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Home » Use of the 6-Min Walk Test: A Pro and Con Review

Use of the 6-Min Walk Test: A Pro and Con ReviewPCCSU Article | 06.15.09

By Daniel R. Smith, MD, FCCP

Dr. Smith is Assistant Professor, National Jewish Medical and Research Center, Denver, CO.

Dr. Smith has disclosed no significant relationships with the companies/organizations whose products or servicesmay be discussed within this chapter.

Objectives

1. Review the history of the development of functional testing.

2. Review indications for exercise testing.

3. Review the appropriate methodology for 6-min walk testing.

4. Understand the use of 6-min walk testing as a prognostic test.

5. Understand the use of 6-min walk testing as a method of determining the effectiveness of therapeutic interventions.

Key words: 6-min walk; exercise; functional assessment

Abbreviations: 6MWD = 6-min walk distance; 6MWT = 6-min walk test

The 6-min walk test (6MWT) has been widely used and accepted as a simple, cost-effective means of clinicallyassessing the functional status of patients with cardiopulmonary diseases and other disorders. Essentially, this testrelies on the basic parameter of total distance walked during a specified time. This relatively low-technology andeasily performed test remains a standardized tool in both clinical and research settings despite the availability ofmore sophisticated physiologic testing. The 6MWT has proven reliable in providing reproducible data to serve as

measures of preand posttreatment comparisons,1-6 in the assessment of functional status,7-9and in predicting

morbidity and mortality for various disease states.2,10-13 Despite the widespread use of 6MWT in various settings,many clinicians are unfamiliar with the specifics regarding proper testing and accepted standards for the use of thismeasure. This paper will briefly review the history of and guidelines for the 6MWT and provide a pro/condiscussion of its use.

Distance testing was first advocated by Balke14 in 1963 as a means of assessing physical fitness. Kenneth H.

Cooper15 later used a 12-min walk/run test in healthy Air Force personnel that demonstrated a strong correlationwith maximal oxygen consumption, as obtained on maximal exercise testing on a treadmill, as well as the ability to

detect changes in conditioning. McGavin16 made additional modifications to the test in 1976, as he used a walk testto assess disability in patients with COPD. Subsequent work determined the effectiveness and reliability of shorter-distance walk testing and, eventually, the 6-min time became the most widely accepted protocol. The 6MWT is asubmaximal, self-paced test that is currently used to assess functional capacity in various settings.

In 2002, the American Thoracic Society (ATS) outlined specific guidelines regarding the background and use of the

6MWT and methodology for performing the test.17 This invaluable reference reviewed the concept of functionaltesting as a means of assessing the global and integrated physiologic responses to exercise, rather thanspecifically measuring the function of individual organ systems. Accepted indications (Table 1) andcontraindications for 6MWT were outlined with recommendations to address safety issues related to testing.Technical aspects of testing that were reviewed included performing the test indoors along a straight, flat corridorwith a hard surface. A 30-m distance course was specified, and turnaround points were identified with traffic conesand 3-m interval measurements well marked with colored tape on the floor. Recommendations also were specifiedfor required testing equipment, patient preparation, and detailed instructions for performing the testing. Subjective

patient dyspnea assessments are to be obtained pre- and posttesting using the Borg scale.18 The ATS referencealso addressed the need for standardized pretest patient instructions and specified scripted verbal interactions attimed intervals during testing to eliminate the possibility of coaching or encouragement effects. Guidelines weresuggested to limit controllable factors for variability, address the potential use of practice tests, and outlinestandardized testing for patient use of oxygen and/or medications prior to or during testing. Finally, the ATS paperreferenced studies regarding the interpretation of 6MWT results before and after interventions and recommendedthat changes in 6-min walk distance (6MWD) be expressed by absolute value. Values for statistically significant

changes in 6MWD for groups and individuals were referenced from the work of Redelmeier and colleagues.19 Theuse of single 6MWT values as a measure of the functional status of individuals was not recommended with therecognition of the lack of adequate standardized normal values.

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Use of the 6-Min Walk Test: Pros

Perhaps the best rationale for use of the 6MWT lies in the practicality and simplicity of the test itself. The 6MWT is acost-effective procedure that may be performed in nearly any clinical location without the need for either directphysician involvement or invasive, and often expensive, monitoring equipment. As a self-paced and submaximalexercise procedure employing the familiar activity of walking, the 6MWT is well tolerated by patients over a widespan of fitness levels and debility. The 6MWT, in comparison to other functional walking tests, is also felt to offeradvantages that include established standards for testing, reference values, and correlation with the capacity to

perform activities of daily living.6,20 The safety of 6MWT is ensured by adherence to specific ATS guidelines17

regarding contraindications for testing, and it has been confirmed by two large studies.7,21

The 6MWT is, importantly, a measure of functional exercise performance that reflects the integrated and globalresponses of multiple factors involved in exercise. The 6MWT may demonstrate pulmonary dysfunction occurringfrom the combination of dyspnea, airflow limitation, dynamic hyperinflation, and skeletal muscle dysfunctionassociated with COPD. This functional assessment approach reveals not only limitations from cardiopulmonarysystem abnormalities, but also potential contributions, such as changes in peripheral circulation and bloodcomposition, and neuromuscular and muscular metabolic responses. There are recognized and previouslydiscussed advantages in using this comprehensive assessment in defining the severity of disease over simpler

physiologic parameters alone.22,23 Importantly, the objective data from 6MWT allow a functional assessment of

disease outcome and demonstrate less intrasubject variability than subjective questionnaires.24

