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Importance of Appropriately Adjusting Diffusing Capacity of the Lung for Carbon Monoxide and Diffusing Capacity of the Lung for Carbon Monoxide/Alveolar Volume Ratio for Lung Volume

Spaulding Rehabilitation Hospital, Boston, MA

Correspondence to: Douglas C. Johnson, MD, Spaulding Rehabilitation Hospital, 125 Nashua St, Boston, MA 02114; e-mail: djohnson5{at}partners.org

To the Editor:

I thank Traynor et al (May 2005)¹ for providing data showing the importance of appropriately adjusting the diffusing capacity of the lung for carbon monoxide (DLCO) and DLCO/alveolar volume (VA) ratio for measured lung volume.

DLCO falls and DLCO/VA ratio increases with smaller VA,²³ so an unadjusted DLCO underestimates diffusion and an unadjusted DLCO/VA markedly overestimates diffusion at low lung volumes. A method for adjusting DLCO and DLCO/VA ratio for lung volume, which fits the theoretical and empiric data well,² multiplies predicted DLCO by (0.58 + 0.42*VAfr), and predicted DLCO/VA ratio by (0.42 + 0.58/VAfr), where Vafr is the measured VA/predicted VA ratio. DACO (ie, DLCO adjusted for VA) and KACO (DLCO/VA or KCO adjusted for VA) have the same percentage of the predicted value.

At baseline, the patients of Traynor et al¹ with refractory systemic lupus erythematosus had a DLCO of 54% predicted (12% were >80% predicted), a DLCO/VA ratio of 84% predicted (53% were >80% predicted), and DACO and KACO values of 62% predicted (12% were >80% predicted). Two patients increased DLCO by 27% and 18%, but decreased DLCO/VA ratio by 41% and 54% during sustained remissions, with DACO increasing by 15% and 10%. Very different interpretations of lung function occur using percent predicted values for DLCO or DLCO/VA ratio. DACO and KACO provide better assessments of diffusion capacity.

References

1. Traynor, AE, Corbridge, TC, Eagan, AE, et al (2005) Prevalence and reversibility of pulmonary dysfunction in refractory systemic lupus: improvement correlates with disease remission following hematopoietic stem cell transplantation. Chest 127,1680-1689[Abstract/Free Full Text]
2. Johnson, DC Importance of adjusting carbon monoxide diffusing capacity (DLCO) and carbon monoxide transfer coefficient (KCO) for alveolar lung volume. Respir Med 2000;94,28-37[CrossRef][ISI][Medline]
3. MacIntyre, N, Crapo, R, Viegi, G, et al Standardization of the single breath determination of carbon monoxide uptake in the lung. Eur Respir J 2005;26,720-735[Abstract/Free Full Text]

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