|Year : 2015 | Volume
| Issue : 1 | Page : 9-13
Correlation of six minute walk test with spirometric indices in chronic obstructive pulmonary disease patients: A tertiary care hospital experience
Abhijit Kundu1, Arnab Maji1, Supriyo Sarkar2, Kaushik Saha3, Debraj Jash4, Malay Maikap1
1 West Bengal, India
2 Department of Pulmonary Medicine, Malda Medical College and Hospital, Malda, West Bengal, India
3 Department of Pulmonary Medicine, Burdwan Medical College and Hospital, Burdwan, West Bengal, India
4 Department of Pulmonary Medicine, Nil Ratan Sircar Medical College and Hospital, Kolkata, West Bengal, India
|Date of Web Publication||12-Dec-2014|
2 No Ichlabad, Barabenepara, Sripally, Burdwan - 713 103, West Bengal
Source of Support: None, Conflict of Interest: None
Background: Six-minute walk test (6MWT) is a simple, objective, reproducible test which correlated well with different spirometric indices, and thus able to predict severity of chronic obstructive pulmonary disease (COPD) and can replace spirometry in resource poor set-up. Aims and Objectives: To find out correlation between spirometric indices (forced expiratory volume in 1 s (FEV 1 ), forced vital capacity (FVC), and peak expiratory flow rate (PEFR)) and 6-minute walk distance (6MWD) in COPD patients, and thus to assess whether 6MWT can replace spirometry. Settings and Design: Institution based cross-sectional observational study. Materials and Methods: Eighty patients of COPD (diagnosis confirmed by Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2010 criteria) were enrolled for the study after applying exclusion criteria. All patients underwent spirometric measurement of FEV 1 , FVC, PEFR, and ratio of FEV 1 and FVC and test repeated after bronchodilation by 200-400 μg of salbutamol. 6MWT was performed following American Thoracic Society (ATS) protocol of 6MWT and distance was measured in meters. Results: We found significant linear correlation of 6MWT with post-FEV 1 (r = 0.478, P < 0.001), post-FVC (r = 0.454, P < 0.001), and post-PEFR (r = 0.408, P < 0.001), but no correlation with FEV 1 /FVC (r = 0.250, P = 0.025). We also found significant correlation of 6MWT with BODE (body mass index (BMI), airway obstruction, dyspnea, and exercise capacity) index (r = −0.419, P < 0.001). Conclusions: 6MWT can be a useful replacement of spirometry in assessment of severity of COPD.
Keywords: Chronic obstructive pulmonary disease, correlation, six-minute walk test, spirometric indices, severity
|How to cite this article:|
Kundu A, Maji A, Sarkar S, Saha K, Jash D, Maikap M. Correlation of six minute walk test with spirometric indices in chronic obstructive pulmonary disease patients: A tertiary care hospital experience. J Assoc Chest Physicians 2015;3:9-13
|How to cite this URL:|
Kundu A, Maji A, Sarkar S, Saha K, Jash D, Maikap M. Correlation of six minute walk test with spirometric indices in chronic obstructive pulmonary disease patients: A tertiary care hospital experience. J Assoc Chest Physicians [serial online] 2015 [cited 2019 Jan 18];3:9-13. Available from: http://www.jacpjournal.org/text.asp?2015/3/1/9/146843
| Introduction|| |
Spirometric measurement of post-bronchodilator forced expiratory volume in 1 s (FEV 1 ) is essential for establishing the diagnosis, assessment of severity (staging), to predict the outcome, and to plan treatment in chronic obstructive pulmonary diseases (COPDs). Measurement of the walking distance is used to assess functional capacity of patients of COPD. Six-minute walk test (6MWT) is a simple, objective, and reproducible test. In 2002, the American Thoracic Society (ATS) approved the 6MWT as a standard test for clinical pulmonary function laboratories. The relationship between the walking distance in a certain period of time and the functional capacity of patients in COPD has been investigated in several studies. ,, Moreover, measurement of 6MWT is more reproducible than measurement of FEV 1 . , The facility of spirometry is not available in many rural areas of India because of lack of infrastructure where 6MWT can be done easily. Therefore in this study, we aimed to correlate 6-minute walk distance (6MWD) with different spirometric indices, and thus to evaluate whether 6MWT can replace spirometry in predicting severity of COPD.
