Six-minute walk performance and quality of life comparisons in North Carolina cardiac rehabilitation programs☆☆☆

Article Outline

• Abstract
• Methods
  • Subjects
  • CR programs
  • Administration of the 6-minute walk tests
  • Administration of the Ferrans and Powers QOLI
  • Clinical database and statistical analysis
• Results
  • Six-minute walk
  • Ferrans and Powers QOLI
• Discussion
  • Six-minute walk performance
  • Effect size
  • QOLI
• Limitations
• Clinical implications
• Conclusions
• Acknowledgements
• References
• Copyright

Abstract 

Objective: The purposes of this study were (1) to determine if six-minute walk (6MW) performance improved after short-term cardiac rehabilitation (CR) across multiple outpatient programs; (2) to examine differences in 6MW performance by patient age, sex, and race; and (3) to determine what relationships existed, if any, between 6MW performance and subscales of the Ferrans and Powers' Quality of Life Index—Cardiac Version III (QOLI). Design: Study design was nonexperimental, prospective, and comparative. Setting: Study setting included 14 outpatient CR programs from urban and rural settings across North Carolina. Patients: Adults aged 40 to 89 years (N = 630; men = 424 [67%], women = 206 [33%]; mean age, 61 ± 10.32 years) with medically or surgically treated coronary heart disease enrolled in outpatient CR. Outcome Measures: Study measures included scores on the QOLI and distance walked (feet) on the 6MW test. Results: Six-minute walk tests and QOLI surveys were administered before and immediately after short-term CR participation. Six-minute walk distance increased for all patients in all age categories across programs after CR (P <.0001). As a group, women improved 6MW distance by 15% (1243.9 ± 301.2 to 1435.3 ± 298.1; P <.001). Men also improved 6MW distance by 15% (1463.3 ± 339.5 to 1683.7 ± 346.9; P <.001) and walked farther than women on both the initial and follow-up 6MW tests (P <.0001). By age, there were no differences in 6MW scores between men and women aged 40 to 49 years (n = 58) and 50 to 59 years (n = 140; P = 0.54). Both of these age groups had greater initial and discharge 6MW scores than those aged 70 to 79 years (n = 183) and 80 to 89 years (n = 22; P <.001). Those aged 60 to 69 years (n = 227) had lower 6MW scores than those aged 40 to 49 years (P = 0.001) and 50 to 59 years (P <.05), and greater scores than those aged 70 to 79 years (P <.05) and 80 to 89 years (P <.05). Those aged 70 to 79 years had greater initial and follow-up 6MW scores than those aged 80 to 89 years(P <.001). Overall improvements in 6MW performance were found in both white subjects (n = 575; P <.001) and African-Americans (n = 54; P <.001). There were no apparent relationships between 6MW performance and overall or Health and Function QOLI scores (r <.21). Conclusions: Participation in short-term outpatient CR improved 6MW performance in patients aged 40 to 89 years across 14 programs in North Carolina. No relationships were found between 6MW performance and any domain of the QOLI, including the Health and Function domain. (Heart Lung® 2003;32:41-51.)

To accurately assess improvements in specific health categories in patients of outpatient cardiac rehabilitation (CR) programs, a systematic measurement of treatment outcomes is required. The American Association of Cardiovascular and Pulmonary Rehabilitation (AACVPR)¹ and others², ³, ⁴, ⁵, ⁶, ⁷ have indicated that CR outcomes should include ongoing measures of physical performance, behavioral or psychologic domains, nutritional parameters, quality of life, recurrent cardiac events, social interactions, and self-efficacy. Although it has been well-established that CR improves both physical work capacity and quality of life in cardiac patients,¹, ², ⁸, ⁹, ¹⁰ little is known about how these two parameters interrelate. Moreover, although physical work capacity and quality of life are important as measurable outcomes for justifying CR intervention, there is not a consensus on the best methodology to assess these measures across programs for both sexes. Clinical outcomes have only recently been examined after CR intervention from multiple sites, providing “real-life” evidence of the benefits of multidisciplinary CR for health care organizations and insurance companies.⁸, ⁹, ¹⁰

