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(Chest. 2002;121:1092-1098.)
© 2002 American College of Chest Physicians

Power of Outcome Measurements to Detect Clinically Significant Changes in Pulmonary Rehabilitation of Patients With COPD*

Juan Pablo de Torres, MD; Victor Pinto-Plata, MD; Edward Ingenito, MD; Peter Bagley, MD, FCCP; Anthony Gray, MD, FCCP; Robert Berger, MD and Bartolome Celli, MD, FCCP

* From the Pulmonary and Critical Care Division (Drs. de Torres, Pinto-Plata, and Celli), St. Elizabeth’s Medical Center, Boston; Pulmonary and Critical Care Division (Dr. Ingenito), Brigham and Women’s Hospital, Boston; Pulmonary and Critical Care Division (Dr. Bagley), Lahey Clinic, Boston; and Pulmonary and Critical Care Division (Dr. Gray), University of Massachusetts Medical Center, Boston; and Harvard School of Medicine (Dr. Berger), Boston, MA.

Correspondence to: Bartolome Celli, MD, FCCP, St. Elizabeth’s Medical Center, Pulmonary and Critical Care Division, 736 Cambridge St, Boston, MA 02135-2997; e-mail: bcelli{at}semc.org


   Abstract
TOP
 Abstract
Materials and Methods
 Results
 Discussion
 References
 
Study objectives: Several validated instruments are used to measure outcomes, such as exercise performance, dyspnea, and health-related quality of life after pulmonary rehabilitation (PR) in patients with COPD. However, no study has simultaneously compared the responsiveness of the most frequently used outcome measurements after PR. We designed this study to investigate the capacity of several of the most frequently used outcome measurements to detect changes after PR in a population of patients with severe COPD who qualified for lung volume reduction surgery.

Design, patients, and interventions: We evaluated 37 patients with severe COPD (FEV1 < 40%) before and after 6 to 8 weeks of outpatient PR. The following frequently used tools were evaluated: the 6-min walk distance (6MWD); functional dyspnea with the Medical Research Council (MRC) scale; baseline and transitional dyspnea index (BDI/TDI); resting and 6MWD visual analog scale (VAS); quality of life with a generic tool (the Short Form-36 [SF-36]); and two disease-specific tools, the Chronic Respiratory Disease Questionnaire (CRQ) and the St. George’s Respiratory Questionnaire (SGRQ).

Results: After PR, mean ± SD 6MWD increased in 33 of 37 patients (89%), from 285 ± 97 to 343 ± 92 m (p = 0.009). Improvements were seen also in the MRC scale in 23 of 37 patients (62%; from 2.27 ± 0.8 to 1.86 ± 0.6; p = 0.01); in CRQ dyspnea in 25 of 37 patients (67%; from 3.25 ± 0.9 to 3.90 ± 1.4; p = 0.02); in CRQ mastery in 22 of 37 patients (60%; from 4.37 ± 1.4 to 5.14 ± 1.3; p = 0.01); and in BDI/TDI functional in 24 of 37 patients (64%; from 1.4 ± 0.8 to 0.7 ± 1.1; p = 0.002). There were smaller improvements in the SGRQ in 18 of 37 patients (48%) and in the SF-36 in 19 of 37 patients (51%), but they were not statistically significant. There were good correlations between the dyspnea components of all the tools. The 6MWD change did not correlate with the changes in the other outcomes. Clinically significant changes in the values for those outcome tools were detected in > 50% of patients for the BDI/TDI, 29% of patients for the MRC scale, in 37% of patients for the 6MWD, in 48% of patients for the VAS at peak exercise, in > 50% of patients for the CRQ, and in 40% of patients for the SGRQ.

Conclusions: We conclude that the VAS peak exercise, BDI/TDI, and CRQ adequately reflect the beneficial effects of PR. The 6MWD evaluates a unique domain not related to quality of life. Due to their simplicity and sensitivity, VAS at peak exercise, 6MWD, and CRQ may be the best practical tools to evaluate responsiveness to PR.

