Elsevier

Respiratory Medicine

Volume 94, Issue 1, January 2000, Pages 28-37
Respiratory Medicine

Regular Article
Importance of adjusting carbon monoxide diffusing capacity (DLCO) and carbon monoxide transfer coefficient (K CO) for alveolar volume

https://doi.org/10.1053/rmed.1999.0740Get rights and content
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Abstract

The volume dependence of single breath carbon monoxide diffusing capacity (DLCO) and carbon monoxide transfer coefficient (K CO) was determined in 24 healthy subjects. The change in DLCO [fraction of DLCO measured at total lung capacity (TLC)] to change in alveolar volume [fraction of alveolar volume (VA) at TLC] closely fitted a simple linear regression and matched a theoretical model. As VAdecreased, DLCO fell linearly and K CO increased as expected from the relation of DLCO to VA. The equations for adjustment of predicted DLCO and K CO for alveolar volume are:DLCO/DLCOtlc=0·58+0·42 VA/VAtlcKCO/KCOtlc=0·42+0·58/(VA/VAtlc)DLCO and K CO were evaluated in 2313 patients. Subgroups of patients with asthma, emphysema, extrapulmonary lung disease, interstitial lung disease and lung resection were identified. Unadjusted DLCO and K CO percent predicted values showed large differences and much variability, so can be misleading. As expected, K CO and DLCO percent predicted values adjusted for alveolar volume were nearly identical. Subgroups have characteristic patterns of V A and unadjusted and adjusted DLCO and K CO. Changes in DLCO and K CO with alveolar volume are relevant for accurate interpretation of diffusion in patients with low lung volumes. Adjusting predictedDL CO and K CO for alveolar volume provides a better assessment of lung function.

Keywords

asthma
DLCO
DLCO/V A
emphysema
interstitial lung disease
K CO
lung volume
normals
sarcoidosis.

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Correspondence should be addressed to: Douglas C. Johnson, M.D., Director, Pulmonary Function Laboratory, Pulmonary and Critical Care Unit, Massachusetts General Hospital, Boston, MA 02114, U.S.A. Fax: +1 617 726 6878; E-mail: [email protected]