Determining the Role of Dynamic Hyperinflation in Patients with Severe Chronic Obstructive Pulmonary Disease

BACKGROUND: Dynamic hyperinflation due to increased respiratory frequency during exercise is associated with limitations in exercise capacity in patients with moderately severe chronic obstructive pulmonary disease (COPD). OBJECTIVES: The present study assessed whether the manually paced tachypnea (MPT) test, sitting at rest, induces dynamic hyperinflation correlating with exercise capacity in patients with very severe COPD. METHODS: Dynamic hyperinflation was induced by the MPT test, using a breathing frequency of 40/min for 1 min. Dynamic hyperinflation was defined as a 'change' in inspiratory capacity (IC) before and directly after the MPT test. At baseline, static hyperinflation by body plethysmography was measured, as well as the 6-min walking test and spirometry. RESULTS: We studied 74 patients with severe COPD (age 59 ± 9 years, FEV1 28 ± 10% predicted). All patients tolerated the MPT test well. It induced a significant decrease in IC: -0.65 ± 0.33 liters, p < 0.001, correlating with the 6-min walking distance (rho = -0.246, p = 0.034). Static hyperinflation [IC/total lung capacity (TLC)] at baseline correlated stronger with the 6-min walking distance (r = 0.582, p < 0.001). Multiple regression analysis showed that IC/TLC, but not dynamic hyperinflation, was the only independent predictor of walking distance. CONCLUSIONS: In patients with very severe COPD, dynamic hyperinflation measurement by the MPT test is feasible and contributes less importantly to exercise performance than static hyperinflation.