Key Words: COPD • pulmonary rehabilitation • quality of life

Pulmonary rehabilitation (PR) is an important therapy in the management of patients with symptomatic COPD, because it improves the perception of dyspnea, exercise tolerance, and health-related quality of life (HRQOL).1 2 3 4 5 6 7 8 9 10 The effectiveness of PR has been evaluated using many different outcome tools. Functional dyspnea improvement has been documented using the Medical Research Council (MRC) scale11 and the baseline and transitional dyspnea index (BDI/TDI),12 whereas exercise dyspnea has been shown to improve using the visual analog scale (VAS)13 and the Borg scale.14 Increased exercise tolerance has been most frequently documented using the 6-min walk distance (6MWD).15 HRQOL has been evaluated with disease-specific tools (the St. George’s Respiratory Questionnaire [SGRQ]16 and the Chronic Respiratory Disease Questionnaire [CRQ]17 ) and also with more generic questionnaires, such as the Short Form-36 (SF-36).18 Although all these tools are useful, they are time consuming and require training to be used and interpreted correctly. The health-care practitioner could be helped by well-validated information providing a guide to help select the simplest tools that adequately capture the changes induced by PR.

To date, only two studies19 20 have compared the power of the most frequently used outcome tools to detect different domains in cohorts of patients with COPD. However, the patients in those studies were not followed up prospectively, and the ability of the different tools to better detect changes induced by PR remains unknown.

Only four studies 21 22 23 24 have prospectively compared different HRQOL questionnaires after PR. In one study,21 the discriminative power of the questionnaires was not the primary outcome, and the information provided does not allow a conclusion about the value of either tool. One study22 supports the validity of one general (SF-36) and one specific (CRQ) HRQOL questionnaire to detect changes after PR. The other two studies23 24 showed that disease-specific HRQOL questionnaires are substitutive in detecting changes after PR. However, none of these studies simultaneously evaluated the change in dyspnea or the correlation between HRQOL and other outcomes such as the 6MWD. Therefore, it is entirely possible that one or two of the tools may encompass the information provided by the others and that time may be spent duplicating unnecessary information.

We designed this study to investigate the capacity of several of the most frequently used outcome measurements to detect changes after PR, in a population of severe COPD patients who qualified for lung volume reduction surgery (LVRS). The tools evaluated included the following: dyspnea (VAS at rest and end of exercise, MRC scale, BDI/TDI), exercise performance (6MWD), and HRQOL (SF-36, SGRQ, and CRQ).


   Materials and Methods
TOP
 Abstract
 Materials and Methods
Results
 Discussion
 References
 
Study Population
The population consisted of the first 37 consecutive patients with severe COPD selected for LVRS at seven hospitals in Massachusetts as part of the Overholt/Blue Cross/Blue Shield Emphysema Surgical Trial. The human research committee at all institutions approved the study. All patients signed the informed consent. In summary, the study population consists of all the patients participating in an ongoing trial comparing LVRS and standard medical treatment. All patients completed 6 to 8 weeks of PR as a requisite to be randomized either to surgical or medical treatment. To be included in the study, the patients had to be < 75 years old, with a medical history, physical examination, and radiologic imaging that confirmed the clinical diagnosis of emphysema. FEV1 had to be < 40%, total lung capacity had to be > 125%, and residual volume had to be > 175% of the predicted values. The patients were receiving maximal medical treatment defined as some form of ß-agonist or anticholinergic therapy, and could have received a trial of an additional agent: theophylline, oral prednisone (dose < 15 mg/d), or inhaled steroids. All patients had to be able to complete the questionnaires and walk.

PR
Members of the Overholt/Blue Cross/Blue Shield Emphysema Surgical Trial coordinating committee trained the staff at all of the rehabilitation centers, including the adoption of a uniform exercise protocol and certification in outcome testing. Quality was ensured by a central coordinating officer.

The PR program consisted of 24 sessions over 6 to 8 weeks. The sessions included warm-up and cool-down exercises, and lower-extremity exercise using a combination of treadmill, bicycle ergometer, free walking, or restorator to achieve 30 min of continuous exercise; upper-extremity exercise for a minimum of 15 min; diaphragmatic breathing and controlled coughing exercises; as well as a review of the proper use of inhalers. At-home exercise programs were prescribed, to be completed on days when the program was not attended. Patients were asked to keep a diary of activities, which was reviewed by the rehabilitation coordinator at each visit.

