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Individuals with chronic obstructive pulmonary disease (COPD) have been shown to benefit from participation in pulmonary rehabilitation (PR) programs that include exercise training and education. Purpose: To examine the relationship between improvements in 6 minute walk distance and perceived quality of life in individuals with COPD following completion of a PR program. Methods: The records of 139 individuals completing a PR program (3 times a week for 8 weeks) were retrospectively examined. Prior to entry and upon completion of the program each individual completed a 6 minute walk test (6MWT), the SF-36 Health survey, and the UCSD Shortness of Breath Questionnaire (SOB). SF-36 results were analyzed according to 8 subscales [Physical Functioning (PF), Role Physical (RF), Bodily Pain (BP), General Health (GH), Vitality (V), Social Functioning (SF), Role Emotional (RE), and Mental Health (MH)]. Results: PR resulted in significant improvements in 6MWTdistance (Pre = 845 ± 37 ft, Post = 1127 ± 32 ft, p < 0.001), PF (p < 0.001), RF (p = 0.001), Vitality (p = 0.002), SF (p < 0.001), RE (p = 0.037), MH (p < 0.001) and SOB (Pre = 53 ± 2, Post = 47 ± 2, p < 0.001). The change in 6MWT distance was not related to changes in PF (r = 0.17), RF (r = 0.03), GH (r = 0.03), Vitality (r = −0.001), SF (r = 0.01), RE (r = 0.06), MH (r = −0.04) or SOB (r = 0.12). The magnitude of improvement in 6MWT distance (68%) was much greater than that observed in PF (15%), RF (16%), GH (6%), VT (18%), SF (20%), RE (14%), MH (14%), or SOB (8%). Conclusions: PR has a positive impact on 6 minute walk distance and perceived quality of life in individuals with COPD; however, changes in 6 minute walk distance appear to have no relationship to changes in perceived quality of life.
The American Thoracic Society (ATS) recommends that evaluation of patient-centered outcomes following pulmonary rehabilitation should reflect: (1) control of symptoms, (2) the ability to perform daily activities, (3) exercise performance, and (4) quality of life.1 The American Association of Cardiovascular and Pulmonary Rehabilitation (AACVPR) has identified 4 outcome assessment domains that should be assessed when evaluating the effectiveness of pulmonary rehabilitation. These domains are Health (health status), Clinical (dyspnea, fatigue, exercise performance, depression, or anxiety), Behavioral (smoking cessation, bronchial hygiene, supplemental oxygen use, etc), and Service (patient satisfaction).2
Various strategies are used by pulmonary rehabilitation programs to evaluate patient outcomes. Typically, patients are required to complete questionnaires or interviews that describe health related quality of life (HRQOL) and perceived dyspnea during daily activities before and after completion of the program. Patients are also required to complete an assessment of exercise performance or tolerance at the same time points. There is strong evidence that all of these measures show improvement following completion of a pulmonary rehabilitation program by patients with COPD.3
The HRQOL in patients participating in pulmonary rehabilitation programs reflect the impact of their disease process, its comorbidity, and the side effects of treatments on the patient's sense of well-being and ability to complete daily activities.1 Health related quality of life questionnaires have the ability to assess multiple domains including perceived functional status and overall satisfaction or dissatisfaction with life.2 The HRQOL questionnaires can be designed to assess general health (eg, SF-36) or directed to a specific disease process (eg, St. George's Respiratory Questionnaire or Chronic Respiratory Disease Question-naire).2 Numerous randomized control trials have demonstrated improvements in HRQOL in patients with COPD following pulmonary rehabilitation.3
Dyspnea is a central symptom of all patients with COPD who are referred to pulmonary rehabilitation.4 Dyspnea is a complex sensation that is theorized to arise from numerous mechanisms such as inadequate delivery of oxygen to working muscle, increased respiratory drive, inadequate gas exchange in the lung, and altered pulmonary mechanics.5 There are numerous tools that are used to evaluate dyspnea during daily activities in patients with COPD, including but not limited to: UCSD Shortness of Breath (SOB) Questionnaire,6 the Baseline Dyspnea Index,7 and the Modified Medical Research Council Questionnaire.8 Dyspnea during daily activities has consistently been shown to decrease following pulmonary rehabilitation. For example, in a study examining the effects of 12 weeks of pulmonary rehabilitation in 522 patients, responses to the UCSD-SOB questionnaire decreased an average of 6.8 units (nearly 12%) following completion of the program.6
