Elsevier

Physiotherapy

Volume 93, Issue 3, September 2007, Pages 175-182
Physiotherapy

Expert article
6-Minute walk test in patients with COPD: clinical applications in pulmonary rehabilitation

https://doi.org/10.1016/j.physio.2007.02.001Get rights and content

Abstract

Pulmonary rehabilitation is an evidence-based intervention for the management of patients with chronic obstructive pulmonary disease (COPD). In clinical practice, the 6-minute walk test (6MWT) is commonly used to assess changes in functional exercise capacity in COPD patients following pulmonary rehabilitation with the primary outcome reported being the distance walked during the test (i.e. 6MWD). The 6MWD has demonstrated validity, reliability after one familiarisation test and the capacity to detect changes following pulmonary rehabilitation. In addition to assessing the outcomes of pulmonary rehabilitation, 6MWD may be used to quantify the magnitude of a patient's disability, prescribe a walking programme, identify patients likely to benefit from a rollator and to identify the presence of exercise-induced hypoxaemia. This review describes the applications of the 6MWD in patients with COPD undergoing pulmonary rehabilitation.

Introduction

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality worldwide [1]. Individuals with COPD develop progressive disability and impairment in quality of life. The disease is associated with high health care costs, of which hospitalisations for exacerbations are a major contributor [2]. There is a scarcity of good prevalence studies that include spirometric measures; however, based on the available literature the prevalence of physiologically defined COPD in adults aged 40 years or above is between 9 and 10% [1]. The prevalence of COPD is projected to increase in many parts of the world as a result of the ageing population and an increase in cigarette smoking [1].

Section snippets

Assessment of functional exercise capacity in pulmonary rehabilitation

Pulmonary rehabilitation is strongly endorsed as an evidence-based intervention for the management of patients with COPD [3], [4]. The benefits of exercise training, the mandatory component of pulmonary rehabilitation, have been convincingly demonstrated [3], [5], [6]. In clinical practice, the 6-minute walk test (6MWT) and the incremental shuttle walking test are commonly used to assess changes in functional exercise capacity following pulmonary rehabilitation with the primary outcome reported

Is the 6MWD a valid measure of exercise capacity in COPD?

The validity of the 6MWD is demonstrated by the moderate to good relationship (r  0.5) between 6MWD and peak oxygen consumption (V˙O2peak) measured during a laboratory-based incremental exercise test to peak work capacity in patients with COPD [12], [13], [14], [15]. The relationship tends to be strongest (r > 0.7) in patients with more severe functional limitation because a self-paced walking test in these individuals more closely represents maximal exercise performance [12], [16]. Examination of

Does 6MWD provide information about physical activity during daily life?

Dyspnoea during activities of daily living is frequently reported by patients with COPD and can result in inactivity and the associated problems of deconditioning and muscle weakness. To the author's knowledge only one study has objectively measured daily physical activity in COPD patients (n = 50) and compared the findings to data obtained in age- and gender-matched healthy controls (n = 25) [17], [18]. Compared to the healthy controls, COPD patients spent significantly less time standing and

Is 6MWD associated with survival?

In patients with severe airflow obstruction, longitudinal data demonstrate that the decline in 6MWD occurs independent of the change in the forced expiratory volume in one second (FEV1) [19]. Further, 6MWD is a stronger predictor of survival than FEV1[19]. This is possibly because 6MWD is influenced by skeletal muscle dysfunction as well as pulmonary impairment and so reflects both the primary pulmonary and secondary systemic manifestations of COPD.

The 6MWD is one of four variables, together

Is 6MWD a useful measure for selecting patients for lung volume reduction surgery or lung transplantation?

Few studies have attempted to determine threshold values of 6MWD for successful outcome following lung volume reduction surgery (LVRS) or for listing patients for lung transplantation. In patients undergoing LVRS, Szekely et al.[23] reported that a 6MWD <200 m (achieved before or after pulmonary rehabilitation) was associated with a high level of mortality 6 months postoperatively (specificity 84%).

In a retrospective review of 145 patients (58 with COPD) who underwent lung transplantation or

Is 6MWD a reliable measure?

The 6MWT requires strict standardisation of the test protocol if reliable data are to be obtained. The factors that influence 6MWD (e.g. track length and course layout, instructions and encouragement, number of tests) and require standardisation have been reviewed in detail elsewhere [25], [26]. A familiarisation effect for the test has been demonstrated with the majority of patients naïve to the test increasing their 6MWD after one familiarisation test and little or no further increase

Is a familiarisation test always necessary?

Where performance on the test is limited by symptoms from co-morbid conditions, for example musculoskeletal or claudication pain, it is reasonable to omit a second test at pre-training assessment. In patients with co-morbid cardiac disease, consideration should be given to terminating the test when heart rate reaches 85% of age-predicted maximal heart rate. Finally, in patients who demonstrate profound oxygen desaturation (SpO2 <80%) during the initial 6MWT, the test should not be repeated

Does a standardised protocol exist for the 6MWT?