Outcome Tools
All the patients were assessed before and immediately after the PR program using the following protocol.

Pulmonary function:
Spirometry was performed according to American Thoracic Society (ATS) guidelines. FEV1, FVC, and FEV1/FVC were calculated according to ATS criteria.25

Dyspnea:
Dyspnea was assessed using the following tools. For exercise, the VAS,13 with anchors of "no shortness of breath" and "extreme shortness of breath," was used. This test was evaluated at rest and at the end of 6MWD. Functional dyspnea was evaluated with two tools: the MRC scale modified by the ATS,11 which consists of 5 increasing scores from 0 to 4 with anchors of "no breathlessness except with strenuous exercise" and "breathless when dressing or undressing" (there is no report of the change in MRC score that is associated with a clinically significant improvement or deterioration); and the BDI/TDI developed by Mahler et al,12 which includes three domains (functional impairment, magnitude of task, and magnitude of effort) that are graded from - 3 to + 3, where - 1 to - 3 signifies deterioration, 0 signifies no change, and 1 to 3 signifies improvement (the change in 1 U has been thought to imply clinical significance).

Exercise Endurance:
This was evaluated using the modified 6MWD protocol.15 In short, patients were instructed to walk at their fastest pace and to cover the longest possible distance over 6 min. Oxygen saturation was continuously monitored, supplementary oxygen was supplied to keep oxygen saturation > 88%, and the equipment was carried by the technician. This could imply that different oxygen flows were used for the tests. Every 2 min, the patients were encouraged using the phrase "you are doing well, keep on going." Once familiar with the instructions, and after two practice sessions, the two tests were completed in a 50-m corridor with a 30-min rest between tests. The longest walk was taken to represent the value for that visit. It has been shown that there is no significant difference after two tests.26 The following variables were recorded: meters walked, heart and respiratory rates, BP, oxygen flow, and lowest oxygen saturation.

HRQOL:
HRQOL was evaluated using three questionnaires. Two are disease-specific questionnaires, the SGRQ16 and the CRQ. The SGRQ consists of 50 items with 76 weighted responses and three component scores: symptoms, activities, and impacts (psychosocial dysfunction). A total score is calculated from all three components, with zero indicating no health impairment and 100 representing maximum impairment. A change in score of 4 U has been identified as clinically significant.

The CRQ17 is comprised of four scores: dyspnea, fatigue, emotional function, and mastery measured on a 7-point scale, with a score of 7 indicating no health impairment. The dyspnea component of the questionnaire is individualized to five activities that cause dyspnea and are assessed in order of importance and severity by the patient. A change of 0.5 U has been identified as the minimum clinically significant change. The other HRQOL tool was a generic one, the SF-36,18 27 which consists of 36 questions that cover nine health concepts: physical function, social function, role function, role function emotional, mental health, bodily pain, vitality, general health perceptions, and health transitions. For all measures of the nine health components, scores were transformed linearly to scales of 0 to 100, with 0 indicating maximal impairment and 100 indicating the minimal impairment. The magnitude of change in the score of the SF-36 that reflects a clinically significant change has not been determined.

Statistical Analysis
Values are presented as mean ± SD unless otherwise stated. For all tools, the values obtained before and after PR were compared using a paired t test. The number of patients that improved in each outcome measurement tool was expressed in absolute number and as percentage of the total. Pearson’s correlation coefficients (r) were used to examine the degree of association among dyspnea tools, dyspnea and 6MWD, HRQOL tools, 6MWD and HRQOL tools, and dyspnea tools and dyspnea components of the HRQOL tools. For all tests, a p < 0.05 was considered significant. The statistics were completed using a standard statistical package (GBStat; Dynamic Microsystems; Silver Spring, MD).


   Results
TOP
 Abstract
 Materials and Methods
 Results
Discussion
 References
 
All 37 patients enrolled completed the 8 weeks of PR. Their demographic and physiologic characteristics are shown in Table 1 . Both genders were represented. The patients had severe COPD and were severely hyperinflated.


