Six-minute walk distance in patients with chronic obstructive pulmonary disease: Which reference equations should we use?

Functional capacity using sit-to-stand tests in people with chronic obstructive pulmonary disease and its relationship with disease severity-a cross-sectional study with matched controls

BACKGROUND

Functional capacity impairment is a crucial consequence of chronic obstructive pulmonary disease (COPD). Although it can be identified with simple tests, such as the sit-to-stand tests, its prevalence, relation with disease severity, and the characteristics of people presenting this impairment remain unknown.

OBJECTIVE

To explore the functional capacity of people with COPD.

METHODS

A cross-sectional study with people with COPD and age-/sex-matched healthy controls was conducted. Functional capacity was assessed with the 5-repetitions (5-STS) and the 1-minute (1-minSTS) sit-to-stand tests. People with COPD were grouped according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classifications. Comparisons between people with COPD and healthy controls, and among GOLD groups were established. Associations between symptoms, muscle strength, quality of life, and measures of functional capacity were explored.

RESULTS

302 people with COPD [79% male; mean (SD) 68 (10) years old] and 304 healthy controls [75% male; 66 (9) years old] were included. 23% of people with COPD presented impairment in the 5-STS and 33% in the 1-minSTS. People with COPD from all GOLD classifications presented significantly lower functional capacity than healthy controls (5-STS: COPD median [1st quartile; 3rd quartile] 8.4 [6.7; 10.6] versus healthy 7.4 [6.2; 9.3] s; 1-minSTS: COPD 27 [21; 35] vs healthy 35 [29; 43] reps). Correlations with symptoms, muscle strength, and quality of life were mostly weak (5-STS: rs [-0.34; 0.33]; 1-minSTS: rs [-0.47; 0.40]).

CONCLUSION

People with COPD have decreased functional capacity independently of their GOLD classifications. The prevalence of functional impairment is 23-33%. Because impaired functional capacity is a treatable trait not accurately reflected by other outcomes, comprehensive assessment and management is needed.

Determinants and reference values of the 6-min walk distance in the general population-results of the population-based STAAB cohort study

AIMS

The 6-min walk test is an inexpensive, safe, and easy tool to assess functional capacity in patients with cardiopulmonary diseases including heart failure (HF). There is a lack of reference values, which are a prerequisite for the interpretation of test results in patients. Furthermore, determinants independent of the respective disease need to be considered when interpreting the 6-min walk distance (6MWD).

METHODS

The prospective Characteristics and Course of Heart Failure Stages A-B and Determinants of Progression (STAAB) cohort study investigates a representative sample of residents of the City of Würzburg, Germany, aged 30 to 79 years, without a history of HF. Participants underwent detailed clinical and echocardiographic phenotyping as well as a standardized assessment of the 6MWD using a 15-m hallway.

RESULTS

In a sample of 2762 participants (51% women, mean age 58 ± 11 years), we identified age and height, but not sex, as determinants of the 6MWD. While a worse metabolic profile showed a negative association with the 6MWD, a better systolic and diastolic function showed a positive association with 6MWD. From a subgroup of 681 individuals without any cardiovascular risk factors (60% women, mean age 52 ± 10 years), we computed age- and height-specific reference percentiles.

CONCLUSION

In a representative sample of the general population free from HF, we identified determinants of the 6MWD implying objective physical fitness associated with metabolic health as well as with cardiac structure and function. Furthermore, we derived reference percentiles applicable when using a 15-m hallway.

Reference values for six-minute walk distance and six-minute walk work in Caucasian adults

RATIONALE

The six-minute walk test (6MWT) is a practical and simple field-based test to assess physical capacity. Several reference equations for six-minute walking distance (6MWD, m) exist, but have a number of limitations that decrease their clinical utility. In addition, no reference equations exist for the 6MWT-derived outcome six-minute walk work (6MWORK, kg.m).

OBJECTIVES

To establish new reference equations for 6MWD and 6MWORK on a 20 m course using data from the population-based Canadian Cohort Obstructive Lung Disease study.

