title: Impact of volume-dependent alveolar diffusing capacity on exhaled nitric oxide concentration.
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.
authors.affiliation: Department of Chemical and Biochemical Engineering and Materials Science, University of California, Irvine, 92697-2575, USA.
authors.forename: N M
authors.initials: NM
authors.lastname: Tsoukias
authors.forename: S C
authors.initials: SC
authors.lastname: George
mesh_terms: D001698:Biomedical Engineering; D006801:Humans; D008176:Lung Volume Measurements; D008954:Models, Biological; D009569:Nitric Oxide / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000502:physiology*; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*
chemical_list: D009569:Nitric Oxide