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  		Table 1. Demographic and Physiologic Data of the 37 Patients Participating in the Study*

 
The pre-PR and post-PR values for the tools are shown in Table 2 . There were statistical significant improvements in MRC scale (p = 0.018), 6MWD (p = 0.0096), VAS at peak exercise (p < 0.0001), CRQ dyspnea (p = 0.02), CRQ mastery (p = 0.016), BDI/TDI magnitude of effort (p = 0.0006), BDI/TDI magnitude of task (p < 0.0001), and BDI/TDI functional status (p = 0.002). No statistical significant improvements were observed in CRQ emotional function, CRQ fatigue and in all of the domains of the SGRQ, and the SF-36.


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  		Table 2. Outcome Measurement Tools*

 
Clinically significant changes were seen in > 50% of the patients (BDI/TDI, - 1 U; CRQ, + 0.5 U; and VAS peak exercise, - 1 U). Fewer than 50% of the patients had clinically significant changes in SGRQ (- 4%), VAS at rest (- 1 U), 6MWD (+ 54 m), and MRC scale (- 1).

The difference in symptoms response to PR in the domain of disease-specific questionnaires (CRQ and SGRQ) is shown in Figure 1 . The CRQ dyspnea tool was more sensitive to detect clinically significant changes (0.5 points) that the SGRQ (4 U), even though the latter did have a mean change of close to 4 U.



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  		Figure 1. Effect of PR on selected health status outcome. The number of patients and the degree of improvement were greater in the CRQ dyspnea domain (upper panel) than in the SGRQ symptoms domain (lower panel). Improvements in CRQ are reflected as positive changes, whereas, by design, improvements in SGRQ are reflected as negative changes.

 
A significant and strong correlation was seen among the dyspnea tools (MRC, VAS, CRQ dyspnea, and BDI/TDI) as well as among the HRQOL tools (CRQ, SGRQ, and SF-36) before PR. The 6MWD did not correlate with any of the other outcome tools.

We also correlated the magnitude of variation ({Delta}) of the outcomes in 6MWD, MRC scale, VAS, CRQ dyspnea and mastery, and BDI/TDI magnitude of effort. The correlation between the changes is shown in Table 3 . {Delta}MRC correlated with {Delta}VAS (r = 0.35, p < 0.05) and {Delta}BDI/TDI magnitude of effort (r = 0.37, p < 0.05). {Delta}CRQ dyspnea and mastery correlated with {Delta}SGRQ impact (r = - 0.43 and r = - 0.61, respectively), and {Delta}SGRQ total correlated with {Delta}CRQ dyspnea (r = - 0.41, p < 0.05), fatigue (r = -0.44, p < 0.05), and mastery (r = - 0.41, p < 0.05). The change in the 6MWD did not correlate with any of the changes in the other outcome tools.


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  		Table 3. Correlation Between the Changes in Outcome Measurements Tools

 

   Discussion
TOP
 Abstract
 Materials and Methods
 Results
 Discussion
References
 
This prospective study was designed to evaluate the responsiveness of the most commonly used outcome measurement tools for PR in patients with COPD, and had two major findings: (1) the clinically significant improvements in BDI/TDI, VAS at peak exercise, and the CRQ capture the beneficial effects of PR in most of the patients; and (2) the 6MWD in a unique way evaluates exercise capacity, and its change is not adequately reflected by the others tools.

PR in patients with COPD provides benefits in the perception of dyspnea, exercise tolerance, and HRQOL.1 2 3 4 5 6 7 8 9 10 28 However, the widespread availability of different outcomes measurement tools makes very difficult any direct comparison of many of these trials. Furthermore, the clinician or health-care professional involved in PR finds difficult and often times confusing the actual selection of tools to simply and effectively evaluate the effect of the programs.

