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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 FREE TO VIEW

Douglas C. Johnson, MD
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Spaulding Rehabilitation Hospital, Boston, MA

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



Chest. 2006;129(4):1113. doi:10.1378/chest.129.4.1113-a
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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.

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.Chest127,1680-1689
 
Johnson, DC Importance of adjusting carbon monoxide diffusing capacity (Dlco) and carbon monoxide transfer coefficient (KCO) for alveolar lung volume.Respir Med2000;94,28-37
 
MacIntyre, N, Crapo, R, Viegi, G, et al Standardization of the single breath determination of carbon monoxide uptake in the lung.Eur Respir J2005;26,720-735
 

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References

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.Chest127,1680-1689
 
Johnson, DC Importance of adjusting carbon monoxide diffusing capacity (Dlco) and carbon monoxide transfer coefficient (KCO) for alveolar lung volume.Respir Med2000;94,28-37
 
MacIntyre, N, Crapo, R, Viegi, G, et al Standardization of the single breath determination of carbon monoxide uptake in the lung.Eur Respir J2005;26,720-735
 
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