The effect of exercises on walking distance of patients with intermittent claudication: a study of randomized clinical trials.

This systematic review (meta-analysis) examines the effect of walking exercises in patients with intermittent claudication due to peripheral arterial occlusive disease (PAOD) in the lower extremities. Peripheral arterial occlusive disease in the lower extremities is diagnosed on the basis of the patient's medical history an physical examination in addition to tests such as Doppler (pulsations) and treadmill tests.[1] Intermittent claudication is characterized by absence of pain or discomfort in a limb when at rest; the commencement of pain, tension, and weakness after walking is begun; intensification of the condition with walking until walking becomes impossible; and the disappearance of the symptoms after a period of rest.[2]

In 1989, Norton and Strube[3] briefly discussed the concept and advantages of a meta-analysis for physical therapy practice in Physical Therapy. Since that time, five meta-analyses[4-8] have been published in this journal.

The prevalence of PAOD in the general population is generally estimated to be between 1% and 3% in men and women over 60 years of age, with the higher prevalence in male patients.[9-11] Criqui et al,[12] however, found in a geographically defined population of 613 men and women (mean age = 66 years) that the prevalence of peripheral arterial large-vessel disease was 11.7% when four highly reliable and noninvasive techniques were used to establish the diagnosis of PAOD. Half of the patients in this cohort were at or above age-and gender-specific 90th percentiles for serum cholesterol concentrations and at or above 95th percentiles for triglyceride concentrations. In a recent study, Stoffers et al[13] found a prevalence of PAOD in the lower extremities of 6.9% (95% confidence interval [CI] = 5.7-8.2) in a stratified sample (n = 3,171; age = 45-74 years) of the total population (N = 18,884) of 18 private practices of general practitioners. The prevalence of intermittent claudication in this population was 6.6% (CI = 5.2-7.9). Because PAOD is age related and as the proportion of people over 65 years of age increases, it can be expected that the prevalence of patients with PAOD will increase.

The annual incidence of intermittent claudication is estimated at approximately 20 per 1,000 in people over 65 years of age.[14] Intermittent claudication affects the patients' daily life and social activities because of their reduced walking range. These effects may have a detrimental influence on the perceived quality of life of these patients. Treatment options include medication, exercises, education about risk factors (eg, diet, smoking), and vascular surgery.[15-19] Selection of interventions depends on the location and severity of the occlusion location and comorbidity. Many patients with limited walking ability are referred to physical therapy departments for walking exercises and other exercise programs. In these walking exercises, the patients usually are encouraged to walk their maximum walking distance, as determined by the onset of pain, several times each day.

The purposes of this article are (1) to report on the effects of walking exercises on the distance that patients with intermittent claudication could walk in randomized clinical trials (RCTs) and (2) to report on the methodological quality of these RCTs.[20-23.]

Method and Materials

Two literature databases were accessed: MEDLINE and the database of the Dutch National Institute of Allied Health Professions (NPi). The NPi database was started in 1987 as a "companion" database to MEDLINE because it was believed that MEDLINE does not contain many publications that are relevant to the field of rehabilitation, including physical therapy. In addition, the NPi database is accessible with key words specific to the field of rehabilitation. For our study, the key words related to the effect of walking exercises on walking distance or time in patients with PAOD. The RCTs should have been in English, German, Dutch, or French. Finally, walking distance or time on a treadmill test should have been used as an outcome measure. The control group could be either an untreated group, including placebo drug treatment, or a group with a different intervention.[24,25] The MEDLINE search provided us with 13 reports of RCTs, and the NPi database provided us with 16 reports. By screening the reference lists, another 53 reports were identified.

Two reviewers (JWB and BGR) studied the articles, which were "blinded" for author(s) and journal. In addition, the reviewers were not provided with the list of references of each study. One reviewer is a physician with a background in cardiac and vascular rehabilitation. The other reviewer is a physical therapist with no experience in this field.

Prior to studying the articles, a checklist that was specific for this patient group was developed. The checklist was developed for use by the two reviewers to extract, independent from each other, relevant information and data from the reports and subsequently to assess whether there is agreement. The checklist was evaluated several times for completeness and was modified after two articles were studied and discussed. A second physical therapist and a vascular surgeon who were experts in the field were involved in the development of the checklist. The checklist contained several hundred items relating to gait and treadmill characteristics, vasoactive medication, comorbidity, cointerventions, follow-up, localization of occlusion or stenosis, and diagnostic procedures.