METHODS AND MEASUREMENTS

A total of 335 participants without obstructive or restrictive pulmonary function, with normal self-reported health status, normal exercise capacity, and <30 pack years cigarette smoking history were selected to create a representative sample of Canadian adults aged ≥40 years. All participants performed two 6MWTs. Reference equations were derived using multiple regression analyses.

MAIN RESULTS

On average, 6MWD and 6MWORK were 541±98 m and 41.3 ± 11.2 kg.m, respectively. All outcomes were significantly greater in males than females. Sex-specific reference equations were derived from the results of 6MWD and 6MWORK with an explained variance of 24 to 35%.

CONCLUSIONS

This study established reference equations for 6MWD and 6MWORK on a 20 m course in Caucasian males and females aged ≥40 years with normal pulmonary function, self-reported health status and exercise capacity. These newly derived reference equations add value to the assessment of functional capacity in clinical practice.

The Non-Paced 3-Minute Sit-to-Stand Test: Feasibility and Clinical Relevance for Pulmonary Rehabilitation Assessment

Pulmonary rehabilitation (PR) improves health-related quality-of-life (HRQoL) in individuals with chronic obstructive pulmonary disease (COPD), notably by increasing exercise tolerance. Easy-to-implement sit-to-stand tests can facilitate the assessment of exercise tolerance in routine practice. This retrospective study conducted in a real-life setting was designed to describe the non-paced 3-min sit-to-stand test (3-STST) and to evaluate its relationship with HRQoL (VQ11 questionnaire) to identify the determinants of 3-STST performance and to analyze the evolution of 3-STST performance and HRQoL over the course of a community-based PR program. Seventy-one COPD patients (age 69 ± 10 years old; 51% with GOLD spirometric stages III-IV) were included. Mean ± SD 3-STST performance at the initial PR assessment was 43 ± 15 repetitions. This performance was significantly associated with HRQoL and other indicators of clinical severity (lung function, dyspnea, and functional capacities). During the multivariate analysis, younger age, exertional dyspnea with mMRC ≤ 1, and better HRQoL were significantly associated with better 3-STST performance. From the initial to second PR assessment, changes in 3-STST performance were significantly associated with changes in HRQoL. This study provides evidence that the non-paced 3-STST is feasible and might be clinically relevant in the assessment of patients with COPD referred for community-based PR. This test deserves to be prospectively validated.

Obesity, Preserved Ejection Fraction Heart Failure, and Left Ventricular Remodeling

Owing to the overwhelming obesity epidemic, preserved ejection fraction heart failure commonly ensues in patients with severe obesity and the obese phenotype of preserved ejection fraction heart failure is now commonplace in clinical practice. Severe obesity and preserved ejection fraction heart failure share congruent cardiovascular, immune, and renal derangements that make it difficult to ascertain whether the obese phenotype of preserved ejection fraction heart failure is the convergence of two highly prevalent conditions or severe obesity enables the development and progression of the syndrome of preserved ejection fraction heart failure. Nevertheless, the obese phenotype of preserved ejection fraction heart failure provides a unique opportunity to assess whether sustained and sizeable loss of excess body weight via metabolic bariatric surgery reverses the concentric left ventricular remodeling that patients with preserved ejection fraction heart failure commonly display.

Weight-based reference equations for the 6-min walk test can be misleading in obese patients

A 79-year-old female presented to a hospital-based laboratory for pulmonary function testing and a 6-min walk test (6MWT). The patient's chief complaint was dyspnoea on exertion. The patient was a life-long nonsmoker with a history of interstitial lung disease and morbid obesity (body mass index (BMI) 44.9 kg·m⁻²). The patient's baseline spirometry data were within normal limits but the diffusing capacity was moderately reduced (50% of predicted; z-score −4.05) [1, 2].

