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Predictors of Success in Pulmonary Rehabilitation for Patients With Interstitial Lung Disease FREE TO VIEW

Fahad Al-Ghimlas, MD; David C. Todd, MD
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Affiliations: Drs. Al-Ghimlas and Todd are affiliated with McMaster University. Drs. Al-Ghimlas and Todd contributed equally to the drafting and critical revision of the manuscript.

Correspondence to: Fahad Al-Ghimlas, MD, St. Joseph's Healthcare Hamilton, 50 Charlton Ave East, Room T2123-1, Hamilton, ON, Canada L8N 4A6; e-mail: dr_alghimlas@yahoo.com


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


© 2009 American College of Chest Physicians


Chest. 2009;136(4):1183-1184. doi:10.1378/chest.09-1164
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We read with interest the recent study in CHEST (February 2009) by Ferreira et al,1 which provides further evidence supporting the beneficial effects of pulmonary rehabilitation (PR) in patients with interstitial lung diseases (ILDs). The aim of this observational study was also to identify patient characteristics that are predictors of benefit for patients receiving PR.

Although nine potential variables were identified a priori, baseline 6-min walk test distance (6MWD) was the only predictor of benefit. Specifically, the results of the study by Ferreira et al1 indicate that a lower 6MWD at baseline is a predictor of greater improvement in 6MWD following PR. Caution is needed when assessing predictors of success for any intervention. Participants with a very low baseline 6MWD are more likely to have an increase in walking distance even without any actual benefit from the intervention since they are unlikely to or cannot do worse. Similarly, participants with a higher baseline 6MWD will be more apt to experience the opposite effect because they are starting at the “ceiling” of the measured outcome and are not expected to improve any further beyond their baseline values. This phenomenon, often referred to as the regression to the mean2 might result in misleading conclusions about the mean change and predictors of success when the values of participants are at the extremes of the range of an outcome.

A careful visual examination of the scatterplot graph in Figure 1 of the article by Ferreira et al1 supports this concept. It is established that “outliers” that are located at either extreme of the range of values will have an appreciable effect in changing the slope of the best-fitted regression line.3 In Figure 1, there are outlier values for patients with very low baseline 6MWDs (ie, < 100 m) who were among the participants with the largest change in 6MWD following PR. Similarly, at the other extreme there are participants with very high baseline 6MWDs (ie, approaching 600 m) who had little to no change following PR, likely due to a “ceiling effect.” If these outlier values were omitted from the model, we hypothesize that the best-fitted regression line would most likely be close to a horizontal line, indicating no overall relationship.

More prospective studies are needed to assess the predictors of benefit for PR in patients with ILD (and COPD) that are hypothesis driven as opposed to data driven. Unfortunately, this study does not provide strong enough evidence to support prescribing PR for patients with ILD based on their characteristics such as baseline values for 6MWD.

Financial/nonfinancial disclosures: The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Ferreira A, Garvey C, Connors GL, et al. Pulmonary rehabilitation in interstitial lung disease: benefits and predictors of response. Chest. 2009;135:442-447. [PubMed] [CrossRef]
 
Streiner DL, Norman GR. Health measurement scales: a practical guide to their development and use. 2003;3rd ed Oxford, UK Oxford University Press
 
Kleinbaum DG, Kupper LL, Muller KE, et al. Applied regression analysis and other multivariable methods. 2007;4th edition Pacific Grove, CA Duxbury Press
 

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References

Ferreira A, Garvey C, Connors GL, et al. Pulmonary rehabilitation in interstitial lung disease: benefits and predictors of response. Chest. 2009;135:442-447. [PubMed] [CrossRef]
 
Streiner DL, Norman GR. Health measurement scales: a practical guide to their development and use. 2003;3rd ed Oxford, UK Oxford University Press
 
Kleinbaum DG, Kupper LL, Muller KE, et al. Applied regression analysis and other multivariable methods. 2007;4th edition Pacific Grove, CA Duxbury Press
 
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