To assess the methodological quality of the RCTs, a list of items was used; this list was based on the list originally proposed by Chalmers et al[20] and modified by Bouter[23] (Tab. 1). Weighting of the items within each domain was based on consensus. The total methodological quality score that could be obtained was 100. The methodological quality score could be calculated, based on the checklist.

[TABULAR DATA 1 NOT REPRODUCIBLE IN ASCII]

Results

After applying the inclusion criteria to the identified RCTs, 21 reports[26-45] qualified for the analysis. The reviewers agreed to eliminate 11 reports[26-36] for further analysis after preliminary reading because the patients were not randomly assigned, the studies were duplicate studies, or the authors had not made use of a treadmill or did not report on the effect of exercises on walking distance. Thus, only 10 reports[29,37-45] were left for the analysis. Two studies[44,45] involved the same subjects, but different outcome variables were used. We decided, therefore, to analyze both studies.

The literature search also provided us with two review articles[46,47] and a meta-analysis.[48] These articles were given to the reviewers at the end of their analysis so that the results and conclusions of these studies would not influence their findings.

Table 2 lists important characteristics of the patients and the treadmill protocols. In three studies, only men were included. In the remaining studies, the proportion of men was at least 75%. Group sizes were relatively small; there were 25 subjects in one study and fewer than 20 subjects in the remaining studies. Five of the studies had an untreated control group. In the remaining studies, the other experimental groups had surgery (percutaneous transluminal angioplasty) or received medication.

[TABULAR DATA 2 NOT REPRODUCIBLE IN ASCII]

Important differences were also observed in the maximum walking distances prior to the studies and in the treadmill protocols. Differences in walking distances can indicate the severity of the disease and the "intensity" of the treadmill test.

Table 3 gives the important characteristics for the exercise program and the effect of the intervention. As noted in Table 3, "walking only" or treadmill exercise was part of a few studies. Furthermore, there was a wide variety in intensity, duration, and contents of exercise programs. Improved walking performance was assessed as improvement in pain-free or maximum walking distance or time.

[TABULAR DATA 3 NOT REPRODUCIBLE IN ASCII]

The overall improvement in walking distance or time and the duration of the treatment program are also shown in Table 3. Percentage of change is given as provided in the articles or as we calculated from the data or figures in the reports. Percentage of improvement in walking distance or time ranged from 28% to 210% (X = 105%, SD = 55.8%). Despite the differences in patient samples and exercise programs, all studies showed a positive effect for walking exercises. In Table 4, the methodological quality score for each study is given. The scores for methodological quality of the studies ranged from 47 to 75 (X = 62.5, SD = 8.5). The median score was 61.

[TABULAR DATA 4 NOT REPRODUCIBLE IN ASCII]

Discussion

In a qualitative meta-analysis, the RCTs are preferably analyzed in a "blinded" manner. Depending on the nature of the study and the knowledge of the reviewers, for the reviewers to be truly "blinded" required that they scan the articles and then print the articles in a uniform style, leaving out names, references, and other details within the text by which the authors or place of study could be identified. An expert reviewer, however, may recall the study and may know the investigator and where the study was conducted. For our study, we used "differential photocopying," which means that only authors' names, journal name, and references were deleted.[20]

In most studies, we could not determine whether the researchers were "blinded" with respect to assignment of the patients to experimental and control groups (Tab. 4, column N). There was a large interval between the lowest and highest scores (ie, 47 versus 75). We noted a trend for the quality of the studies to improve over time, with the most recent studies having higher methodological quality scores. For some of the studies, the randomization procedure was not stated, and, therefore, we could not determine whether the procedure was correct. Only reports that stated that subjects had been randomly assigned were included in our analysis.

In our study, we did not calculate the overall effect size by pooling the data. Some authors[49] believe that statistical pooling should be considered only when the control and intervention groups are homogeneous, the interventions are comparable, and the studies are of good methodological quality.