In recent years, timed walking tests such as the 6-minute walk (6MW) have gained prominence for use in clinical practice and research settings to assess changes in functional capacity after CR intervention. The 6MW test is a convenient, safe, inexpensive, noninvasive test used routinely in primary and secondary disease intervention programs as one indicator of fitness. This test has been shown to be both valid and reliable in cardiac populations.¹¹, ¹², ¹³, ¹⁴, ¹⁵ The 6MW test may be more reliable for serial comparisons in multiple CR programs than standard treadmill exercise tests. However, both types of tests have limitations because protocols often vary by facility, test supervisor, test end-points, parameters measured, and test location (eg, oval track vs hallway for 6MW) (Table I).¹⁴, ¹⁵, ¹⁶, ¹⁷

Table I. Strengths and weaknesses of timed walking tests in cardiopulmonary rehabilitation^*

GXT, Graded exercise test; VO_2peak, peak oxygen consumption during a graded exercise test; METS, metabolic equivalents.

Although 6MW test norms are available for healthy populations,¹⁸, ¹⁹ to our knowledge these have not been published for men and women with chronic cardiopulmonary disease. Interrelationships found between 6MW performance and other measures of physical impairment, such as self-efficacy and performance of daily living activities, have been mixed in patients with chronic cardiopulmonary disease.¹¹, ²⁰, ²¹

In 1997, the North Carolina Cardiopulmonary Rehabilitation Association (NCCRA) began to assess clinical outcome measures in patients from programs statewide after CR participation with the 6MW (and other) tests. Psychosocial and behavioral characteristics were measured with the Ferrans and Powers Quality of Life Index—Cardiac Version III (QOLI).¹⁰, ²², ²³, ²⁴ All state-certified programs were invited to participate in this ongoing study. Thus, the purposes of this investigation were (1) to determine if, and to what extent, 6MW performance improved after short-term multidisciplinary CR across multiple outpatient programs; (2) to determine what differences existed in 6MW performance by patient age, sex, and race; (3) to determine what relationships existed, if any, between specific domains of the QOLI and 6MW performance; and (4) to develop a database for benchmarking 6MW and QOLI data with other affiliate CR societies for the establishment of normative values for cardiac patients.

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Methods 

Subjects 

The subjects for this investigation consisted of 424 men and 206 women aged 40 to 89 years from 14 North Carolina early outpatient (Phase II) CR programs. Patients were tested between January 1, 1997, and December 31, 2000. Only those patients who completed both the initial and follow-up test procedures were included in this study. Patient age, diagnosis, and ethnicity were typical for North Carolina CR programs (Table II).

Table II. Descriptive characteristics of the sample (N = 630)

CAD, Coronary artery disease.

The medications taken by participants were not tracked, but they were typical for patients with cardiovascular disease who participate in rehabilitation programs. The vast majority of patients were white, with less than 10% African-American and less than 1% either Asian-American or Hispanic. Although these data vary from the overall demographic distribution of people in North Carolina, they are consistent with the patient distribution of minorities in North Carolina CR programs, who are generally underrepresented.

