Diaphragmatic excursion correlates with exercise capacity and dynamic hyperinflation in COPD patients

Background Although the pathophysiological mechanisms involved in the development of dyspnoea and poor exercise tolerance in patients with COPD are complex, dynamic lung hyperinflation (DLH) plays a central role. Diaphragmatic excursions can be measured by ultrasonography (US) with high intra- and interobserver reliability. The objective of this study was to evaluate the effect of diaphragmatic excursions as assessed by US on exercise tolerance and DLH in patients with COPD. Methods Patients with COPD (n=20) and age-matched control subjects (n=20) underwent US, which was used to determine the maximum level of diaphragmatic excursion (DE max ). Ventilation parameters, including the change in inspiratory capacity (ΔIC), were measured in the subjects during cardiopulmonary exercise testing (CPET). We examined the correlations between DE max and the ventilation parameters. Results The DE max of patients with COPD was significantly lower than that of the controls (45.0±12.8 mm versus 64.6±6.3 mm, respectively; p<0.01). The perception of peak dyspnoea (Borg scale) was significantly negatively correlated with DE max in patients with COPD. During CPET, oxygen uptake/weight ( V ′ O 2 / W ) and minute ventilation ( V ′ E ) were significantly positively correlated with DE max , while V ′ E / V ′ O 2 and V ′ E /carbon dioxide output ( V ′ CO 2 ) were significantly negatively correlated with DE max in patients with COPD. DE max was also significantly positively correlated with ΔIC, reflecting DLH, and with V ′ O 2 / W , reflecting exercise capacity. Conclusion Reduced mobility of the diaphragm was related to decreased exercise capacity and increased dyspnoea due to dynamic lung hyperinflation in COPD patients.