The 6-minute walk test (6MWT) is one the most popular measures to evaluate changes in exercise performance subsequent to completion of a pulmonary rehabilitation program.9 Strict guidelines for completion of this test are provided by the ATS.9 The distance walked during the 6 MWT has also consistently been shown to improve in patients with COPD following completion of pulmonary rehabilitation. In a study completed by Mador and colleagues,10 distance walked during the 6MWT increased 86 feet (just under 7%) following completion of 8 weeks (24 sessions) of pulmonary rehabilitation. Similarly, Berry & associates11 described distance walked during the 6MWT to increase 200 feet (approximately 13%) following 12 weeks (36 sessions) of pulmonary rehabilitation.
Beyond the categorizations of outcome measures provided by the ATS and AACVPR, it is also possible to separate outcome measures into measurable functional outcomes (6MWT) and perceived outcomes (HRQOL and dyspnea during daily activities). Several investigators have completed cross-sectional investigations which have found HRQOL in patients with lung disease to be correlated to the distance walked during the 6MWT.6,12–17 For example, Chang and colleagues13 found that the physical component of the SF-36 (r = −0.51; p < 0.01) and disease specific HQROL (as measured by the St. George's Respiratory Questionnaire) (r = −.66; p < 0.01) to be negatively correlated to distance walked during the 6MWT in patients with interstitial lung disease. Similarly, Eakin and associates6 found disease specific HRQOL (as measured by the USCDSOB questionnaire) (r = −0.68; p < 0.001) to be negatively correlated to distance walked during the 6MWT in patients with various types of lung disease.
Establishment of a relationship between HRQOL measures and various clinical functional measures such as distance walked during the 6MWT is frequently used as an argument for inclusion of measurement of HRQOL in clinical assessment of patients.6,12,13 As a consequence, it seems logical that changes in measurable functional outcomes and perceived HRQOL outcomes subsequent to participation in pulmonary rehabilitation would be similar in direction and magnitude. However, little work has been done to determine if and how these changes in measurable functional and perceived HRQOL outcomes are related. A greater understanding of the relationships that exist between functional and perceived outcomes could impact clinical interpretation of data and be used in developing appropriate treatment approaches.
The purpose of this investigation was to examine the relationship between improvements in 6 minute walk distance and perceived quality of life in individuals with COPD following completion of a pulmonary rehabilitation program. It was hypothesized that changes in a measurable functional outcome (6MWT) would be positively correlated with changes in perceived outcomes (HRQOL) and dyspnea during daily activities.
The charts of all individuals enrolled in Alamance Regional Medical Center's (ARMC) LungWorks Pulmonary Rehabilitation program from January 2000 to June 2006 were reviewed for inclusion in this investigation. For inclusion into the study, patients had to: (1) have a diagnosis of COPD or other lung disorder, (2) have a physician referral for pulmonary rehabilitation, (3) be receiving optimal medical management for their condition as determined by the referring physician, (4) have a Forced Expiratory Volume (FEV1) or Forced Vital Capacity (FVC) of less than 70% of normal values, and (5) currently be a nonsmoker. One hundred sixty-six subjects were enrolled in the program during the allotted time frame. Of these, 139 (76 female, 63 male) completed the pulmonary rehabilitation program (Completers). In comparison, 27 patients did not complete the pulmonary rehabilitation program during this time frame. Unfortunately, complete patient records are only available for 20 (12 female, 8 male) of these 27 individuals. As a result, the data from these 20 individuals is used to represent the patients who did not complete the program (non-Completers). Explanations as to why these patients did not complete the program are not readily available; however, the clinical experience of the authors would suggest that most patients prematurely discharge themselves from the program for a variety of reasons including but not limited to: financial stress, access to transportation, perception of inability to meet the physical demands of the program, newly arisen medical issues, and personal responsibilities. As a result of not completing the pulmonary rehabilitation program, data is only available from their initial evaluation.
