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Mechanisms of Dyspnea during Cycle Exercise in Symptomatic Patients with GOLD Stage I Chronic Obstructive Pulmonary Disease

¹ Respiratory Investigation Unit, Department of Medicine, and ² Department of Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada

Correspondence and requests for reprints should be addressed to Dr. Denis O'Donnell, M.D., F.R.C.P.C., 102 Stuart Street, Kingston, ON, K7L 2V6 Canada. E-mail: odonnell{at}queensu.ca

Rationale: Smokers with a relatively preserved FEV₁ may experience dyspnea and activity limitation but little is known about underlying mechanisms.

Objectives: To examine ventilatory constraints during exercise in symptomatic smokers with GOLD (Global Initiative for Chronic Obstructive Lung Disease) stage I chronic obstructive lung disease (COPD) so as to uncover potential mechanisms of dyspnea and exercise curtailment.

Methods: We compared resting pulmonary function and ventilatory responses (breathing pattern, operating lung volumes, pulmonary gas exchange) with incremental cycle exercise as well as Borg scale ratings of dyspnea intensity in 21 patients (post-bronchodilator FEV₁, 91 ± 7% predicted, and FEV₁/FVC, 60 ± 6%; mean ± SD) with significant breathlessness and 21 healthy age- and sex-matched control subjects with normal spirometry.

Measurements and Main Results: In patients with COPD compared with control subjects, peak oxygen consumption and power output were significantly reduced by more than 20% and dyspnea ratings were higher for a given work rate and ventilation (P < 0.05). Compared with the control group, the COPD group had evidence of extensive small airway dysfunction with increased ventilatory requirements during exercise, likely on the basis of greater ventilation/perfusion abnormalities. Changes in end-expiratory lung volume during exercise were greater in COPD than in health (0.54 ± 0.34 vs. 0.06 ± 0.32 L, respectively; P < 0.05) and breathing pattern was correspondingly more shallow and rapid. Across groups, dyspnea intensity increased as ventilation expressed as a percentage of capacity increased (P < 0.0005) and as inspiratory reserve volume decreased (P < 0.0005).

Conclusions: Exertional dyspnea in symptomatic patients with mild COPD is associated with the combined deleterious effects of higher ventilatory demand and abnormal dynamic ventilatory mechanics, both of which are potentially amenable to treatment.

Key Words: mild chronic obstructive pulmonary disease • respiratory mechanics • ventilation • dynamic hyperinflation

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Patients with mild chronic obstructive pulmonary disease (COPD) and a relatively preserved FEV1 may report poor perceived health status. The link between ventilatory impairment, symptom development, and activity limitation has never been systematically explored in mild GOLD stage I COPD. What This Study Adds to the Field Symptomatic patients with GOLD I COPD can have significant pathophysiologic abnormalities that lead to clinically important dyspnea and exercise intolerance. Dyspnea correlated with increased ventilation and dynamic lung hyperinflation during exercise.

 

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