CR programs 

In North Carolina, each CR program undergoes a state governed certification process under State Statute 131-E, Article 8. All programs that participated in this investigation were certified by the Division of Facility Services of the state of North Carolina and staffed in accordance with the Certification Procedures for Outpatient Cardiac Rehabilitation Programs in North Carolina.²⁵ These rules are in agreement with guidelines and recommendations established by the AACVPR,² the American College of Sports Medicine,³, ²⁶ and the American Heart Association.²⁷, ²⁸ All programs provided exercise therapy consistent with the guidelines in the Certification Procedures.²⁵ The mode of exercise therapy included walking, jogging, aquatic activity, cycle ergometry, arm ergometry, stair climbing, rowing, aerobics, step aerobics, and resistive training. The duration of exercise was up to 60 minutes each session (as tolerated) including a minimum of 5 minutes each for warm-up and cool-down exercises. Exercise sessions were performed a minimum of 3 days per week. The intensity of exercise was determined from one (or more) of the following techniques: (1) up to 85% of symptom-limited heart rate reserve, (2) up to 80% of measured maximal oxygen consumption, (3) a rating of perceived exertion from 11 to 13 on the Borg category scale², ³, ²⁶ if an entry graded exercise test was not available, or (4) an exercise heart rate not to exceed 20 beats per minute above standing resting level without a graded exercise test in patients with previous myocardial infarction or 30 beats per minute above standing level in patients who had coronary artery bypass graft surgery. All patients were monitored during rehabilitation sessions with either continuous telemetry or intermittent “quick check” defibrillator checks. The frequency of electrocardiographic monitoring was determined by medical acuity and risk stratification. The patient's rate of exercise progression was assessed every 2 weeks. The exercise prescription was modified by the program's exercise specialist on the basis of the patient's past performance, medication changes, exercise test results, physician instructions, and overall cardiovascular status.

Each program also offered nutritional, vocational, and psychosocial assessment and counseling. Behavioral counseling, if indicated, was provided by a mental health professional who met state guidelines for this type of intervention. Education was offered throughout programs covering risk factor modification, dietary modification, stress management, lipid management, weight loss, smoking cessation, musculoskeletal injury prevention, and overall cardiovascular disease intervention. Rehabilitation staff included the medical director, program director, certified exercise specialists, registered nurses, registered dietitians, psychologists, clinical social workers, occupational therapists, physical therapists, and vocational rehabilitation counselors.

Administration of the 6-minute walk tests 

All initial 6MW tests were performed within the first week of admission to the outpatient program. Follow-up testing was performed within 10 to 12 weeks at Phase II discharge or entry into a Phase III or cardiac maintenance program. Standardized instructions for administration of each test were sent to all CR program directors. Patients were instructed to walk as far as possible in a 6-minute time period, taking rest periods if necessary. The time elapsed and statements of encouragement were provided at standardized intervals during tests in accordance with established testing procedures.¹¹, ¹⁴, ¹⁵ Those with musculoskeletal problems that limited walking and those with cardiovascular contraindications (eg, uncontrolled angina, hypertension, or dysrhythmias) were excluded from testing. The total distance walked was measured to the nearest foot and recorded. Before each test, the patient's resting heart rate and blood pressure were monitored in a resting, sitting position. Immediately after completion of the 6MW test, a CR staff member measured peak exercise data including heart rate, blood pressure, rating of perceived exertion, and total distance walked. Other measured parameters included number of rest periods, duration of rest periods, angina ratings, dyspnea ratings, and pulse oximetry recordings. These measures, which varied by the program, were taken primarily for patient monitoring and safety purposes and were not formally collected or analyzed. Patients who became symptomatic (eg, angina, severe dyspnea) were instructed to stop walking and the test was discontinued. There were no reported cardiopulmonary complications requiring physician intervention during testing throughout programs.

Administration of the Ferrans and Powers QOLI 

The QOLI is a self-administered, 72-item life satisfaction scale that asks respondents to rate their level of satisfaction and importance of a particular area in their life. The 4 domains measured are health and function, socioeconomic status, psychologic or spiritual status, and family interaction. An overall score indicates cumulative summary scores of all domains. Ratio scores are calculated to yield weighted scores on a 0 to 30 scale, with 30 as the highest score attainable in a specific domain. Previous studies have reported an average standard deviation of 4.5 points for each domain of the QOLI, with an increase or decrease of 2 points indicating a clinically meaningful difference.²⁴ The internal consistency reliability for each of the 4 QOLI subscales has been shown to be favorable (0.86-0.98) in cardiac patients²⁹, ³⁰, ³¹, ³², ³³ and other illness groups.³⁴, ³⁵, ³⁶, ³⁷, ³⁸ This tool has also been shown to have good content and construct validity.²², ²³, ²⁴, ³⁰, ³⁵ In previous investigations, CR patients have exhibited higher QOLI scores than other illness groups¹⁰, ³⁹ and similar scores to the general population.²⁹