Prior to entry into the program all participants were subjected to a general physical therapy evaluation which included assessment of aerobic capacity (6 minute walk test; 6MWT), muscle strength (manual muscle testing), and joint range of motion. When appropriate, participants were evaluated for other disease specific issues such as balance, sensation, and gait mechanics. At this time, a respiratory therapist also evaluated the participant for static lung function and educational needs. After these initial evaluations, an appropriate individual treatment plan was developed that included aerobic conditioning, generalized muscle strengthening, stretching, patient education, and bronchial hygiene (when appropriate).
Participants then entered the pulmonary rehabilitation program and their individual treatment plan was applied for 24 sessions typically over an 8 week period. In general, the exercise stimulus included 45 minutes of aerobic exercise training and 15 minutes of generalized muscle strengthening. The aerobic exercise training included various modalities including treadmill walking, recumbent stepping, recumbent cycling, upright cycling, and upper extremity ergometry. During all aerobic exercise, exercise intensity was altered so that subjects maintained a rating of perceived exertion (RPE) ranging from 12 to 14 on the 20 point Borg RPE scale,18 a perceived dyspnea ranging from 3 to 5 on the 10 point Borg Breathlessness Scale,18 and oxygen saturation above 90%.
All data for this study was obtained by retrospective chart review. The protocol for obtainment of the data was reviewed and approved by the Institutional Review Board of Alamance Regional Medical Center. Data was provided to the primary investigator by an appropriate institutional representative in a de-indentified state. All patient information was handled according to the guidelines of the Health Insurance Portability and Accountability Act (HIPAA). Descriptive data recorded from the patient's chart included age, gender, weight, height, FEV1, and FVC. Also collected from the patient's chart were their responses to several outcomes measures immediately before entry and upon completion of the pulmonary rehabilitation program. These measures included 6 minute walk distance, responses to the Short Form 36 (SF-36) Health Survey, and the UCSD Shortness of Breath Questionnaire. Data from subjects who did (139) and did not (20) complete the pulmonary rehabilitation program were included in this investigation in an effort to determine if the relationships between improvements in 6 minute walk distance and perceived quality of life were influenced by pretreatment measures.
This test was performed in a carpeted hallway using a marked 100 foot walkway. The procedures used by the American Thoracic Society for the 6MWT were applied in all instances.9 Each patient was given the same instructions as to the procedures of the test, and was required to walk independently. The distance a patient walked in 6 minutes was recorded to the nearest foot. The reliability and validity of the 6 MWT has been previously summarized in the literature.19 The minimal clinically important difference (MCID) for the 6MWT has conservatively been estimated to be 54 to 80 meters (177 to 262 feet).20
This questionnaire uses 36 questions to allow the patient to rate his or her health in a general sense.21 It can be used for patients with all diagnoses, not just COPD. The answers were scored and 8 different subscale ratings were produced: Physical Functioning, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional, and Mental Health.21 A consensus on MCIDs for the 8 subscales of the SF-36 are not readily available. Working with an expert panel of physicians, Wyrwich and colleagues22 describe clinically important differences (CID) for the 8 subscales to range from 5 to 12.5 units (Physical Function=5, Role Physical=6.25, Bodily Pain=10, General Health=5, Vitality=6.25, Social Functioning=12.5, Role Emotional=8.33, Mental Health=5).
