts blood rheology and microvascular function.

    Purpose of the Study:

    • To investigate the effects of hemodilution and hemoconcentration on RBC velocity, microvessel hematocrit (Hctmicro), and volumetric flux (QRBC).
    • To determine the optimal Hctsys range for maximizing QRBC and efficient oxygen delivery in the mesenteric microvasculature.

    Main Methods:

    • Measurements of intravascular pressure, RBC velocity, and Hctmicro in cat mesenteric arterioles and venules.
    • Systemic hemodilution (using cell-free plasma) and hemoconcentration (using packed cells) were induced.
    • Calculation of QRBC from microvessel bulk flow and Hctmicro across a range of Hctsys (5-67%).

    Main Results:

    • Hemodilution showed heterogeneous responses in QRBC, with smaller arterioles potentially enhancing oxygen delivery.
    • Averaged across all vessels, dilution decreased QRBC, but altered Hctmicro indicated more efficient RBC utilization.
    • Hemoconcentration also decreased QRBC, suggesting QRBC is maximized between 28% and 46% Hctsys.
    • Regional vascular resistance showed a plateau with increasing Hctsys, attributed to reduced vascular hindrance and stable capillary blood viscosity.

    Conclusions:

    • The study identified an optimal systemic hematocrit range for maximizing red blood cell flux and potentially oxygen delivery.
    • Microvascular adaptations, including RBC redistribution, help maintain blood viscosity and function across varying hematocrits.
    • Findings contribute to understanding the complex interplay between hematocrit, microcirculation, and oxygen transport.

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