|Year : 2021 | Volume
| Issue : 1 | Page : 22-28
Correlation of six minute walk test and incremental shuttle walk test with severity of airflow obstruction in patients with chronic obstructive pulmonary disease
Pavirala Sai Tej, Saka Vinod Kumar, G. Vishnukanth
Department of Pulmonary Medicine Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), India
|Date of Submission||02-Apr-2020|
|Date of Decision||15-Apr-2020|
|Date of Acceptance||20-May-2020|
|Date of Web Publication||15-Feb-2021|
Dr. G. Vishnukanth
Associate Professor, Department of Pulmonary Medicine Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Puducherry 605006
Source of Support: None, Conflict of Interest: None
Context: The field walking tests like 6MWT and ISWT are commonly used indicators of functional capacity in patients with cardiopulmonary diseases. This study was designed to assess the correlation of six minute walk distance (6MWD) and incremental shuttle walk distance (ISWD) with the severity of airflow obstruction (FEV1%) in patients with chronic obstructive pulmonary disease. Aims: Comparison of correlation of six minute walk test and Incremental shuttle walk test with the severity of airflow obstruction in COPD patients.Settings and Design: Hospital-based prospective cross-sectional study in a tertiary care centre. Methods and Material: One hundred and twelve (112) spirometrically confirmed COPD patients underwent 6MWT and ISWT. The diagnosis of COPD and its severity was assessed by the GOLD criteria. 6MWT and ISWT were done on the same patient with a gap of 5–6 hours and the distance walked (6MWD and ISWD) was correlated with the severity of COPD (FEV1). Statistical Analysis Used: One way ANOVA to compare mean distance walked in 6MWT and ISWT with different grades of COPD. Pearson Correlation was done to correlate packyears of smoking and age with 6MWD and ISWD. Results: The mean distance walked in the 6MWT and ISWT was estimated and compared across the four categories of GOLD grading. There was no statistically significant difference between the study subjects of corresponding GOLD grades based on the distance walked in 6MWT and in ISWT. However, a linear correlation was depicted between ISWD and post-bronchodilator FEV1. A model of linear regression showed that ISWD was an independent contributor to post-bronchodilator FEV1 in our study. Conclusions: Incremental shuttle walk test, an externally paced near to standard test with its incremental nature, can be used as an appropriate surrogate for FEV1 in determining the severity of airflow obstruction in COPD patients.
Keywords: COPD, correlation, field walking tests
|How to cite this article:|
Tej PS, Kumar SV, Vishnukanth G. Correlation of six minute walk test and incremental shuttle walk test with severity of airflow obstruction in patients with chronic obstructive pulmonary disease. J Assoc Chest Physicians 2021;9:22-8
|How to cite this URL:|
Tej PS, Kumar SV, Vishnukanth G. Correlation of six minute walk test and incremental shuttle walk test with severity of airflow obstruction in patients with chronic obstructive pulmonary disease. J Assoc Chest Physicians [serial online] 2021 [cited 2021 Jul 28];9:22-8. Available from: https://www.jacpjournal.org/text.asp?2021/9/1/22/309467
Key Messages: ISWT is a better field walking test than 6MWT in COPD patients
| Introduction|| |
Global initiative for Chronic Obstructive Lung Diseases (GOLD) defines Chronic Obstructive Pulmonary Disease (COPD) as a common, preventable and treatable disease that is characterized by persistent respiratory symptoms and airflow limitation that is due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles or gases.
The diagnosis of COPD requires a spirometry with a post-bronchodilator testing. It makes an objective measurement of airflow limitation. GOLD mentions a post-bronchodilator FEV1/FVC <0.70 to confirm the presence of persistent airflow limitation. However spirometry has its own limitations and airflow limitation in spirometry often does not reflect the patient’s symptoms. Persons report symptoms only when the lung function has worsened significantly. This will be even more in the people with sedentary life style. In this context, exercise testing helps in accurately assessing patients symptoms.
