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  • Title: Impact of volume-dependent alveolar diffusing capacity on exhaled nitric oxide concentration.
    Author: Tsoukias NM, George SC.
    Journal: Ann Biomed Eng; 2001 Sep; 29(9):731-9. PubMed ID: 11599581.
    Abstract:
    Exhaled endogenous nitric oxide (NO) holds promise as a potential biomarker of pulmonary inflammation. Previous experimental and theoretical work has concluded that the alveolar concentration approaches a constant steady state value at end exhalation due to both a constant maximum flux or release of NO (J(max,alv)) and a constant diffusing capacity (D(NO,alv)) in the alveolar region. We have recently demonstrated that D(NO,alv) is not constant, but increases with alveolar volume (VA) given by the following average relationship: D(NO,alv) =48*VA(2/3) ml/min/mmHg (where VA is expressed in liters, STPD). We investigated the potential impact of a variable D(NO,alv) on exhaled concentration by incorporating the volume dependence into the currently accepted two-compartment model for NO exchange dynamics. Our results suggest that the mechanism underlying the plateau in exhaled concentration is a constant ratio J(max,alv)/D(NO,alv) This constant ratio requires a volume dependence of J(max,alv) similar to D(NO,alv), and is likely due to a decreasing alveolar surface area during exhalation.
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