As with the 6MW tests, the QOLI was administered to all patients within the first week of CR admission and again upon completion of the program. A standardized set of instructions for test administration was sent to all program directors. Patients were instructed to complete the survey themselves, without help from spouses or other family members, in a private area. The average survey administration time was 10 to 15 minutes. Once completed, QOLI scores were entered by a CR staff member into a Windows software program to provide summary scores for each of the 4 subscales and the overall score. Program staff then sent all scores to the coordinating center for data entry and analysis. Although some programs chose to incorporate this survey as their permanent assessment tool, others offered the QOLI in addition to the tool that they were currently using.

Clinical database and statistical analysis 

A multi-site database was established in voluntary cooperation with participating NCCRA program directors. This database contained information from participants enrolled in 14 hospital-based and free-standing outpatient CR programs between January 1, 1997, and December 31, 2000. The Northeast Medical Center Clinical Research Institute in Concord, North Carolina, served as the coordinating center with the support of the Davidson College Psychology Department in Davidson, North Carolina. Once data entry forms were received from each program, 6MW distance (feet) and QOLI scores in each domain (0-30 scale) were entered into an SPSS for Windows Version 10.0 (SPSS, Inc; Chicago, IL) software program for statistical analysis. For participating in this investigation, each program director received a summary report that included personalized data for their program compared with state and population norms for the 6MW and QOLI scores.

Initial and follow-up 6MW distances were analyzed for differences by sex, age, and race with a repeated measures analysis of variance. Changes were considered statistically meaningful at the .05 level of significance. Tukey post-hoc analysis was used to detect specific differences between age groups for the 6MW scores. Clinically meaningful changes for 6MW scores have not been established in cardiac patients. Thus, the effect size, which represents a standard measure of change, was calculated as the difference between the initial and follow-up 6MW score means divided by the initial 6MW score standard deviation of the mean: (mean initial scores − mean follow-up scores)/SD of initial scores.²⁰ Initial and follow-up 6MW scores were also compared with the each subscale and the overall score of the QOLI with Pearson correlation coefficient analysis.

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Results 

Six-minute walk 

Six-minute walk distance increased for all patients in all age categories across programs after multidisciplinary CR (P <.0001) (Table III). Men walked farther than women on both the initial and follow-up 6MW tests (P <.0001). Although both sexes showed a statistically significant improvements in 6MW distance after CR, men showed a greater overall improvement in walking distance.

Table III. 6-Minute walk improvement in North Carolina cardiac rehabilitation patients^*

Tukey post-hoc analyses showed that there were statistical differences in 6MW performance between specific age groups when men and women were grouped together. Although there were no differences in 6MW scores between those aged 40 to 49 years (n = 58) and 50 to 59 years (n = 140; P = .54), both of these age groups had greater initial and discharge 6MW scores than those aged 70 to 79 years (n = 183) and 80 to 89 years (n = 22; P <.001). Those aged 60 to 69 years (n = 227) had lower 6MW scores than those aged 40 to 49 years (P = .001) and 50 to 59 years (P <.05), and greater scores than those aged 70 to 79 years (P <.05) and 80 to 89 (P <.05). Those aged 70 to 79 had greater initial and follow-up 6MW scores than those aged 80 to 89 years (P <.001).

