The continuum of physiological impairment during treadmill walking in patients with mild-to-moderate COPD: patient characterization phase of a randomized clinical trial.

Denis E O'Donnell,Denis E O'Donnell,Richard Casaburi,Richard Casaburi,Richard Casaburi,Heather A Paden,Frank C Albers,Katherine A Webb,Katherine A Webb,On Behalf Of The 205.440 Investigators ,Janos Porszasz,Ahmar Iqbal,François Maltais,François Maltais,Qiqi Deng

doi:10.1371/journal.pone.0096574

Abstract

BackgroundTo have a better understanding of the mechanisms of exercise limitation in mild-to-moderate chronic obstructive pulmonary disease (COPD), we compared detailed respiratory physiology in patients with COPD and healthy age- and sex-matched controls.MethodsData were collected during the pre-treatment, patient characterization phase of a multicenter, randomized, double-blind, crossover study. Patients with COPD met Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1 or 2 spirometric criteria, were symptomatic, and had evidence of gas trapping during exercise. All participants completed pulmonary function and symptom-limited incremental treadmill exercise tests.ResultsChronic activity-related dyspnea measured by Baseline Dyspnea Index was similarly increased in patients with GOLD 1 (n = 41) and 2 (n = 63) COPD compared with controls (n = 104). Plethysmographic lung volumes were increased and lung diffusing capacity was decreased in both GOLD groups. Peak oxygen uptake and work rate were reduced in both GOLD groups compared with controls (p<0.001). Submaximal ventilation, dyspnea, and leg discomfort ratings were higher for a given work rate in both GOLD groups compared with controls. Resting inspiratory capacity, peak ventilation, and tidal volume were reduced in patients with GOLD 2 COPD compared with patients with GOLD 1 COPD and controls (p<0.001).ConclusionsLower exercise tolerance in patients with GOLD 1 and 2 COPD compared with controls was explained by greater mechanical abnormalities, greater ventilatory requirements, and increased subjective discomfort. Lower resting inspiratory capacity in patients with GOLD 2 COPD was associated with greater mechanical constraints and lower peak ventilation compared with patients with GOLD 1 COPD and controls.Trial RegistrationClinicalTrials.gov: NCT01072396

Highlights

The majority of patients with chronic obstructive pulmonary disease (COPD) worldwide have mild-to-moderate disease severity [1], yet these patients are less extensively studied than those with severe disease
It remains to be determined if mechanical and gas exchange derangements exist during walking in milder COPD, and if these are similar in magnitude and direction to those previously documented during cycle ergometry in this population
Participants Participants were enrolled into the study between March 16, 2010 and August 1, 2011, the first patient entered the treatment phase on April 14, 2010 and the last completed on November 29, 2011

Summary

Introduction

The majority of patients with chronic obstructive pulmonary disease (COPD) worldwide have mild-to-moderate disease severity [1], yet these patients are less extensively studied than those with severe disease. Weight-bearing treadmill exercise is fundamentally different from weight-supported cycling in terms of the extent of metabolic loading, acid-base and pulmonary gas exchange abnormalities, and locomotor muscle recruitment pattern [20,21,22]. It remains to be determined if mechanical and gas exchange derangements exist during walking in milder COPD, and if these are similar in magnitude and direction to those previously documented during cycle ergometry in this population. To have a better understanding of the mechanisms of exercise limitation in mild-to-moderate chronic obstructive pulmonary disease (COPD), we compared detailed respiratory physiology in patients with COPD and healthy age- and sex-matched controls

Methods

Results

Conclusion