Functional capacity can be assessed by various walking tests. Six minute walk test (6MWT) is one of the objective tests which is simple, self-paced, well-tolerated, reproducible and is a good reflection of daily activities. Various studies prove that the reproducibility of 6MWT is more than the spirometric variables.,
The incremental shuttle walk test (ISWT) is another field walking test that is done to define the exercise capacity of COPD patients. In this test, the patient has to walk to and fro on a 10 m flat course, in which the pace of the subject is predetermined and is indicated by the bleeps via a pre-recorded audio tape. The physiological responses in ISWT closely match with that of the cardiopulmonary exercise testing (CPET) because of its incremental nature. The incremental shuttle walk distance (ISWD) is often considered as a prognostic factor in COPD patients to measure the cardiorespiratory fitness and is more reproducible than FEV1.
By comparing and correlating the above field walking test with the severity of airflow obstruction, we aimed to determine whether the self-paced 6MWT or the predetermined externally paced ISWT correlates better with the post-bronchodilator forced expiratory volume in the first second (FEV1) and can be used as a surrogate for determining severity of airflow obstruction in COPD patients.
- Comparison of correlation of six minute walk test and incremental shuttle walk test with the severity of airflow obstruction in COPD patients
- to determine whether 6MWT or ISWT correlates better with (FEV1) and can be used as a surrogate for determining severity of airflow obstruction in COPD patients.
| Methodology|| |
This study was a hospital-based cross-sectional analytical study done in the Department of Pulmonary Medicine, JIPMER from January 2017 to December 2018. It was a single arm study. All patients fulfilling the inclusion criteria were enrolled after taking informed written consent. Both the field walking tests were performed by the same patient with a gap of 5–6 hours. The demographic details, clinical findings were recorded in a predesigned proforma.
Sample size was estimated assuming alpha (α) 0.05, power (1−β)=0.80, correlation coefficient of 6MWT with severity of airflow obstruction in COPD patients =0.45. Expected correlation coefficient of shuttle walk test with severity of airflow obstruction in COPD = 0.70. Expected effect size was 0.3826, sample size was calculated to be 111 using G* power software version 3.0.10.
- Diagnosis of COPD (GOLD criteria 2015).
- Age over 18 years.
- Asthma and respiratory failure.
- Domiciliary oxygen therapy and noninvasive ventilation.
- Diseases (e.g. lung cancer, pulmonary tuberculosis, unstable angina, CHF, any other disease limiting patient’s movement).
- Acute exacerbation of COPD.
- Patients with active neurological, rheumatological or peripheral vascular diseases.
- Patients with elevated systolic blood pressure more than 180 mm Hg.
- Patients unable to perform spirometry/field walking tests (6MWT, ISWT).
- Patients not giving consent.
| Informed consent|| |
Written informed consent was obtained from all patients after explaining them the study in their local language.
| Randomization|| |
Simple randomization was done to assign the order of performing the tests in the study subjects. This randomization also ruled out the effect of one test over the other test. The subjects were allocated in such a way that they perform either of the tests first followed by the other test. For example, half of the patients performed the 6MWT first followed by ISWT and another half of the patients performed ISWT first followed by 6MWT.
| Brief procedure|| |
Three hundred and fifty (350) patients who were suspected to have COPD based on clinical history and physical findings were subjected to spirometry. Spirometry was done using Care Fusion Type Master ScreenTM PFT system which was available in the outpatient Department of Pulmonary Medicine, JIPMER hospital, according to the guidelines of the American Thoracic Society. Post-bronchodilator spirometry was done after nebulizing the patient with salbutamol solution 2.5ml (each ml containing Salbutamol equivalent to 5 mg) using an ultrasonic nebulizer. Diagnosis of COPD was according to GOLD criteria 2015.