Four studies have compared the common tools used to assess HRQOL.21 22 23 24 The investigators in the first study21 showed that the CRQ was more sensitive than the SGRQ for detecting responses to PR. However, the main goal of the study was to stratify patients with the MRC scale and determine their response to PR, and not to determine the capacity of these tools to detect changes. Harper et al22 showed that both generic (SF-36 and EuroQol) and disease-specific (CRQ and SGRQ) questionnaires were reliable instruments over time. They also showed that generic questionnaires reflect better other health problems than disease-specific questionnaires and that the CRQ was more sensitive than the SGRQ. Singh et al23 compared three disease-specific and two generic HRQOL questionnaires, showing that all disease-specific questionnaire findings improve after PR, but the CRQ was the most sensitive. Finally Griffiths et al24 documented the changes observed in HRQOL 1 year after PR, but did not evaluate the different responsiveness of the instruments used, perhaps due to the design of the study, which was to evaluate the effect of PR in utilization of health-care resources.

There are two studies19 20 that compared evaluation of dyspnea and HRQOL in a cross-sectional way in a cohort of patients with COPD. The first study19 showed that clinical dyspnea ratings (MRC scale, baseline dyspnea index), activity of the SGRQ, and dyspnea of the CRQ performed identically in patients with COPD. The second study20 also demonstrated that there were no substantial differences in the evaluatory properties of the CRQ and the SGRQ. However, the tools were not tested prospectively; therefore, the discriminative power of the tools to detect changes over time remains unknown.

The unique feature of our study is that it compares several of the existing assessment tools using PR as the intervention in a cohort of patients with severe COPD. It is generally agreed that dyspnea is the most disabling symptom of these patients; therefore, improvement in this outcome is a very important goal of therapy. All of the studies that evaluated dyspnea as an outcome showed a significant improvement in perceived dyspnea in treated patients irrespective of the tool used.1 2 3 4 5 6 7 8 9 We also observed an improvement in dyspnea that was reflected by all the dyspnea tools. Our findings are consistent with those of Hajiro et al,19 who showed that these different tools performed similarly in a cross-sectional way. Because any one of these tools (VAS with exercise, MRC scale, dyspnea component of the CRQ, and BDI/TDI) can be used to detect the changes in dyspnea, their ease of administration could help define their use. The magnitude of change in the different tools is also important because that magnitude may indicate the clinical impact of the intervention. In this regard, the dyspnea scales behaved similarly, changing approximately by the same percentage from baseline. The MRC scale and VAS are simpler and easier to determine, and therefore could be recommended as first-line tools to evaluate dyspnea.

The 6MWD is frequently used to assess the functional status and exercise capacity of patients with COPD because it is inexpensive, reliable, safe, and valid.29 There are many studies2 30 that have shown the beneficial effects of PR on exercise tolerance measured as the walked distance. The mean improvement for our patients was 65 m, a value that is compatible with previous studies30 and higher than the 54 m thought to represent the minimal distance that has to improve for the COPD patients to notice a difference in their functional status.31 The improvement in this severe group of patients does highlight the practical use of this test. However, only 29% of the patients improved > 54 m in our group.

It is possible that the 6MWD could have been represented by any of the other tools and thereby be not necessary in the routine evaluation of the effectiveness of PR. The results of our study suggest otherwise: the change in the distance walked did not correlate with the changes in any other outcome. We postulate that the 6MWD evaluates a unique domain. Because walking is one of the simplest and most common activities, it is an integrative useful test to assess the physical, psychological, and emotional capabilities of patients, and is not adequately assessed by any of the other tools here reported. In addition, the 6MWD has been shown to be a good predictor of survival in patients with COPD,32 congestive heart failure,33 and primary pulmonary hypertension.34 Indeed, in this last group, it proved to have a better predictive power than symptomlimited cardiopulmonary exercise testing. Therefore, we believe the 6MWD should be recommended as a tool that provides independent information regarding a patient’s functional status.

Several studies8 35 have shown that PR significantly improves the reported quality of life in patients with symptomatic COPD. However, few studies have directly compared the discriminative power of generic and disease-specific HRQOL tools as primary outcomes in a prospective way.21 22 23 24 All these studies have shown that disease-specific questionnaires perform better than the generic ones. In addition, the studies23 24 have also shown that the CRQ may be more sensitive than the SGRQ.

