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Original Research: COPD |

Decline of Resting Inspiratory Capacity in COPDInspiratory Capacity Predicts Ventilatory Capacity: The Impact on Breathing Pattern, Dyspnea, and Ventilatory Capacity During Exercise

Denis E. O’Donnell, MD, FCCP; Jordan A. Guenette, PhD; François Maltais, MD; Katherine A. Webb, MSc
Author and Funding Information

From the Respiratory Investigation Unit (Drs O’Donnell and Guenette and Ms Webb), Department of Medicine, Queen’s University and Kingston General Hospital, Kingston, ON; and Centre de Recherche (Dr Maltais), Institut Universitaire de cardiologie et de pneumologie de Québec, Université Laval, Québec City, QC, Canada.

Correspondence to: Denis E. O’Donnell, MD, FCCP, 102 Stuart St, Kingston, ON, K7L 2V6, Canada; e-mail: odonnell@queensu.ca


Funding/Support: Funding received from Boehringer-Ingelheim GmbH (to Dr Guenette).

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2012 American College of Chest Physicians


Chest. 2012;141(3):753-762. doi:10.1378/chest.11-0787
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Background:  To better understand the interrelationships among disease severity, inspiratory capacity (IC), breathing pattern, and dyspnea, we studied responses to symptom-limited cycle exercise in a large cohort with COPD.

Methods:  Analysis was conducted on data from two previously published replicate clinical trials in 427 hyperinflated patients with COPD. Patients were divided into disease severity quartiles based on FEV1 % predicted. Spirometry, plethysmographic lung volumes, and physiologic and perceptual responses to constant work rate (CWR) cycle exercise at 75% of the peak incremental work rate were compared.

Results:  Age, body size, and COPD duration were similar across quartiles. As the FEV1 quartile worsened (mean, 62%, 49%, 39%, and 27% predicted), functional residual capacity increased (144%, 151%, 164%, and 185% predicted), IC decreased (86%, 81%, 69%, and 60% predicted), and peak incremental cycle work rate decreased (66%, 55%, 50%, and 44% predicted); CWR endurance time was 9.7, 9.3, 8.2, and 7.3 min, respectively. During CWR exercise, as FEV1 quartile worsened, peak minute ventilation (V˙ e) and tidal volume (Vt) decreased, whereas an inflection or plateau of the Vt response occurred at a progressively lower V˙ e (P < .0005), similar percentage of peak V˙ e (82%-86%), and similar Vt/IC ratio (73%-77%). Dyspnea intensity at this inflection point was also similar across quartiles (3.1-3.7 Borg units) but accelerated steeply to intolerable levels thereafter.

Conclusion:  Progressive reduction of the resting IC with increasing disease severity was associated with the appearance of critical constraints on Vt expansion and a sharp increase in dyspnea to intolerable levels at a progressively lower ventilation during exercise.

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