This 24 item measure is specific to pulmonary disease and assesses self-reported shortness of breath while performing various ADLs.6 The UCSD-SOB is a valid tool for clinical and research applications of COPD patients.6 The MCID for the UCSD-SOB has been determined to be 5 units.23
Differences between patients who did (Completers) and did not complete (non-Completers) the program and changes in outcomes measures as a result of pulmonary rehabilitation were evaluated using an incomplete Multiple Analysis of Variance (MANOVA).24 Comparisons between Completers and non-Completers were made in an effort to determine if preexisting differences in patients may have influenced the relationships between functional and perceived outcomes. Relationships between relative changes in 6MWT distances, SF-36 scores, and UCSD-SOB scores were evaluated using correlation (Pearson Product Moment) analysis. Significance level for all analyses was set apriori at p ≤ 0.05.
Demographic data of subjects is presented in Table Table1.1. No differences existed in demographic data (age, height, weight, BMI, FVC, and FEV1) between patients who did and did not complete the pulmonary rehabilitation program. Upon entry, patients who completed the program covered a greater distance (845 ± 37 feet) during the 6MWT and compared to the patients who did not complete the program (567 + 77 feet) (p = 0.002). There was no difference at the beginning of the program in the UCSD-SOB questionnaire score between those who did (53 ± 2) and did not (62 ± 5) complete the program (p = 0.08). Of the 8 subscales of the SF-36; Physical Function (completers=25.1 + 1.4; non-completers=12.5 + 2.7) (p = 0.01), General Health (completers=41.3 + 1.5; non-completers=68.5 + 2.3) (p < 0.001), and Vitality (completers=47.6 + 2.6; non-completers=67.4 + 4.6) (p = 0.005) were different at the beginning of the program between those who did and did not complete the program.
Following participation in pulmonary rehabilitation, distance covered during the 6MWT increased from pre (845 + 37 feet) to post (1127 + 32 feet) (p < 0.001) (Figure (Figure1).1). This change is equivalent to a 68 + 12% increase in the distance covered during the 6MWT (Figure (Figure4).4). In comparison, the UCSD-SOB questionnaire score decreased from pre (53 + 2) to post (46 + 2) (p < 0.001) (Figure (Figure2).2). This change is equivalent to a 7.5 + 3.0% decrease in perceived breathlessness (Figure (Figure44).
Of the 8 subscales of the SF-36, Physical Function (pre=25.1 + 1.4; post = 34.9 + 1.7) (p < 0.001), Role Physical (pre=23.3 + 2.8; post=38.5 + 3.1) (p = 0.001), Vitality (pre=47.6 + 2.6; post =56.6 + 2.2) (p = 0.002), Social Function (pre = 7.0 + 0.2; post = 7.9 + 0.2) (p < 0.001), Role Emotional (pre = 28.3 + 2.2; post = 34.6 + 2.3) (p = 0.037), and Mental Health (pre = 73.3 + 1.5; post = 83.2 + 1.3) (p < 0.001) improved following participation in pulmonary rehabilitation (Figure (Figure3).3). The only subscales that did not improve following participation were General Health (pre = 41.3 + 1.5; post = 44.0 + 1.7) (p = 0.226) and Bodily Pain (pre = 63.1 + 1.9; post = 70.1 + 5.3) (p = 0.212). The relative changes in each subscale are presented in Figure Figure44.
The correlations between the change in distance covered during the 6MWT and each of the perceived outcome measures were poor (Table (Table2).2). The only significant correlation found was between the 6MWT and the Physical Function (p=0.04) subscale of the SF-36; however, the r value (r = 0.17) suggests that this relationship is not practically important. Poor relationships were also observed between the change in distance covered during the 6MWT and the PCS (r=0.11, p=0.68) and MCS (r=0.004, p=0.96) produced by the SF-36.