Gardner and Poehlman[48] pooled data in their meta-analysis (n=21). In their study, the articles were not blinded and the methodological quality of the studies was not assessed. The study by Gardner and Poehlman included 9 of our original 21 studies and 5 of the 10 studies in our analysis. They reported that the mean walking distance increased from 125.9 m (SD=57.3) to 325.8 m (SD=148.1), a mean increase of 179%. the discrepancy between the number of studies reviewed by Gardner and Poehlman and those included in our study can be explained by the fact that controlled clinical trials were permitted in the study by Gardner and Poehlman, whereas in our study an inclusion criterion was that the study should be randomized. From the start of our study, therefore, numerous studies were eliminated because they were not randomized. In addition, other studies were part of our analysis because languages other than English could be included. Finally, a few more reports have been published since the study by Gardner and Poehlman.

The effects of the different studies, as reported in this article, cannot be compared because outcome measures (walking distance or time), interventions, and treadmill tests (speed and slope) varied. Each of the "randomized" studies that we analyzed, however, demonstrated a positive effect on walking distance or time in spite of the heterogeneity and differences in demographic data, exercise variables, and walking distances or times among the different studies. Taken together with the small sizes of the experimental and control groups, however, we believe that the uniform positive effects of an exercise program are very supportive of the beneficial effects of such interventions for patients with intermittent claudication.

Lundgren et al[40] reported that all patients in their study benefited equally from the exercise program and that there was no relation between their improvements and age, gender, history of myocardial complaints, diabetes, and level of stenosis. The meta-analysis by Gardner and Poehlman,[48] however, revealed that age was correlated with increases in walking distances.

In one study,[38] the true magnitude of the effect of exercise training could not be established because, as the authors admitted, the patients in the control group had started to exercise as well. Only a few studies demonstrated lasting effects after the study period was completed.[41,50,51]

Hiatt et all[44] have shown that a 6-month supervised exercise program further increased the benefit of treatment as compared with a program that lasted only 3 months. Creasy et al[41] showed that there was further improvement at 9 months following a formal exercise program of 6 months' duration.

In the study by Lundgren et al,[40] the possible additional effect of exercises in patients who had vascular surgery was investigated. It appeals from their study that exercises may enhance the benefits of surgical interventions. The study by Lundgren et al, however, lacked a long-term follow-up, and the intensity of the exercise program was low. The indications for vascular intervention and the timing and type of vascular intervention remain important areas for further research. In a study by Williams et al,[51] 38 out of 68 patients who were enrolled in a vascular rehabilitation program that included monitored exercise sessions, education with respect to risk factors, and a home exercise program continued to have intermittent claudication after completion of the program. The authors did not break down the results, comparing patients who had undergone vascular surgery and patients who had not undergone vascular surgery. The overall mean improvement in walking distance was 149% at 1 year and 178% at 2 years. In a multicenter (n=18), multinational (the Netherlands, Great Britain) prospective study,[52] researchers are currently investigating the indications for and effects of various surgical techniques for patients with intermittent claudication.

The authors of the two review articles[46,47] and the meta-analysis[48] reached similar conclusions: walking exercises improve the pain-free walking distance of patients with intermittent claudication. The authors of the meta-analysis (21 studies) concluded that most improvement in walking distance is obtained when the duration of the exercise program is more than 30 minutes with a minimum of three exercise sessions per week, when walking is the mode of exercise, and when the program duration is longer than 6 months. Patients should be exercising to, or near, the point of maximum pain. The data presented in Table 3 seem to support the relationship between the duration and intensity of an exercise program and improvements in walking distance.

Conclusion

All studies that met our inclusion criteria showed that walking exercises have a positive effect on walking distance. If an increase in walking time is reported, an increase in walking distance may be assumed. Because many studies showed methodological flaws (eg, small group size, lack of heterogeneity of groups, comorbidity), additional studies are warranted to further substantiate the beneficial effects of walking exercises for patients with intermittent claudication. We therefore recommend (1) that further research should be started to determine the ideal exercise regimen for patients with intermittent claudication (eg, duration, frequency, intensity, type of exercises), (2) that additional research should be conducted to determine when maximum gains in pain-free walking distances are achieved and at what level an exercise program should be maintained to prevent a decrease in walking distance, and (3) that patients' well-being and quality of life should be taken into consideration as an outcome measure. Only the recent study by Regensteiner et al[45] focused to some extent on outcomes related to patients' well-being and quality of life.