Weight-based reference equations for the 6-min walk test can produce normal results despite poor performance. Using ideal body weight- or non-weight-based reference equations for the 6-min walk test may produce more clinically meaningful results.https://bit.ly/2wE9Sdn

Using 6-Min Walk Distance Expressed as a Percentage of Reference to Evaluate the Effect of Pulmonary Rehabilitation in Elderly Patients With Interstitial Lung Disease

PURPOSE

The aim of this study was to investigate the effect of outpatient pulmonary rehabilitation (PR) program and the use of 6-min walk distance (6MWD), expressed as a percentage of the predicted value (%6MWD), to quantify response to PR in elderly patients with interstitial lung disease (ILD).

METHODS

This was a prospective, nonrandomized controlled study. Forty eligible patients with stable ILD (≥65 y old) were advised to attend an outpatient PR program for 3 mo. Thirteen patients completed the PR program and formed the PR group. Ten patients who did not attend the PR program were evaluated after 3 mo and formed the control group. Patients in the PR group underwent a comprehensive 3-mo hospital-based outpatient PR program, consisting of educational support and supervised exercise training, and attended the rehabilitation unit weekly.

RESULTS

Change in the absolute 6MWD (Δ6MWD) in the PR group was not significantly different compared with the control group (P = .062). Change in %6MWD (Δ%6MWD) was greater in the PR group than in the control group. Baseline 6MWD was not correlated with Δ6MWD, but baseline %6MWD was significantly correlated with Δ6MWD and Δ%6MWD.

CONCLUSION

PR had a beneficial effect on elderly patients with ILD in terms of exercise endurance. %6MWD might be more useful than the absolute 6MWD as an outcome measure of PR and as a predictor of response to PR in elderly patients with ILD.

Exercise-based evaluations and interventions for pulmonary hypertension with connective tissue disorders

INTRODUCTION

Exercise intolerance is a common and often significant limitation in pulmonary arterial hypertension (PAH). This intolerance greatly affects the quality of life and function of the individual with PAH, irrespective of its etiology. In PAH associated with connective tissue disorders (PAH-CTD), exercise intolerance is further amplified by the presence of coexisting musculoskeletal manifestations of CTD. The evaluation of exercise capacity and prescription for exercise training therefore becomes a challenge to the clinician. Areas covered: This review highlights factors contributing to exercise intolerance in PAH-CTD, evaluation methods of exercise capacity and an overview on exercise training and a roadmap for future research. Expert commentary: Exercise intolerance is a complex interplay of cardiovascular, pulmonary, and musculoskeletal systems. Data from cardiopulmonary exercise tests have shown predictive abilities for both diagnosis and prognosis. In its absence, the 6-min walk test can be used to provide similar information thereby making the role of exercise testing an invaluable evaluation method in PAH-CTD. Exercise training data in PAH-CTD are still sparse, though, data from PAH studies suggest potential benefit. However, more research is required in this area of testing and training for greater understanding on exercise hemodynamic, phenotypes, and training benefits.

Agreement of different reference equations to classify patients with COPD as having reduced or preserved 6MWD

BACKGROUND

Interpretation of the six-minute walk distance (6MWD) is enhanced by using recommended reference equations. Whenever possible, the choice of equation should be region-specific. A potential problem is that different equations for the 6MWD may have been developed for the same population, and it may be complicated to choose the most suitable.

OBJECTIVE

To verify the agreement of different reference equations in classifying patients with Chronic Obstructive Pulmonary Disease (COPD) as having reduced or preserved 6MWD.

METHODS

159 patients with COPD performed the six-minute walk test according to international standardization. They were classified as having reduced 6MWD if it was below the lower limit of normal. Five Brazilian equations (Iwama; Britto1; Britto2; Dourado; Soares) and the two non-Brazilian equations most cited worldwide (Troosters; Enright) were used. The agreement for patients classified as reduced or preserved 6MWD was verified by Cohen's Kappa (pair-to-pair) analysis. The proportion of patients classified as having reduced walked distance was compared by the Chi-squared test.