| Materials And Methods|| |
Our study was ethically cleared by the Ethical Committee formed in our institution. This cross-sectional observational study was conducted in our medical college in the study period extending from 1 st April 2011 to 31 st March 2012. We included 80 patients with stable COPD attending the outpatient department in the stipulated study period and diagnosis of COPD was established by clinical symptoms and spirometric data of ratio of FEV 1 and forced vital capacity (FVC) ≤ 0.7.  We excluded patients who had clinical or radiological evidence of pneumonia, blood pressure ≥ 180/100mmHg, and resting heart rate > 120/min prior to 6MWT, evidence of left ventricular failure (LVF), ischemic heart disease (IHD), or any major cardiac disease, neuromuscular disease of the lower extremities, peripheral vascular disease, and those who refused to give informed written consent for the study. Pulmonary function tests were conducted as per ATS recommendation using computerized flow sensing spirometer with RMS Helios 3.0 software. Patient was given proper instruction during the test and the test was repeated 15 minutes after the administration of a short acting beta agonist (200-400 μg of salbutamol). Exhalation time was at least 6 s and end of test was indicated by a 2 s volume plateau. Spirometric indices including FEV 1 , FVC, and peak expiratory flow rate (PEFR) were tested. At least three forced expiratory maneuvers that satisfied ATS criteria were done for each patient of which the test with highest values were accepted. 6MWT was performed in a 30-m long and ventilated indoor corridor according to ATS guidelines.  All the patients underwent the 6MWTwithin1 h of spirometry. Each patient rested for atleast 10 min prior to the 6MWT. At the start of the test, the patients' heart rate, blood pressure, and oxygen saturation were measured. Patients were given proper instructions. Encouraging phrases such as "keep up the good work", "well done", and "good" were used during the test. All the subjects were allowed to stop after appearance of chest pain, dyspnea, or diaphoresis during the test and then continue walking when they felt better. However, the resting time was included in the 6-minute time period. The test was discontinued if patients experienced any chest pain, severe dyspnea, spasm of lower extremity muscles, or if the patient wanted to quit. At the end of the test, blood pressure, heart rate, oxygen saturation by pulse oximeter, and the distance walked for 6 minutes were recorded in meters. We calculated BODE index consisting of body mass index (BMI), airflow obstruction, dyspnea, and exercise capacity for each patient.  The patients were observed for 10-15 minutes after the test to assess any possible untoward effects. Statistical analysis was done by applying analysis of variance (ANOVA) f-test, and estimating P value, correlation coefficient (r), and regression analysis by Microsoft Excel Software2011 version.
| Results|| |
Our study included 80 patients of stable COPD. Patients were classified into five age groups: 40-44, 45-49, 50-54, 55-59, and more than 60 years of age [Table 1]. The number of male and female patients were 71 (88.75%) and nine (11.25%), respectively. Sixty-seven patients (83.75%) were in the 55 years or above age group. Statistical analysis of all the parameters (age, weight, height, BMI, spirometry indices, BODE index, pulse rate, and oxygen saturation before and after the tests and 6MWD) which we noted during the study is summarized in [Table 2]. Severity of the disease was classified according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) staging [Table 3]. Among the study population 41 patients (51.25%) were in stage II, 35 patients (43.75%) were in stage III, and four patients (5%) were in stage IV disease. None of our patients was in GOLD I stage. Ninety-five percent of our patients (n = 76) belong to stages II and III.
We calculated the mean and standard deviation of 6MWD values among different GOLD staging of COPD patients. The mean value of 6MWD was 334.63 m with standard deviation (SD) of 31.65 in patients with stage II COPD. Whereas, the means and SDs of 6MWD were 305.42 ± 32.79 and 281.25 ± 44.04 among stage III and stage IV COPD, respectively [Table 4].
|Table 4: Mean and standard deviation of 6MWD values among different GOLD staging|
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We correlated post-bronchodilator FEV 1 data (in liter) with 6MWD (in meter) [Figure 1]. We found correlation coefficient (r) was 0.478 with a P < 0.001; which means that there was as positive correlation between the above variables and the factor is 0.478 (correlation ranges between +1 and −1) [Table 5]. We estimated the analysis of variance (ANOVA) results for the two variables and found the F = 23.097 with a P < 0.001. So there was a significant functional relationship between the FEV 1 and 6MWD. We also performed regression analysis of the study data. The regression equation was y = 0.0056x − 0.5099 with a P < 0.001; Where x = 6MWD and y = post-FEV 1 . The finding implied that there was a linear relationship between 6MWD and post-FEV 1 .
|Figure 1: Scatter diagram of 6-minute walk distance with post-FEV1 FEV1 = forced expiratory volume in 1 s|
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We correlated post-bronchodilator PEFR data (in liter) with 6MWD (in meter) [Figure 2] and [Table 5]. We found correlation coefficient (r) was 0.408 with a P < 0.001; which means that there was a positive correlation between the above variables and the factor is 0.408 (correlation ranges between +1 and −1). We estimated the ANOVA results for the PEFR data (in liter) with 6MWD (in meter) and found F = 15.622with a P < 0.001. So there is a significant functional relationship between the PEFR and 6MWD. We also performed regression analysis of the study data. The regression equation was y = 0.0133x − 1.0096 with a P < 0.001; where x = 6MWD (meter) and y = post-PEFR (liter). The finding implied that there was a linear relationship between 6MWD and post-PEFR.