In 2002, the American Thoracic Society (ATS) published guidelines for the 6MWT with the aim of providing a standardised approach to test performance [26]. These guidelines however raise some important concerns. Notably, the guidelines state that the use of pulse oximetry is optional and a familiarisation test is not needed in most clinical settings. Failure to monitor oxygen saturation (SpO2) raises safety concerns as a proportion of patients with moderate to severe COPD demonstrate significant

Can a patient's 6MWD be referenced to a ‘normal’ 6MWD?

In recent years there has been interest in expressing an individual's 6MWD as a percentage of their predicted 6MWD in an attempt to quantify the magnitude of a patient's disability. Several reference equations are available for this purpose [31], [42], [43], [44], [45]. The amount of variance in 6MWD explained by these equations ranges from 19 to 66% with most reporting that age, height, weight and gender are significant contributors to 6MWD. The weighting of gender as a contributor,

6MWD as an outcome of pulmonary rehabilitation: what is the minimum clinically important difference (MCID)?

The 6MWD has been shown to be responsive to change following pulmonary rehabilitation [7]. The 6MWT is unique among walking-based tests of exercise capacity in that it is self-paced and allows patients to rest in the event that dyspnoea becomes intolerable. Therefore, patients with severe disability can increase their 6MWD by walking faster or reducing the number or duration of rest periods. In contrast, patients with a high pre-training 6MWD, for example a 6MWD of 600 m implies an average

What percentage of patients achieve the MCID for the 6MWD following pulmonary rehabilitation?

When a standardised 6MWT protocol that includes a familiarisation test at pre-training assessment is utilised, the average improvement in 6MWD following pulmonary rehabilitation is below the 54 m threshold [7], [52], [53], [54] with studies showing that only approximately one third of patients improve their 6MWD by 54 m [55] although the mean change reported exceeds the lower 95% CI of 37 m [7], [52], [53], [54], [55]. In contrast, studies that have failed to standardise the 6MWT protocol or

How can a walking programme be prescribed using 6MWD?

Clinical recommendations for exercise training in COPD patients include a component of high intensity, greater than 60% peak exercise capacity, lower limb endurance training with the aim of eliciting some physiological training effects [3], [56]. To achieve this, ground-based or treadmill walking and cycling are the commonest exercise modalities used.

In practice, many patients can tolerate training at intensities well in excess of 60% peak exercise capacity especially during ground-based

How can the 6MWD be used to select individuals likely to benefit from a rollator?

Patients with COPD frequently report less dyspnoea when pushing a shopping trolley because the trolley enables the patient to adopt a forward lean position and to fix their shoulder girdle, a position that many patients with COPD spontaneously adopt in an attempt to gain relief from dyspnoea. This position is associated with improved inspiratory muscle function, due to the more favourable position of the diaphragm, and facilitates recruitment of the pectoral muscles to assist rib cage elevation

Can the 6MWT be used to identify exercise-induced hypoxaemia?

Monitoring of SpO2 is commonly performed in patients with COPD undergoing supervised exercise training and the data used to assist with determining safe guidelines for exercise prescription. Several studies have shown that the 6MWT, in common with the incremental shuttle and other walking tests, is more sensitive than a symptom-limited incremental cycle ergometry test for detecting exercise-induced hypoxaemia in patients with COPD [15], [40], [69], [70], [71]. The underlying mechanisms for this

Is 6MWD useful in acute exacerbations of COPD?

A low 6MWD (≤367 m) has been associated with an increased risk of admission for an acute exacerbation of COPD [72] thus 6MWD may have a role in assisting in prioritising patients for exercise training.

The 6MWT is appropriate for assessing patients recovering from an acute exacerbation of COPD as such individuals generally have poor exercise tolerance and require frequent rests when walking. Once the patient's condition is stable, the test can be used to diagnose the presence of oxygen

Conclusion

This review has highlighted the clinical applications of 6MWD in patients with COPD undergoing pulmonary rehabilitation. Future research and clinical experience are likely to further refine these applications and identify new applications of the 6MWD in patients with COPD undergoing pulmonary rehabilitation.

Acknowledgements

My sincere thanks go to Nola Cecins MSc, Pulmonary Rehabilitation Physiotherapist for her commitment to the ongoing development of the pulmonary rehabilitation programme at Sir Charles Gairdner Hospital (Perth, Western Australia) over the last 9 years, her contribution to the preparation of this manuscript and for ongoing collaboration in research. I also thank the following clinical and research colleagues, Dr. Peter Eastwood, Dr. Kylie Hill and Joanne Cockram MSc. Finally, I am indebted to

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