References

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[10] Jelnes R, Gaardsting O, Jensen KH, et al. Fate in intermittent claudication: outcome and risk factors. BMJ. 1986;293:1137-1140.

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[13] Stoffers HEJH, Rinkens PELM, Kestre ADM, et al. The prevalence of asymptomatic and unrecognized peripheral arterial occlusive disease. Int J Epidemiol. 1996;25:282-290.

[14] Kannel WB, McGee DL. Update on some epidemiologic features on intermittent claudication. J Am Geriatr Soc. 1985;33:13-18.

[15] Lindgarde F, Jelnes R, Bjorkman H, et al. Conservative drug treatment in patients with moderately severe chronic occlusive peripheral arterial disease. Circulation. 1989;80:1549-1556.

[16] Taylor LM, Porter JM. Proposed design for a double-blinded trial to evaluate medications for treatment of intermittent claudication. J Vasc Surg. 1992;15:882-884.

[17] Holm J, Arfvidsson B, Jivegard L, et al. Chronic lower limb ischemia: a prospective randomised controlled study comparing the 1-year results of vascular surgery and percutaneous transluminal angioplasty (PTA). Eur J Vasc Surg. 1991;5:517-522.

[18] Ahn S, Rutherford RB. A multicenter prospective randomized trial to determine the optimal treatment of patients with claudication and isolated superficial femoral artery occlusive disease: conservative versus endovascular versus surgical therapy. J Vasc Surg. 1992;5:889-891.

[19] Andriessen MPHM, Barendsen GJ, Wouda AA, DePater L. Changes of walking distance in patients with intermittent claudication. Vasa. 1989;18:63-68.

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[23] Bouter LM. Meta-analyze: Controleerbaar en Reproduceerbaar Literatuuronderzoek als Basis Voor Rationele Beslissingen in de Gezondheidszorg. Amsterdam, the Netherlands: Amsterdam University Press; 1994.

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Invited Commentary

The article by Brandsma and colleagues provides a systematic review of 10 randomized clinical trials that assessed the effect of an exercise program on the walking tolerance of patients with intermittent claudication (IC). The results are unequivocal: Walking exercises improve walking distance or walking time for patients with IC. The percentage of improvement in walking distance or time ranged from 28% to 210%, with an average of 105%. In another meta-analysis reviewing the same topic, Gardner and Poehlman[1] reported that the mean walking distance until the onset of claudication pain increased 179% (from 126 [+ or -] 57 m to 351 [+ or -] 189 m) following an exercise program that included walking. These results are strong evidence that walking exercise can have a large and meaningful impact on the ability to walk for patients with IC.

Every study showed meaningful improvements in walking tolerance following a walking exercise program, and the authors in every study recommended that exercise should be part of the conservative treatment for patients with IC. General guidelines for exercise, as reported by Brandsma et al and by Gardner and Poehlman,[1] are as follows: participants should exercise at least 30 minutes a session, with a minimum of three exercise sessions per week, for (ideally) at least 6 months. Exercise programs in which only walking was performed had better outcomes than exercise programs that contained walking and other forms of exercise.[1] Greater improvements were associated with longer training times. According to the results of these studies, patients should be encouraged to exercise to, or near, the point of maximum claudication pain. Apparently all studies reviewed by Brandsma et al contained a structured exercise program at an institution (Tab. 3). In the meta-analysis by Gardner and Poehlman,[1] 19 of the 21 reviewed studies included a structured exercise program at an on-site facility with "trained personnel supervising the exercise session."

These results are alarming to me because it is my impression, and that of other authors,[2] that the current management of patients with IC often does not include the exercise program described above. Although I am unaware of data on the number of patients with IC who are treated with a walking program on an outpatient basis, a recent study conducted in the United Kingdom[3] outlined the high levels of inpatient costs and morbidity for treating patients with peripheral vascular disease, infection, neuropathy, and ulceration. Approximately 20% of the hospital admissions for this population included a surgical procedure, and the total cost of treatment for primary diagnoses in these categories during a 4-year period wa estimated at $9,743,855. Although 19 different surgical procedures were described, there was no mention of exercise or rehabilitation.

