Chest
Volume 141, Issue 3, March 2012, Pages 753-762
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Original Research
COPD
Decline of Resting Inspiratory Capacity in COPD: The Impact on Breathing Pattern, Dyspnea, and Ventilatory Capacity During Exercise

https://doi.org/10.1378/chest.11-0787Get rights and content

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 (

e) and tidal volume (Vt) decreased, whereas an inflection or plateau of the Vt response occurred at a progressively lower
e (P < .0005), similar percentage of peak
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.

Section snippets

Materials and Methods

The data from two randomized, double-blind, placebo-controlled clinical trials that evaluated the effects of daily tiotropium on exercise tolerance, hyperinflation, and dyspnea in patients with COPD were retrospectively combined for this analysis.7, 8 There is no overlap between this independent analysis of the pretreatment data and previous analyses of the same data set.7, 8, 9, 10 The Queen's University and Affiliated Teaching Hospitals Research Ethics Board approved the use of these data and

Subjects

Characteristics of the 427 evaluable subjects are shown in Table 1. Age, height, BMI, and COPD duration were similar across the FEV1 quartiles. There was a larger percentage of current smokers in Q1 than in the other three quartiles. Pulmonary function data showed that lung hyperinflation worsened progressively as disease severity increased. Peak incremental cycle work rate and oxygen consumption (

o2) also decreased progressively from Q1 to Q4.

Physiologic Responses to Symptom-Limited CWR Exercise

Measurements at the peak of CWR exercise are

Discussion

The novel findings of this study were as follows: (1) the progressive erosion of resting IC with worsening airflow obstruction and hyperinflation was associated with the development of an increasingly shallow, rapid breathing pattern and worsening dyspnea at progressively lower levels of ventilation during exercise, and (2) despite significant interquartile differences in resting airflow obstruction, lung hyperinflation, and ventilatory capacity, exertional dyspnea intensity consistently

Conclusions

The resting IC importantly influences ventilatory capacity, breathing pattern responses, and the evolution of exertional dyspnea across the range of disease severity in patients with COPD who hyperinflate during exercise. Progressive reduction of the resting IC with increasing disease severity was associated with the appearance of critical constraints on Vt expansion and attendant increase in dyspnea at a progressively lower ventilation during exercise. Regardless of baseline differences in

Acknowledgments

Author contributions: Dr O'Donnell had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Dr O'Donnell: contributed to the study design and conduct as principal investigator of the original multicenter trials, the original idea for the current analysis and interpretation of the results, and the writing of the manuscript.

Dr Guenette: contributed to the data analysis and preparation for presentation and writing

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    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).

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