The 6MWT has been validated using physiologic parameters and quality-of-life measurements. In patients withCOPD, 6MWT results correlate well with maximal oxygen consumption and work rate obtained by bicycle

ergometer testing (r=0.51 to 0.81).6,24-28 The correlation of 6MWT data and maximum oxygen uptake extends to

patients with congestive heart failure, pulmonary hypertension, and pulmonary fibrosis.2,11,29-31 Directcomparisons of 6MWD with dyspnea scores and other quality-of-life measures in COPD patients demonstrate

weaker and more variable correlation.6,28,32 Test-retest reliability of the 6MWT also has been definitively

demonstrated.11,33 The responsiveness of the 6MWT has contributed to the widespread use of the test as anoutcomes measure in assessing the impact of pharmacologic, surgical, and rehabilitative interventions. In patients

with COPD, 6MWT data have demonstrated improvements with interventions such as bronchodilators,34 mucous

clearing devices,35 pulmonary rehabilitation,36 and lung volume reduction surgery.37 C linical studies fornumerous disease processes now routinely use 6MWT data as an endpoint to assess responses to therapy.

The 6MWT data also are used as a reliable prognostic tool. Celli and colleagues13 used 6MWT data as one of fourpredictive factors in their multidimensional grading system to predict mortality in patients with COPD. Additional

studies have used the 6MWT to predict mortality in heart failure10,11 and primary pulmonary hypertension.2,38

Such data also can be invaluable in determining the risks, appropriateness, and timing for major interventionssuch as lung volume reduction surgery (LVRS) and transplantation. As an example, the finding of a 6MWD of 200

m or less is associated with a mortality rate of 84% rate in patients undergoing LVRS.39

Use of the 6-Min Walk Test: Cons

Results of the 6MWT are subject to significant variability with minor and potentially easily overlooked variances in

testing procedures from those specified in the ATS guidelines.17 Minor variations in course layout, patientinstructions, or inadvertent coaching may significantly affect 6MWT. Treadmills should not be used for the 6MWT.The use of supplemental oxygen during testing or the use of various medications prior to testing may potentiallyalter performance and must be standardized and documented for accurate comparisons. The recognition of a“training effect” and subsequent initial improvements in 6MWT results without interventions over the first fewweeks of repeat testing must also be taken into consideration. Finally, the 6MWT is not useful in assessing patientswith normal or high exercise capacities with an observed ceiling effect and resultant inability to detect performanceimprovements.

Results of the 6MWT do not always correlate well with other measurements of disease severity. Correlation of

6MWT results with pulmonary function testing in patients with COPD is generally weak (r=0.17 to 0.55),25,28,32

and their 6MWD can be minimally reduced despite severe COPD.6,24,28 A number of factors has been identified as

sources of variability in 6MWD and summarized in Table 2.17 Consideration of these factors should be made whenassessing individual performances and also when comparing results for different populations.

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The use of the 6MWT as a single measurement of the functional status of an individual is inherently problematic.The most widely accepted reference values for normal 6MWD, 576 m for healthy males and 494 m for healthy

females, was based on a study40 with 117 men and 173 women ranging in age from 40 to 80 years. To myknowledge, definitive normal values standardized to more specific patient demographics and using stringent ATSrecommendations do not exist. Reference values and equations commonly used for patients with COPD are based

on a study by Redelmeier and colleagues19 with 112 patients. A low 6MWD finding in a patient is nonspecific andreveals little regarding the various potential factors contributing to the decreased functional status.

The use of the 6MWT as a measure of improvement in functional capacity is widespread in current clinical studies.The determination of what constitutes a significant clinical change as a result of an intervention has been debatedwith generally well-accepted parameters for patients with COPD. The minimal important clinical difference in

patients with COPD is reported to be approximately 55 m for cohorts19,41 and 86 m for individuals.42

Extrapolation of the use of these parameters of minimal important clinical difference to other patient groups maynot be appropriate. In addition, the relative small differences in 6MWD accepted as significant are well within therange of improvement seen with minor variations from ATS guidelines, such as patient encouragement, andunderscore the importance of standardized testing protocols.

The use of the 6MWT has expanded to include applications in predicting morbidity and mortality for various diseasestates. As described above, prognostic data have been generated that use 6MWD to determine the

appropriateness for and timing of surgical interventions, such as LVRS in patients with COPD39 and patients who

undergo lung transplantation for a variety of pulmonary diseases.2 The use of 6MWD in the multidimensional bodymass index, airflow obstruction, dyspnea, and exercise capacity index (BODE) grading system to predict mortality

in patients with COPD13 has been somewhat questioned by subsequent studies43 of patients with more preciselydefined diagnoses of emphysema and severe airflow obstruction. Clearly, more definitive studies are needed toclarify the use of a reliably performed 6MWT for application in clinical settings. Perhaps, prior recommendationsconcerning the use of APACHE II (Acute Physiologic and Chronic Health Evaluation) score data for patients in theICU best summarizes the approach for the use of 6MWT data; paraphrasing Scottish writer Andrew Lang, the datashould be used “as the drunk uses a light post—for support, rather than illumination.”

Conclusions

The 6MWT is a widely used and useful measure of functional status. As with any test, there are advantages anddisadvantages in the application of 6MWT data. Clinicians should be familiar with 6MWT procedures and limitationsgiven the ubiquitous use of this parameter for current clinical studies.

Poststudy Questions

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Related Terms: Pulmonary Function Testing, Bronchoprovocation, and Exercise Testing PulmonaryPhysiology CME PCCSU Volume 23 PCCSU

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