Usefulness of the 6-minute walk test as a screening test for pulmonary arterial enlargement in COPD

Abstract

Purpose: Pulmonary hypertension and exercise-induced oxygen desaturation (EID) influence acute exacerbation of COPD. Computed tomography (CT)-detected pulmonary artery (PA) enlargement is independently associated with acute COPD exacerbations. Associations between PA to aorta (PA:A) ratio and EID in patients with COPD have not been reported. We hypothesized that the PA:A ratio correlated with EID and that results of the 6-minute walk test (6MWT) would be useful for predicting the risk associated with PA:A >1. Patients and methods: We retrospectively measured lung function, 6MWT, emphysema area, and PA enlargement on CT in 64 patients with COPD. The patients were classified into groups with PA:A ≤1 and >1. Receiver-operating characteristic curves were used to determine the threshold values with the best cutoff points to predict patients with PA:A >1. Results: The PA:A >1 group had lower forced expiratory volume in 1 second (FEV 1 ), forced vital capacity (FVC), FEV 1 :FVC ratio, diffusion capacity of lung carbon monoxide, 6MW distance, and baseline peripheral oxygen saturation (SpO 2 ), lowest SpO 2 , highest modified Borg scale results, percentage low-attenuation area, and history of acute COPD exacerbations ≤1 year, and worse BODE (Body mass index, airflow Obstruction, Dyspnea, and Exercise) index results ( P <0.05). Predicted PA:A >1 was determined for SpO 2 during 6MWT (best cutoff point 89%, area under the curve 0.94, 95% confidence interval 0.88–1). SpO 2 <90% during 6MWT showed a sensitivity of 93.1, specificity of 94.3, positive predictive value of 93.1, negative predictive value of 94.3, positive likelihood ratio of 16.2, and negative likelihood ratio of 0.07. Conclusion: Lowest SpO 2 during 6MWT may predict CT-measured PA:A, and lowest SpO 2 <89% during 6MWT is excellent for detecting pulmonary hypertension in COPD. Keywords: 6-minute walk test, chronic obstructive pulmonary disease, exercise-induced oxygen desaturation, pulmonary artery