The findings of this investigation indicate that participation in a pulmonary rehabilitation program results in significant improvements in both physical function, as measured by distance covered in 6MWT (Figure (Figure1),1), and measures of quality of life [UCSD-SOB (Figure (Figure2),2), and SF-36 (Figure (Figure3)].3)]. In this investigation, scores for 6 of the 8 subcategories of the SF-36 improved, with significant increases observed for Physical Function, Role Physical, Vitality, Social Function, Role Emotional, and Mental Health. The only subscales that did not show an improvement were General Health and Bodily Pain. These results are similar to those reported by Ferrari and associates,25 who showed improvements in physical function and on 6 of the 8 SF-36 subscales. In the investigation by Ferrari and associates,25 Bodily Pain and Social Function failed to show improvements following pulmonary rehabilitation. In comparison, Boueri and colleagues26 reported improvements in only 4 of the 8 SF-36 subscales following pulmonary rehabilitation, with no changes in Bodily Pain, Role Physical, Social Function, or General Health.
Across these investigations, the consistent finding that Bodily Pain does not change following pulmonary rehabilitation seems appropriate since pain is not typically a primary complaint of patients with COPD and pulmonary rehabilitation programs do not directly address pain in their treatment paradigm. This investigation may have resulted in changes in Role Physical and Social Function while Boueri et al26 did not, simply because of a larger sample size. The sample size in this investigation (n = 139) is nearly 4 times greater than that used in the investigation by Boureri and colleagues.26 In their investigation, both Role Physical (p = 0.32) and Social Function (p = 0.06) tended to improve following pulmonary rehabilitation; however, the error within these measures was too great to see a statistical difference. It seems likely that a larger sample size may have produced a smaller error and revealed statistical differences in these 2 measures. In comparison, Ferrari and associates25 observed essentially no change in Social Function and it is very unlikely that sample size influenced this finding. Similarly, Boureri and colleagues26 observed no change in General Health, while this investigation and that of Ferrari and associates25 found significant improvements in this measure. Potential explanations for these seemingly contradictory findings are not obvious when reviewing the methodology of these investigations. What does seem obvious is that more consistent reporting of these measures is needed in the literature in order to fully understand this phenomenon.
Perceived shortness of breath during functional activities, as measured by the UCSD-SOB questionnaire, also improved following pulmonary rehabilitation in this investigation. In fact, a 12% reduction in SOB was observed following completion of the program. These results are greater than the MCID22 previously reported for the UCSDSOB and are similar to those described by the California Pulmonary Rehabilitation Collaborative Group (CPRCG),16 who reported an approximate 12% reduction in SOB. Reductions in perceived dyspnea are a consistent benefit to patients with COPD who participate in a pulmonary rehabilitation program. While the sample-size (415 patients) used in the investigation by the CPRCG is significantly greater than that using in this investigation, comparison of the findings of these two investigations seems appropriate since the subjects have similar demographic information (age, gender, FEV1), the information was collected in a similar context (pulmonary rehabilitation), and much of the same information (6MWT, UCSD-SOB, SF-36) was examined.
We also observed a significant improvement in distance covered during the 6MWT. The improvement observed in this investigation (68 ± 12%) in 6MWT distance is quite dramatic compared to the changes reported by other investigators. For example, Berry and associates11 reported an approximate 13% improvement in 6MWT distance. This observation is potentially explained by the shorter distance covered in pretesting by our participants (845 ± 37 ft), as compared to that in other studies (Berry, et al;11[1485 ± 87 ft]) (California Pulmonary Rehab Collaborative Group;16 [1032 ± 18 ft]), suggesting that the participants included in this investigation entered the pulmonary rehabilitation program at a lower functional capacity than the participants in these other studies. Since the 6MWT is a test limited to “walking” it appears that the greatest distance obtainable is approximately 600 m (1968 feet).28,29 As a consequence, the potential room for improvement in this variable is greater in patients who enter a program with lower initial 6MWT distances. Interestingly, the % predicted FEV1 of the participants in this study (44.7 ± 1.7%) is nearly identical to that reported by the California Pulmonary Rehab Collaborative Group16 (44.4 ± 0.84%).
