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Related Experiment Videos

Convection- and diffusion-dependent ventilation maldistribution in normal subjects.

A B Crawford, M Makowska, M Paiva

    Journal of Applied Physiology (Bethesda, Md. : 1985)
    |September 1, 1985
    PubMed
    Summary

    Multiple-breath nitrogen washouts reveal that the normalized slope of the alveolar plateau (Sn) increases due to diffusion-independent mechanisms after five breaths. This increase may serve as a sensitive index for convection-dependent inhomogeneity in the lungs.

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    Area of Science:

    • Pulmonary Physiology
    • Respiratory Mechanics

    Background:

    • Multiple-breath washouts (MBW) are used to assess lung ventilation distribution.
    • Understanding the factors influencing gas washout, such as diffusion and convection, is crucial for interpreting MBW data.

    Purpose of the Study:

    • To investigate the mechanisms driving changes in the normalized slope of the alveolar plateau (Sn) during multiple-breath nitrogen washouts (MBNW).
    • To differentiate between diffusion-dependent and convection-dependent components of lung inhomogeneity.

    Main Methods:

    • Performed multiple-breath nitrogen washouts (MBNW) in six healthy subjects with tidal volumes of 1 liter at 8-16 breaths/min.
    • Calculated Sn, Bohr dead space (VDB), Fowler dead space analog (V50), and normalized slope of phase II (S2) for each breath.
    • Conducted helium and sulfur hexafluoride washouts in four subjects to assess tracer-specific behavior.

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    Main Results:

    • Sn, VDB, and V50 increased progressively during MBNW, with Sn increasing by approximately 290% from the first to the 25th breath.
    • The normalized slope of phase II (S2) remained unchanged initially and decreased after the sixth breath.
    • The increase in Sn after the fifth breath was diffusion-independent, suggesting it reflects convection-dependent inhomogeneity (CDI).

    Conclusions:

    • The increase in Sn after five breaths during MBNW is a diffusion-independent index of convection-dependent inhomogeneity (CDI).
    • CDI may represent ventilation inequality in larger lung units.
    • The initial Sn component likely reflects diffusion-dependent mechanisms, possibly involving convection-diffusion interactions in the lung periphery.