Determinants of exercise capacity in chronic obstructive pulmonary disease

Abstract

Background: COPD commonly results in progressive exertional intolerance. Apart from cardiac and peripheral muscular limitations, respiratory muscle failure adds to the development of exercise intolerance, but its pathophysiology remains understood incompletely. Therefore, we investigated respiratory muscle pump function determinants of exercise capacity in COPD patients.

Methods: 61 COPD patients (65 [58-74] years, 26 [21-31] kg/m², median [quartile1-3]) were prospectively examined. Functional parameters of ventilation, gas exchange at rest and during exercise, as well as volitional and non-volitional respiratory muscle strength metrics during in- and expiration were measured. All parameters were correlated with 6-minute walk distance (6MWD). Significantly correlated parameters where then used in multivariable linear regression, adjusted for age, gender and BMI, to further identify determinants of exercise capacity.

Results: A linear regression model (adjusted r²=0.725) identified forced vital capacity (FVC) and transdiaphragmatic twitch pressure following cortical magnetic stimulation of the phrenic nerves (TwPdi) as the strongest independent determinants of 6MWD (table 1).

Conclusion: This study is the first to identify cortical twPdi as an independent determinant of exercise intolerance in COPD, reflecting involvement of not only peripheral respiratory muscle pathology but also central nervous system structures in the pathophysiology of respiratory failure and exercise intolerance.