Despite the encouraging results from Brandsma and colleagues' and Gardner and Poehlman's[1] review articles on the benefits of exercise for patients with IC, it seems that most patients with IC are not referred for physical therapy and are not provided with a structured walking program. Although patients may be told informally by their physician to "walk more," they are not provided with specific instructions or with a structured format to conduct these exercises. The result often seems to be that they show no improvement, their condition deteriorates, and they may go on to require more invasive treatment, including vascular reconstructive surgery and even amputation.[3] Due to the documented outcome, the cost, and the possibility of complications,[3] a specific exercise program seems like critical treatment for every patient with IC, especially early in the disease process. Although a walking program clearly has been shown to improve the walking distance of patients with IC, long-term studies are needed to determine whether a walking program can also help delay or prevent future complications.

A walking exercise program has clear benefits for many patients with IC, but physical therapists should be mindful of a number of precautions, especially in patients with IC and diabetes mellitus (DM). After 20 years' duration of DM, the prevalence of peripheral vascular disease is approximately 45%.[4] Intermittent claudication is associated with a threefold to fourfold increased risk of coronary heart disease, stroke, or cardiac failure in women with DM and a two to three times higher risk of these complications in men with diabetes.[4] In addition, many patients with peripheral vascular disease and DM will have peripheral sensory neuropathy. Patients who have peripheral neuropathy (ie, as demonstrated by inability to sense the 5.07 Semmes-Weinstein mono-filament on the bottom of their foot) are at high risk for skin breakdown on the foot fro weight-bearing activities such as walking or running.[4,5] These patients should perform bicycling or swimming exercises, which do not stress the foot as much as walking.[5] Although these exercises may not improve walking ability as much as a walking exercise,[1] they should help to prevent skin breakdown.[5]

Despite these precautions, this article provides strong evidence for the benefits of a walking program for patients with IC. Given this strong evidence for the benefits of walking exercise for patients with IC, why are there not more of these programs? The procedures are not difficult. Although more research is needed to refine exercise guidelines, general guidelines are established. Will third-party payers reimburse such treatment? Costs associated with complications of peripheral vascular disease are high,[3] and I believe that third-party payers will reimburse if we can show that such an exercise program will delay or prevent future complications, costly surgery, and hospitalization. The data from the studies in this meta-analysis would suggest a cost benefit from exercise, but specific research that includes cost analysis is needed. Is adherence to an exercise program difficult? Adherence to an exercise program appears to be difficult in this population,[2] just as adherence to an exercise program is difficult in other patient groups with chronic disease, including patients with obesity, elderly patients, and patients with non-insulin-dependent diabetes.[6] Given the documented benefits of exercise, more research is needed to improve exercise adherence.

In this period of "evidence-based practice" and increasing demands from third-party payers to justify our treatment, physical therapists should jump at the opportunity to be more involved in providing structured exercise programs for patients with IC. This clearly is an area where we can make an important and meaningful change in the status of patients with severe disability.

I believe the results of this review are unequivocal and, therefore, I have focused on the implications of this study rather than on methodological issues. Because the authors of this report are a multidisciplinary team, including several physical therapists and a vascular surgeon, I would ask them to elaborate further on the implications of their research and practice and on how physical therapists in the United States (and elsewhere) might be more successful in establishing successful walking exercise program for patients with IC. I thank the authors for submitting this important work to Physical Therapy, and I thank the Editor for providing me the opportunity to comment on it.

References

[1] Gardner Aw, Poehlman ET. Exercise rehabilitation programs for the treatmnt of claudication pain: a meta-analysis. JAMA. 1995;274: 975-980.

[2] Ernst E, Fialka V. A review of the clinical effectiveness of exercise therapy for intermittent claudication. Arch Intern Med. 1993;154:2357-2360.

[3] Currie CJ, Morgan CL, Peters JR. The epidemiology and cost of inpatient care for peripheral vascular disease, infection, neuropathy, and ulceration in diabetes. Diabetes Care. 1998;21:42-48.

[4] Diabetes 1993: Vital Statistics. Alexandria, Va: American Diabetes Association; 1993:26.

[5] American Diabetes Association. Position Statement: Diabetes Mellitus and Exercise. Diabetes Care. 1998;21:S40-S46.

[6] Clark DO. Physical activity efficacy and effectiveness among older adults and minorities. Diabetes Care. 1997;20:1176-1182.