There is only one study20 that specifically compared the discriminative power of the different disease-specific quality-of-life questionnaires in a cross-sectional design. The authors compared the discriminative power of the SGRQ, the CRQ, and the Breathing Problems Questionnaire. The SGRQ and the CRQ had similar discriminative power. Our results showed a correlation among the tools when tested cross-sectionally at baseline (dyspnea: VAS, BDI/TDI, MRC, and CRQ dyspnea; HRQOL: CRQ and SGRQ) but they differed when tested prospectively. The SF-36 questionnaire was less sensible to detect any change after PR.

The CRQ questionnaire showed a statistically significant (p < 0.05) and a clinically significant (> 0.5 points) improvement in three of its components, respectively. Furthermore, > 50% of the patients showed improvement in three of the components (dyspnea, fatigue, and mastery). The mean change observed in the SGRQ almost reached the level of clinical significance (- 4 points), but it only changed in < 50% of the patients. However, given the large distribution of changes in the response, it did not reach statistical significance. Perhaps with a larger number of patients, the value would have reached statistical significance. Taken as a whole, the results suggest that the CRQ is a more sensitive tool to assess the changes resulting from pulmonary rehabilitation. The differences in sensitivity may be due to the way in which the questionnaires were developed. Whereas the SGRQ and SF-36 are designed to provide a categorical response to many questions (yes-or-no format), the CRQ allows the symptoms to be expressed in a graduated scale. Because most patients with severe symptoms may only perceive subtle changes, a graded scale may better detect those changes. In addition, the CRQ allows the patient to grade the dyspnea in a group of self-selected activities, thereby magnifying those areas that may be missed in questionnaires that include a fixed set of questions.

Our study findings are compatible with the article published by Singh et al,23 who prospectively compared three different disease-specific questionnaires (SGRQ, CRQ, and the Breathing Problems Questionnaire) and two generic (global quality of life and an activity checklist), showing that all three disease-specific questionnaires improved after PR, but the CRQ was the most sensitive.

We found interesting that those parameters that improved in > 50% of the patients were the same (MRC, 6MWD, CRQ dyspnea, fatigue and mastery, BDI/TDI, and VAS). These results indicate that these tools can evaluate the changes resulting from PR over time, and that they provide similar information.

One possible criticism of our study is the strict selection criteria of our patients. They all had severe COPD (FEV1 < 40% predicted) and were highly motivated because they were included in a surgical trial. However, the study purpose was better served by having a homogeneous population, highly compliant and with clearly defined goals. In addition, if changes were detected in a population with this severe degree of airflow limitation, we could speculate that the same outcomes could show even larger responses in patients with less severe disease. The study could also be criticized because of the relatively small number of patients. However, the total number is similar to the majority of published studies.19 20 21 In addition, every patient recruited completed all aspects of the study, and there were no dropouts or missing values.

In conclusion, we found that in highly motivated patients with severe COPD, the 6MWD, MRC scale, BDI/TDI, VAS exercise, and the CRQ adequately reflect the beneficial effects of PR. In addition, we have observed that the 6MWD evaluate a unique domain. The MRC scale, BDI/TDI, and CRQ dyspnea evaluate similar domains. We propose a simple testing scheme for patients undergoing PR that should include the 6MWD, the CRQ, and the VAS with exercise. Our study suggests that these are the best practical tools to evaluate dyspnea, exercise tolerance, and HRQOL, and their response to a PR program.


   Footnotes
 
Abbreviations: ATS = American Thoracic Society; BDI/TDI = baseline and transitional dyspnea index; CRQ = Chronic Respiratory Disease Questionnaire; HRQOL = health-related quality of life; LVRS = lung volume reduction surgery; MRC = Medical Research Council; 6MWD = 6-min walk distance; PR = pulmonary rehabilitation; SF-36 = Short-Form-36; SGRQ = St. George’s Respiratory Questionnaire; VAS = visual analog scale

Supported in part by the Overholt/Blue Cross/Blue Shield Emphysema Surgical Trial, The Thoracic Foundation, and Biovascular, Inc.

Received for publication July 19, 2001. Accepted for publication October 23, 2001.


   References
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 Abstract
 Materials and Methods
 Results
 Discussion
 References
 

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