As mentioned previously, the MCID for the 6MWT has been estimated to range between 54 to 80 meters (177 to 262 feet).20 The 282 foot average increase in distance walked during the 6MWT in this investigation indicates that the intervention (pulmonary rehabilitation) was successful at improving this outcome from a clinical perspective. The ATS states that a practice 6MWT is not needed in most clinical settings, but it should be considered.9 Sciurba and colleagues27 found the distance walked during the 6MWT to increase 7% (66 ft) from the first to second trials in 437 patients with severe emphysema. It is also unclear if the performance of a initial 6MWT impacts the performance of a postintervention test completed at later time point (8 weeks or more) or if a familiarization test is needed at the end of a training program.28 Hill and colleagues30 found a 9 m (29 ft) increase in 6MWT distance as a result of a familiarization test following completion of an 8-week training program. As a consequence, it is possible that some of the improvement in the distance walked during the 6MWT seen in this investigation following completion of the pulmonary rehabilitation program is a result of a practice effect. It is also possible that this phenomenon could influence the relationships between outcome measures discussed below. It seems prudent that future investigations which include 6MWT distance as a dependent variable, should closely consider the need for inclusion of familiarization tests in their experimental design.
The primary purpose of this investigation was to examine the relationship between changes in 6MWT distance following completion of pulmonary rehabilitation and perceived quality of life in patients with COPD. While all of these measures showed consistent improvement following pulmonary rehabilitation, changes in 6MWT distance were clearly not related to changes in perceived quality of life (Table (Table2).2). This lack of relationship between functional outcomes and perceived outcomes is similar to that seen by other investigators26,31 and may have potential implications to clinical practice.
As described previously, numerous investigators have reported significant correlations between HRQOL and distance walked during the 6MWT at a specific point in time.12–17 In contrast, the few investigations that have attempted to describe a positive relationship between improvements in distance walked during the 6MWT and HRQOL have consistently been unsuccessful. For example, Boureri and associates26 found poor relationships (r no greater than 0.16) between the improvements in distance walked during the 6MWT and each of the subscales of the SF-36 in patients with COPD after completion of a 3week pulmonary rehabilitation program. Similar findings are described by de Torres and colleagues31 who investigated these relationships subsequent to 6 to 8 weeks of pulmonary rehabilitation in patients with severe COPD (FEV1 < 40%). While these authors report that changes in distance walked during the 6MWT did not correlate with changes in any of the HRQOL tools used (such as the SF36, Chronic Respiratory Disease Questionnaire and the St. George's Respiratory Questionnaire), improvements in the various HRQOL tools were consistently correlated with each other.31
When discussing the lack of relationships between improvements in HRQOL and increases in the distance walked during the 6MWT, authors typically conclude that the 6MWT and measures of HRQOL are measuring different constructs.25,26,31 At one level this seems like a reasonable conclusion since the 6MWT is a measure of physical capacity, while measures of HRQOL evaluate perceptions of physical capacity. Another possible explanation for this lack of relationship is that the 6MWT does not reflect the same scope of function as measures of HRQOL. More specifically, we are suggesting that the functional activities associated with performance of the 6MWT are not always the same as the functional activities addressed in the measures of HRQOL used in this and other investigations.
Component analyses of these measures seem to support this idea. The 6MWT requires subjects to walk on an even level surface for 6 continuous minutes. Donelan and colleagues32 describe the energetic cost of walking to be primarily (92%) related to lower extremity activity (supporting body weight=28%, generating propulsion=48%, swing the legs=10%, and stabilizing laterally=6%). In contrast, the SF-36 and UCSD-SOB questionnaires seem to reflect a broader range of physical activities. For example, the SF-36 asks patients to evaluate tasks like walking up and down stairs and carrying groceries. Similarly, the UCSD-SOB questionnaire asks patients to address their ability to bathe themselves, vacuum, and complete various other activities. While the ability to walk on level ground certainly would influence a patient's ability to complete these tasks, it seems obvious that the 6MWT does not represent all of the physical demands of activities of daily living such as carrying groceries, bathing, or vacuuming.