RESULTS

Agreement between equations varied largely in classifying subjects as having reduced or preserved 6MWD (Kappa: 0.10-0.82). Brazilian equations with the highest agreement were Iwama, Britto1 and Britto2 (Kappa>0.75). The proportion of patients classified as having reduced 6MWD was statistically similar only between equations in which the agreement was higher than 0.70.

CONCLUSION

Even reference equations from the same country vary considerably in the classification of reduced or preserved 6MWD, and it is recommended that the region-specific ones be used as they give with higher agreement for similar and comparable interpretation of the patients' functional exercise capacity.

An evaluation of activity tolerance, patient-reported outcomes and satisfaction with the effectiveness of pulmonary daoyin on patients with chronic obstructive pulmonary disease

BACKGROUND AND OBJECTIVE

Pulmonary Daoyin (PD) (evolved from ancient Chinese daoyin skills), is a rehabilitation technology that combines specially designed movements of the arms and body and controlled breathing exercises, to improve the physiological and psychological status of patients with chronic respiratory disease. Pulmonary rehabilitation is effective for patients with chronic obstructive pulmonary disease (COPD), and the efficacy of PD is unknown. The aim of this study is to investigate the effect of a PD program in enhancing activity tolerance, patient-reported outcomes and satisfaction with the effectiveness on patients with COPD.

MATERIALS AND METHODS

The multi-center, randomized controlled trial was conducted from November 2011 to June 2012 in local communities in cities of the 11 research centers in China. It included COPD patients (moderate to very severe) who were recruited from an outpatient clinic. A randomized controlled study included 464 COPD patients who were randomly allocated either to the PD group, participating in a 3-month, ten times-weekly supervised PD-based pulmonary rehabilitation program, or to a control group continuing with regular medical treatment alone. Data were gathered using the 6-minute walking distance (6MWD) test, COPD patient-reported outcomes (COPD-PRO) and Effectiveness Satisfaction Questionnaire for COPD (ESQ-COPD), which was filled out at baseline and 3 months post-intervention. SAS 9.2 was used for statistical analysis.

RESULTS

Of the 464 patients in the study, 461 were included in the full analysis set (FAS); 429 were in the per-protocol analysis set (PPS). After 3-month intervention, there was a significant difference between the two groups in 6MWD (FAS; P=0.049; PPS; P=0.041), total score and all domains of COPD-PRO (FAS; P=0.014; PPS; P=0.003) and ESQ-COPD (FAS; P=0.038; PPS; P<0.001).

CONCLUSIONS

The PD program was able to improve the activity tolerance level and satisfaction of COPD patients because of its effectiveness.

Predictive validity analysis of six reference equations for the 6-minute walk test in healthy Brazilian men: a cross-sectional study

BACKGROUND

The six-minute walk test (6MWT) is an important tool for evaluating functional capacity and exercise tolerance. The reference equations for the 6MWT in healthy subjects were established on the basis of American and European populations, but reference equations have been proposed with different variables for the Brazilian population.

OBJECTIVE

To analyze the predictive validity of six reference equations for the six-minute walking distance (6MWD) in healthy adult men.

METHODS

We evaluated 103 individuals in relation to level of physical activity (IPAQ), respiratory symptoms (MRC), handgrip strength, and 6MWD test. The data were submitted to a normality test, then the Bland-Altman agreement test was used to compare individual 6MWD values with that expected for each equation.

RESULTS

The subjects were active, with a mean age of 34.12 (SD=8.88) years and no respiratory symptoms. The mean of the 6MWD was 663.43 (SD=93.01)m. The 6MWD's predicted values came closest to the walked distance covered by Britto et al.'s equation (using BMI) of 647.62 (SD=38.62)m.

CONCLUSIONS

The equation proposed by Britto et al. using body mass index (BMI) was the closest to the 6MWD for the individuals studied and could be widely used as a reference tool during the 6MWT in healthy Brazilian men.

Does the incremental shuttle walk test require maximal effort in young obese women?