Overall improvements in 6MW performance were found in both white subjects (n = 575; P <.001) and African-Americans (n = 54; P <.001). However, white men and women had significantly greater initial (1414.7 ± 340.7 ft) and follow-up (1632.1 ± 348.8 ft) 6MW scores compared with African-American patients (initial, 1233.0 ± 358.0 ft; follow-up, 1421.0 ± 340.7 ft). Asian and Hispanic patients (n = 2) were not included in these analyses.

Ferrans and Powers QOLI 

We previously reported significant improvements in most categories of the QOLI in both men and women after short-term CR participation.¹⁰ To determine if any relationships existed between QOLI scores and 6MW performance, the QOLI initial and follow-up scores in each domain (psychosocial/spiritual, health/function, socioeconomic, and family) and the overall score were correlated with a measure that compared the improvement between the initial and follow-up 6MW scores in all patients by age group. Although a small number of these correlations were statistically significant as a result of the large sample size, all correlation coefficients were low (r <.18). To additionally examine the health/function domain, a subscale of particular interest with regard to functional abilities, we looked for any relationships between these scores and the reported initial and follow-up 6MW scores. All correlation coefficients were again low, ranging from 0.12 to 0.19 for the initial and 0.20 to 0.24 for the discharge scores. Given the lack of practical significance of these correlations, no additional analyses were performed because it did not appear that any QOLI domain was systematically related to 6MW scores for any age group or patients as a whole.

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Discussion 

Timed walking tests have become increasingly popular for quantification of physical function and activity status for patients in CR programs. This popularity results from many factors, one being that CR staff are now more accepting of entering participants without having the results of a symptom-limited graded exercise test. Both timed walking tests and graded exercise tests have limitations because test validity is often hindered by (1) lack of metabolic analysis, (2) treadmill handrail holding by the patient that may overestimate the patient's functional capacity, (3) previous practice by the patient in preparation for the test, and (4) the inability to directly translate heart rate and perceived exertion parameters from the exercise test to the CR training environment.¹⁷ Although nuclear and magnetic resonance imaging studies can provide useful quantitative cardiac pathology information, they often lack adequate information for exercise prescription (eg, adenosine or persantine technetium sestimibi studies). As a result of these (and other) factors, the ability to establish the patient's functional capacity, exercise prescription, cardiac risk status, personal goals, and training regimen may be hindered.

It is now apparent that there is a need for alternatives to the graded exercise or nuclear stress test for exercise assessment needs in CR programs. Timed walking tests are less expensive than graded exercise or nuclear tests, easier to administer, require less use of staff and equipment, are performed during a shorter time period, and may pose less risk of cardiovascular complications for the patient, although additional research is needed on this issue. Although the 6MW test does not provide as much clinical information as either the graded exercise or nuclear stress study, this test still may help alleviate some of the aforementioned deficiencies and may decrease the need for follow-up graded exercise or nuclear imaging studies for the “long-term” or maintenance CR participant. The 6MW test is also quite practical for assessing gross functional improvements over time in low-fit CR participants and other chronically diseased populations for optimal tracking of patient outcomes.

This multiple site study was designed to evaluate functional status and health-related quality of life relationships in cardiac patients after short-term CR intervention. Although the participating CR programs may have differed in staff and structure, their assessment measures were standardized for uniform outcome data tracking. Analyzing data in this fashion from several outpatient facilities may offer a better look at the “real-life” benefits of CR and can contribute to the establishment of normative values.