One of the glaring functional areas missing from the 6MWT is significant use of the upper extremities. Interestingly, the use of a continuous upper extremity assessment of function seems to be nearly absent from the pulmonary rehabilitation literature. Furthermore, there is no mention of such an assessment in the Guidelines for Pulmonary Rehabilitation Programs, 3rd edition provided by AACVPR.2 In 2 of the few investigations using such a task, Berry and colleagues11,33 asked participants to raise their arms so that they were parallel to the ground and then move three 2.5 lb weights across a row of 4 pegs as quickly as possible. Significant improvements in time to complete this task were seen following completion of a traditional pulmonary rehabilitation program over 12 weeks.11 The magnitude of change in this upper extremity task (about 5%) seems to be more consistent with the magnitude of change seen in measures of perceived quality of life than those seen in the 6MWT. Consequently, further development and implementation of an assessment tool that evaluates continuous function of the upper extremities in patients with COPD participating in pulmonary rehabilitation seems appropriate.
Another important area of discussion related to the findings of this investigation is associated with the exercise stimulus or prescription used in most pulmonary rehabilitation programs. While virtually all pulmonary rehabilitation programs include exercises that are aerobic and resistive in nature and require use of both lower and upper extremities, honest review of most programs would likely conclude that a disproportionate amount of time and effort is dedicated to aerobic activity that predominately requires use of the lower extremities. The lack of association in the functional outcome (6MWT distance) and perceived quality of life found in this and other investigations could suggest that this strategy may not be optimal to improve perceived quality of life in patients with COPD. A recent update of the guidelines jointly provided by the American College of Chest Physicians (ACCP) and AACVPR2 strengthens the recommendations for inclusion of strength training and unsupported endurance training of the upper extremities in pulmonary rehabilitation; however, the impact of these strategies on perceived quality of life remains unclear.
A potential limitation of this investigation, is related to the specific HRQOL tools used (ie, SF-36 and UCSD-SOB). There are numerous HRQOL outcome measures that have been effectively used in this population and it is possible that more positive findings could have existed if different tools were used. This possibility seems unlikely since previous investigators have reported similar findings using a variety of HRQOL measures.25,26,31
Interestingly, differences were seen at the beginning of the pulmonary rehabilitation program in distance walked during the 6MWT, the UCSD-SOB, and several subscales of the SF-36 (Physical Function, General Health, and Vitality) between participants who did and did not complete the program. These findings are contradictory to each other and difficult to interpret. While patients who did not complete the program had lower distances during the 6MWT, greater shortness of breath during daily activities, and a worse perception of their physical function upon entry into the program, they also had more positive perceptions of their general health and vitality. Little work has been done to investigate the issues of non-adherence to a pulmonary rehabilitation program in patients with lung disease. The few investigations that have explored the issue suggest that non-adherence is more likely to be associated with social issues such as marital status and convenience and not associated with any physiologic or perceptual measures.34,35 The relevance of these specific findings to the general findings of this investigation are not clear to the authors; however, since there were differences between completers and noncompleters of the program in many of the variables central to the investigation it is prudent to consider this issue in any future investigation of this phenomenon.
In summary, improvements in functional and perceived outcomes were seen following pulmonary rehabilitation; however, changes in functional measures were not correlated to changes in perceived function. Furthermore, the magnitude of improvement in the functional measure was much greater than seen in the perceived measures. These findings could have implications to clinical practice and suggest that the 6MWT alone may not be the most optimal means to evaluate improvements in physical function in patients with COPD following pulmonary rehabilitation.