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


RESULTS
Chronic 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).


CONCLUSIONS
Lower 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.


BACKGROUND
ClinicalTrials.gov: NCT01072396.
Queen's University & Kingston General Hospital, Kingston, Ontario, Canada.
Denis E
DE
O'Donnell
Centre de Recherche, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, Canada.
François
F
Maltais
Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America.
Janos
J
Porszasz
Queen's University & Kingston General Hospital, Kingston, Ontario, Canada.
Katherine A
KA
Webb
Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, Connecticut, United States of America.
Frank C
FC
Albers
Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, Connecticut, United States of America.
Qiqi
Q
Deng
Pfizer Inc, New York, New York, United States of America.
Ahmar
A
Iqbal
Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, Connecticut, United States of America.
Heather A
HA
Paden
Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America.
Richard
R
Casaburi
D000328:Adult; D000368:Aged; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004417:Dyspnea / Q000209:etiology* / Q000503:physiopathology; D005080:Exercise Test / Q000009:adverse effects*; D017079:Exercise Tolerance; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology*; D006801:Humans; D007866:Leg / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications* / Q000503:physiopathology