Six-minute walk performance 

In this cohort of patients, 6MW performance improved from 11% to 20% after CR intervention (Table III). Women improved 6MW scores from 11% (50-59 age group) to 20% (80-89 age group) for an overall group increase of 15%. Similarly, men improved 6MW distance from 12% (80-89 age group) to 16% (50-59 and 70-79 age groups) for an overall group increase of 15%. Both men and women improved overall 6MW performance by 15%. These improvements are somewhat less than observations of Jungbauer and Fuller⁸ in 928 men and women from outpatient CR programs in Indiana. In their investigation, men and women were looked at as a group and 6MW distance increased from 1248 ± 380 ft to 1567 ± 583 ft for a 26% overall improvement after 12 weeks of supervised CR. The lower improvement observed in the present study may have been a result of the intensity of training employed at the various CR sites, the total number of sessions patients attended in a 10- to 12-week period, or demographic characteristics of the North Carolina patients compared with the Indiana patients. Because Jungbauer and Fuller⁸ reported the findings of men and women as a group, it may be that individual differences in rates of improvement existed between sexes but were not reported.

Our findings agree with those of Gibbons et al¹⁸ in apparently healthy patients and Hamilton and Haennel¹¹ in CR participants. Both studies found 6MW performance to be inversely related to age and to be greater in men than in women. Although no direct relationship between age and 6MW distance was seen in the present study, 6MW performance tended to decline with age in most age groups. As a group, men walked farther than women on both the initial (men, 1463.3 ± 339.5 ft; women, 1243.9 ± 301.2 ft) and follow-up (men, 1683.7 ± 346.9 ft; women, 1435.3 ± 298.1 ft) 6MW tests (P <.001). This was interesting, considering that older men and women are often comparable in their degree of functional impairment and thus should hypothetically perform similarly. This difference may have resulted from men's longer stride during 6MW testing,¹⁹ a greater aerobic capacity, or both.

Both white and African-American patients improved 6MW performance after short-term CR intervention. White subjects as a group performed better than African-Americans on both the initial and follow-up 6MW tests, although this result is preliminary as a result of the low statistical power of the African-American patients sampled (n = 54). This finding amplifies the need for better efforts to enlist and retain African-American patients in CR programs. Only then can we devise a solid advocacy stance for the multiple benefits of CR intervention for this and other minority patient populations. We will provide additional analyses of cross-sectional racial differences in future reports as we accumulate data from a larger number of minority patients.

Normative values for 6MW tests have been published for apparently healthy younger¹⁸, ¹⁹ and older⁴⁰, ⁴¹ people aged 20 to 80 years. To our knowledge, norms have not been published for CR patients of different age categories. Our study is the first to present mean 6MW scores for a large number of male and female CR participants between the ages of 40 to 89 years, data which may be useful in the development of standards for 6MW tests in CR programs. By providing this information as a “yardstick” for comparisons, patients and staff can determine how one compares with a particular age group or with cardiac patients as a whole.

Effect size 

Basic thresholds for clinically meaningful improvements in physical performance tests for cardiac patients are lacking in the literature. One method of assessing the magnitude of change in one's health status is the effect size—a standardized measure of change within a group. Although the magnitude of the effect size that is clinically relevant for specific health parameters has yet to be established, Cohen⁴² and others²⁰, ²¹, ⁴³ have suggested that an effect size of 0.20 is small, 0.50 is moderate, and 0.80 is large. Thus, the greater the effect size, the stronger the evidence that the change represents a clinically meaningful improvement in a particular variable, such as 6MW distance or quality of life survey scores.

In patients with chronic lung disease, the reported minimal clinically important improvement for the 6MW has been reported to be 54 meters (177.2 ft), with an effect size of 0.49.⁴⁴ Our patients exceeded this level of 6MW performance, with the exception of women aged 50 to 59 and men aged 80 to 89. Overall, moderate to large effect sizes were observed for 6MW improvements in women (range, 0.48 in the 50-59 age group, to 0.81 in the 60-69 age group) and men (range, 0.47 in the 80-89 age group, to 0.70 in the 50-59 age group). The mean increase in 6MW distance for women ranged from 139 ft in those aged 50 to 59 to 229 ft in those aged 60 to 69. The mean increase in 6MW distance for men ranged from 135 ft in the 80 to 89 age category to 250 ft in the 50 to 59 age category. These results are the first to suggest that moderate to large clinically significant improvements in 6MW performance may occur in men and women from multiple programs after short-term outpatient CR participation. Although the effect size may be a useful tool when looking at physical or psychosocial parameters in cardiopulmonary rehabilitation, other more sensitive instruments may help determine clinically meaningful improvements in outcomes measures in future investigations.⁴⁵

