Asynchronous Thoraco-abdominal Motion Contributes to Decreased 6-Minute Walk Test in Patients With COPD

BACKGROUND: Abnormal thoraco-abdominal motion may contribute to exercise limitation in patients with COPD. The current study aimed to assess how the thoraco-abdominal asynchrony in COPD patients correlates with exercise performance during the 6-minute walk test (6MWT). METHODS: Eighty-eight COPD subjects (40 moderate and 48 severe) and 14 healthy controls were evaluated at rest and during the 6MWT for the magnitude of rib cage and abdominal motion and asynchrony between the two (phase angle) with respiratory inductive plethysmography. RESULTS: Compared to healthy control subjects, subjects with COPD had similar magnitude of rib cage and abdominal motion, but greater asynchrony at rest. During the 6MWT, subjects with COPD showed decreased rib cage motion and increased asynchrony. Rib cage excursion at 3 min after the beginning of the 6MWT was an independent predictor for the 6MWT distance (P < .001), in addition to age, percent of predicted FEV1, and residual volume/total lung capacity. There was no correlation between rib cage excursion at 3 min and St George's Respiratory Questionnaire score. CONCLUSIONS: Thoraco-abdominal asynchrony worsens early during 6MWT in subjects with moderate and severe COPD, and rib cage excursion at 3 min predicts poor walking capability. A pulmonary rehabilitation strategy devised to improve rib cage excursion may help improve exercise tolerance.