CT-defined emphysema in COPD patients and risk for change in desaturation status in 6-min walk test.

Background: Emphysema and exercise induced desaturation (EID) are both related to poorer COPD prognosis. More knowledge of associations between emphysema and desaturation is needed for more efficient disease management.

Research Question: Is emphysema a risk factor for both new and repeated desaturation, and is emphysema of more or less importance than other known risk factors?

Methods: 283 COPD patients completed a 6-min walk test (6MWT) at baseline and one year later in the Bergen COPD cohort study 2006-2011. Degree of emphysema was assessed as percent of low attenuation areas (%LAA) under -950 Hounsfield units using high-resolution computed tomography at baseline. We performed multinomial logistic regression analysis, receiver operating curves (ROC) and area under the curve (AUC) estimations. Dominance analysis was used to rank emphysema and risk factors in terms of importance.

Results: A one percent increase in %LAA increases the relative risk (RR) of new desaturation by 10 % (RR 1.1 (95%CI 1.1, 1.2)) and for repeated desaturation by 20 % (RR 1.2 (95%CI 1.1, 1.3)). Compared with other important desaturation risk factors, %LAA ranked as number one in the dominance analysis, accounting for 50 % and 37 % of the predicted variance for new and repeated desaturators, respectively. FEV% predicted accounted for 9 % and 24 %, and resting SpO accounted for 22 % and 21 % for new and repeated desaturation.

Conclusion: Emphysema increases the risk of developing and repeatedly experiencing EID. Emphysema seems to be a more important risk factor for desaturation than FEV% predicted and resting saturation.