QOLI 

Multidisciplinary CR intervention improves quality of life parameters in cardiac patients of all ages with a broad spectrum of cardiac pathologies.¹, ², ³, ⁴, ⁷, ⁸, ⁹, ¹⁰, ²⁹, ³⁹ There is debate on the optimum test instrument and the best method of interpreting quality of life scores in women compared with men because women in CR programs may have more depression, less energy, and lower quality of life scores than men.⁴⁵, ⁴⁶, ⁴⁷, ⁴⁹ Interestingly, many investigators have found little or no relationship between perceived and measured health and function traits in both cardiac⁴⁸, ⁴⁹ and pulmonary⁵⁰, ⁵¹ populations. Our findings concur with these studies because we also found low correlations between the improvement in 6MW scores and improvement in QOL scores. In contrast, Hamilton and Haennel¹¹ found that 6MW performance was moderately correlated with scores from the Physical Function component of the SF-36 Health survey (r = .62; P <.001) in 94 men and women (63 ± 10 years) who participated in short-term, multidisciplinary CR training. Similarly, Bauman and Arthur⁵² noted that in patients with peripheral vascular disease, gains in functional exercise capacity from a timed walking test showed a moderate (r = .57) correlation with the Physical Function component of the SF-36 Health Survey. Other investigators have found strong correlations between health related quality of life measures and 6MW performance in pulmonary patients.²¹

The finding that improvements in the QOLI Health and Function scores did not associate with improvements in 6MW performance was not unexpected on the basis of previous findings and the design of the QOLI. In the QOLI, the domain of Health and Function is quite broad and asks the patient's perception of the following issues: one's own health, health care, chest pain, shortness of breath, energy, independence, control over life, long life, sex life, family duties, usefulness to others, stress, leisure activities, travel, retirement, and lifestyle. Thus, it is possible that the QOLI Health and Function domain and the 6MW test measure 2 distinctive aspects of functional ability. Although showing significant gains in gross functional abilities, CR participants may not appreciate these improvements from a psychosocial perspective after short-term CR. They may still perceive themselves as functioning at a much lower level than before the cardiac event, even though they have improved physically. Morrin et al⁴⁹ found that physical activity levels improved earlier in the CR process, whereas mental health adjustments occurred later in the program. In the multi-site Indiana study,⁸ the greatest improvements in health status were observed in the physical function scores of the SF-36 Health Survey, compared with the other subscales. Again, this may be attributable to physical function improving more readily than other health parameters in the early stages of CR. Additional research is needed to define the relationships between physical and psychosocial improvements in patients of CR programs, looking specifically at patient diagnosis, mental health status (eg, degree of anger, hostility, and depression), sex, and ethnicity.

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Limitations 

There are some important limitations of this investigation that warrant attention. First, this was a prospective, nonrandomized study. We did not include a control group of patients who did not participate in CR for comparative purposes. For a study of this nature, it was nearly impossible to randomize participants from different programs or to develop a control group of nonparticipating CR patients because we had no control of who entered and who did not enter CR programs from different cities and towns. Secondly, because the 6MW test is an imprecise estimate of functional capacity compared with a maximal graded exercise test with measurement of gas analysis, we cannot imply a causal relationship between 6MW improvements and improvements in functional capacity. Direct metabolic measures before and after exercise training are needed to prove this, and indeed, have been shown previously in the literature. Because this outcome has been well-established and widely accepted in cardiac patients, our data reinforces what we already know. We have provided new information by showing the percentage improvement in 6MW performance across programs by age group for both men and women, and if these gains were clinically significant from a practical point of view.