|Figure 2: Scatter diagram of 6-minute walk distance with post-PEFR PEFR = Peak expiratory flow rate|
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We correlated post-bronchodilator FVC data (in liter) with 6MWD (in meter) [Figure 3] and [Table 5]. We found correlation coefficient (r) was 0.454 with a P < 0.001; which means that there was as positive correlation between the above variables and the factor is 0.454 (correlation ranges between +1 and −1). We estimated the ANOVA results for the FVC data (in liter) with 6MWD (in meter) and found F = 20.289with a P < 0.001. So there was a significant functional relationship between the FVC and 6MWD. We also performed regression analysis of the study data. The regression equation was y = 0.0065x - 0.0527 with a P < 0.001; where x = 6MWD (meter) and y = post-bronchodilator FVC (liter). The finding implied that there was a linear relation between 6MWD and post-bronchodilator FVC. We did not find any significant correlation between 6MWD with ratio of post-bronchodilator FEV 1 and post-bronchodilator FVC (post-FEV 1 /FVC).
|Figure 3: Scatter diagram of 6-minute walk distance with post-FVC FVC = Forced vital capacity|
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We found a significant negative correlation (Pearson correlation coefficient r = −0.419, P < 0.001) between 6MWD and BODE index in study population, but we didnot find any significant correlation between 6MWD with BMI [Table 5].
| Discussion|| |
COPD is a leading cause of morbidity and mortality worldwide and it has a definite social and economic impact. World Health Organization (WHO) predicted that COPD will be the third leading cause of mortality and fifth leading cause of morbidity in 2020.  So assessing the disease severity and treating it appropriately is of utmost importance. GOLD advocated spirometric measurement of post-bronchodilator FEV 1 for assessing the severity of COPD and thereby staging the disease and treatment as per staging. Spirometric test is costly and is not available in many resource-poor ends of India. Many studies conducted worldwide showed definite correlation between 6MWT with different spirometric indices.
The 6MWT is a practical, simple, and easy to perform tool that provides a global assessment of functional capacity in patient with COPD. It is also used for pre- and postoperative evaluations in lung transplantation and lung volume reduction surgery.  In addition, 6MWT is used to monitor the response to therapy and to predict the mortality and morbidity of patients with chronic respiratory disease like idiopathic pulmonary fibrosis, pulmonary artery, hypertension, and COPD.  In 1963, Balke first introduced a simple method to look at the functional capacity of patients with COPD through measuring the total distance they could walk during a certain period of time.  Then in 1986, a 12-minute walk test (12MWT) was used by Cooper to assess the physical fitness of healthy individuals.  Next improvisation came through Butland et al., who showed that there was no significant difference between the12 MWT and their 6MWT in predicting the functional capacity of COPD patients.  In 2002, the ATS approved the 6MWT as a standard test for clinical pulmonary function laboratories. Our study showed a positive linear correlation of 6MWT with absolute values of FEV 1 , FVC, and PEFR, thus 6MWT predicted severity of COPD in individual patient. In 2007 a longitudinal study was done using 6MWD as long-term follow-up in COPD patients by Casanova et al., who showed that 6MWD declined by 19% (16 ml/year) over the 5 years (P = 0.001) compared with baseline in patients with ATS/European Respiratory Society stage III COPD (FEV 1 30-50% predicted) and by 26% (15 ml/year) in patients with stage IV COPD (FEV 1 < 30% predicted).  Other recent studies by Roozbeh et al., Mehta and Kumari, and Carter et al., determined the association between 6MWT and expiratory volumes in COPD patients and their results are compatible with the results of our study. ,, We also reproduced the result published by Knox et al., proving the relationship between the PEFR value and the 6MWD. 
Our study showed the lack of association between the 6MWD and FEV 1 /FVC ratio previously reported by other researchers and contradicted the data published by Chlumsky et al. ,,
The BODE index was opted for its use to determine prognosis in COPD patients. The BODE index includes four variables (BMI, airway obstruction, dyspnea, and exercise capacity) that characterize the major alterations found in such patients. The BODE index contains a component each that quantifies obstructive disorder by FEV 1 and that detects the perception of dyspnea. In addition there are two independent components which reflect the systemic consequences of COPD, and they are the distance covered on the 6MWT and the BMI. We found a significant negative correlation of 6MWT with BODE index in our study which implies that with increasing BODE index (i.e. with increasing severity of disease) there was decease in 6MWD. There in this way 6MWT also was able to predict severity of COPD. Though BMI correlates well with severity of COPD as shown by Landbo et al., in their study, we did not find a strong correlation between BMI and 6MWD and this finding was comparable with the study done by Santana et al. ,
In this study we demonstrated that 6MWT significantly correlated with absolute values of FVC, FEV 1 , PEFR, and also with the BODE index. Thus, we conclude that 6MWT can replace spirometry in assessment of severity of COPD. But there are few limitations in our study such as no healthy person was taken as control and we could not compare 6MWD of study population with healthy control, post-bronchodilator 6MWT was not done in our study, but a previous study suggested that using inhaled bronchodilators prior to the 6MWTmightimprovethe results, episodes of COPD exacerbations were not considered during study as it may have effect on 6MWT. 
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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