Obesity is a chronic disease with a multifaceted treatment approach that includes nutritional counseling, structured exercise training, and increased daily physical activity. Increased body mass elicits higher cardiovascular, ventilatory and metabolic demands to varying degrees during exercise. With functional capacity assessment, this variability can be evaluated so individualized guidance for exercise training and daily physical activity can be provided. The aim of the present study was to compare cardiovascular, ventilatory and metabolic responses obtained during a symptom-limited cardiopulmonary exercise test (CPX) on a treadmill to responses obtained by the incremental shuttle walk test (ISWT) in obese women and to propose a peak oxygen consumption (VO2) prediction equation through variables obtained during the ISWT. Forty obese women (BMI ≥30 kg/m2) performed one treadmill CPX and two ISWTs. Heart rate (HR), arterial blood pressure (ABP) and perceived exertion by the Borg scale were measured at rest, during each stage of the exercise protocol, and throughout the recovery period. The predicted maximal heart rate (HRmax) was calculated (210 - age in years) (16) and compared to the HR response during the CPX. Peak VO2 obtained during CPX correlated significantly (P<0.05) with ISWT peak VO2 (r=0.79) as well as ISWT distance (r=0.65). The predictive model for CPX peak VO2, using age and ISWT distance explained 67% of the variability. The current study indicates the ISWT may be used to predict aerobic capacity in obese women when CPX is not a viable option.

How to carry out a field walking test in chronic respiratory disease

EDUCATIONAL AIMS

To provide recommendations for conducting field walking tests in people with chronic respiratory disease, from the new European Respiratory Society/American Thoracic Society Technical StandardTo provide information to assist in selecting a field walking test in people with chronic respiratory disease.

KEY POINTS

The 6MWT, ISWT and ESWT are valid and reliable tests of functional exercise capacity in people with COPD. The 6MWT is also widely used in other chronic respiratory disorders.There is a learning effect for the 6MWT and ISWT, so two tests must be performed if the tests are being used to measure change over time, with the best distance recorded.The 6MWT is very sensitive to changes in the way it is conducted, including use of encouragement, provision of supplemental oxygen, changes in track layout and length, and use of wheeled walkers. These factors should be held constant when the test is repeated.The 6MWT, ISWT and ESWT are strenuous tests, with cardiorespiratory responses that are similar to those during a maximal incremental exercise test. As a result, the contraindications and precautions for these field walking tests should be the same as for a laboratory-based incremental exercise test.

SUMMARY

The European Respiratory Society (ERS) and American Thoracic Society (ATS) have recently published a Technical Standard which documents the standard operating procedures for the 6-min walk test (6MWT), incremental shuttle walk test (ISWT) and endurance shuttle walk test (ESWT). The Technical Standard shows that all three tests are valid and reliable measures of functional exercise capacity in people with chronic respiratory disease and makes recommendations for standardising their performance. Key findings and recommendations of the Technical Standard include: The 6MWT, ISWT and ESWT are strenuous tests which elicit cardiorespiratory responses that are similar to those observed during a maximal incremental exercise test. As a result, the contraindications and precautions for field walking tests should be consistent with those used for a laboratory-based incremental exercise test.There is strong evidence of a learning effect for the 6MWT and ISWT. Two tests should be performed when the 6MWT or ISWT are used to measure change over time.The 6MWT, ISWT and ESWT are responsive to treatment effects in people with chronic respiratory disease, particularly for rehabilitation.The 6MWT is very sensitive to variations in methodology, including use of encouragement, provision of supplemental oxygen, changes in track layout and length, and use of wheeled walkers. These factors should be documented and held constant on repeat testing.The lowest S pO2 recorded during a 6MWT is an important marker of disease severity and prognosis. Continuous pulse oximetry is recommended during the 6MWT, to ensure that the lowest S pO2 is recorded.In adults with chronic respiratory disease, a change in 6-min walk distance of 30 m or more indicates a clinically significant change has occurred.