Thirdly, 6MW tests in this investigation were administered only once for each patient during the initial and follow-up visits. Early work with chronic heart and lung disease patients by Guyatt and others¹², ¹⁵, ¹⁶ found a learning effect to be evident over the first 3 6MW tests, suggesting that a minimum of 2 to 3 walks be performed initially to establish a baseline. As a result of time and staff limitations evident in North Carolina CR programs (and programs nationwide), we chose to test all patients only once before and after CR. Although this certainly was not ideal, it was the only feasible option for maximal program participation, given the ever-growing time and staff restraints inherent in most CR programs. Furthermore, this mirrored the protocol of Jungbauer and Fuller⁸ made statewide comparisons easier in the future for the establishment of “one-trial” 6MW norms.

Finally, this was an investigation of relatively short duration—up to 12 weeks. It is now evident that short-term participation in CR only begins a lifetime rehabilitation process for the cardiac patient. Indeed, the benefits of long-term CR participation (≥1 year) on lipids, functional capacity, and body weight suggest that greater efforts should be made to retain patients in a structured multiple intervention program for greater than 12 weeks.⁵³ Once a patient leaves the structured program, he or she often resumes old habits and returns to the CR program with subsequent medical problems related to poor lifestyle choices. This ongoing investigation from the NCCRA will examine the long-term benefits of CR across programs statewide in future reports as follow-up information is gathered.

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Clinical implications 

The process of measuring outcomes, benchmarking results, and using this information to verify the importance of CR intervention will be critical for the success of CR programs in the 21st century. Collecting patient and program outcomes is recommended by both the AACVPR¹ and the Joint Commission on the Accreditation of Hospital Organizations. This information, when collected, analyzed, and reported, documents the progress of patient as well as overall program effectiveness. This study from the NCCRA adds to the growing body of literature showing successful health outcomes after CR in large groups of diverse patients from programs across the country with the use of relatively simple outcomes assessment tools. The 6MW test is an easily administered test that provides reliable and practical measures of functional capacity in a short time period. CR staff can use the 6MW in practice for exercise evaluation, risk stratification, and to assist with individualized exercise interventions. CR staff can also expect clinically significant improvements in 6MW performance after regularly attended CR in both middle-aged and older patients, important information to share with clinic administrators and health care agencies. From these data, norms may be developed by patient age, sex, race, and even diagnosis for benchmark comparisons with affiliate CR societies. Moreover, the 6MW test may have benefits in providing information for individualized exercise prescription for those patients who enter a CR program without an entry graded exercise test. Although improvements in 6MW performance may not relate to improvements in psychosocial and quality of life issues during the early stages of outpatient CR, these issues need additional examination before conclusions can be drawn on how physical and mental health parameters interrelate over time.

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Conclusions 

The following conclusions can be drawn from this ongoing NCCRA investigation:

Additional study of 6MW and QOLI parameters benchmarked with programs from other affiliated societies is needed to strengthen the statistical power showing the positive effects of CR in specific disease populations (eg, congestive heart failure, peripheral vascular disease, diabetes). Comparisons also need to be made with those who do not participate in formalized CR programs to assess the true positive effects of CR intervention in particular disease groups. Finally, ethnic diversity needs to be specifically addressed in studies of outcomes in CR. Research of this nature may facilitate a more thorough understanding of the benefits of CR and provide strong rationale for better reimbursement for the many essential services provided by CR professionals in the treatment of chronic illness in diverse patient populations.

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Acknowledgements 

The authors thank the members of the NCCRA for taking the time and effort to measure, quantify, and submit data for this ongoing investigation. We also thank Dr. Carl King, Dr. Derek McEntee, and Dr. Carol Ferrans for their efforts in the development and refinement of a tool to quantify scores on the Ferrans and Powers QOLI for everyday use in cardiac and pulmonary rehabilitation programs across the country.

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References 

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