All confirmed cases of COPD were admitted in hospital and these patients were subjected to 6MWT and ISWT to avoid/to attend any unavoidable events. In half of the patients, 6MWT was done first followed by ISWT and vice versa in the other half of the patients. The second test was performed only after vitals become stable or with a gap of 5–6hours
Six-Minute Walk Test
The six-minute walk test was conducted according to current ATS guidelines in a 30 m long internal corridor. This is a self-paced test aimed to walk as much as possible in six minutes. Participants were given instructions to walk back and forth along the corridor at their own pace. Each minute, participants were encouraged with the standardized statements. Patients were permitted to take rest while performing this test but were allowed to resume walking within that specified six minutes time as soon as they are able to do so.
Incremental Shuttle Walk Test
CD for performing ISWT was procured from Pulmonary Rehabilitation Department, University Hospitals of Leicester NHS Trust, Glenfield Hospital, Leicester. The basis for this incremental shuttle walk test is the protocol proposed by Singh et al. The basic idea of this ISWT is to walk, to and fro along the 10-meter course, keeping to the pace indicated by the bleeps on the prerecorded audiotape. Patients were instructed to walk at a steady speed to reach the cone at one end by the time they hear the first bleep, and the same to be repeated while they were hearing the subsequent bleeps. End of each shuttle was indicated by a single bleep and increase in speed was stipulated by triple bleeps. At first, their walking speed was very slow, but they are needed to speed up at the end of each minute. They had to stop walking only when they were unable to keep up with the determined speed or too dyspneic to do the test. The walking speed for the first minute was very slow. They have 20 seconds to complete each 10-metre shuttle. 12 stages were present and the walking speed was increased sequentially at 1 minute intervals.
At the end of each test, distance walked, oxygen saturation, systolic and diastolic blood pressure, heart rate, respiratory rate and perceived Borg’s scale were determined.
Categorical and ordinal variables were expressed as frequencies and percentages. The data for the continuous variables such as age, pulmonary function parameters, distance walked etc. were expressed as mean with S.D or median with range. Correlation analysis was used to identify the linear relations between distance walked and other parameters using Spearman’s rho or Pearson’s correlation. The comparison of continuous variables in relation to the severity of COPD was carried out using one-way analysis of variance or Kruskal-Wallis test. All statistical analyses were carried out at 5% level of significance and a P-value <0.05 was considered to be statistically significant.
Software used was SPSS version 19.0.
| Results|| |
Three hundred and fifty patients who had symptoms suggestive of COPD were screened. Out of the total 350 patients, 37 were unable to perform spirometry, 68 were diagnosed to have bronchial asthma, 55 had difficulty in walking, 31 were hypertensive (systolic Blood Pressure >180mmHg), 10 were presented with COPD exacerbations, 4 patients did not give consent and 33 were associated with other diseases (11-pulmonary tuberculosis, 8-lung cancer, 8-unstable angina, 6-heart failure) and 112 patients who satisfied the inclusion and exclusion criteria were considered for the study.
The mean age of the study subjects was 58.07 ± 9.53 years and more than 80% of the study subjects were in the age group of 51–70 years [Table 1]. Males formed a major part of the study population (94.6%, n = 106). Of the 112 study subjects, 91 (81.25%) were smokers. All of the smokers were males.
All the study subjects were diagnosed as COPD after performing spirometry. Based on post-bronchodilator FEV1, the study subjects were categorised into four grades according to the GOLD criteria 2015. All the study subjects were subjected to perform 6MWT and ISWT. The distance covered by the study subjects in the field walking tests (6MWT and ISWT) were measured as six minute walk distance (6MWD) and incremental shuttle walk distance (ISWD) respectively.
The mean distance walked in 6MWT was correlated with post-bronchodilator FEV1(%). Though there was a reduction in the distance walked with increase in the grade of FEV1, the association was not statistically significant [Table 2]. The mean distance walked in the 6MWT was estimated and compared across the four categories of GOLD grading [Table 3]. Test statistics of one way ANOVA was done. It was found that F=0.679 with a P > 0.05. This indicates that there was no statistically significant difference between the study subjects of corresponding GOLD grades based on the distance walked in 6MWT. Also we observed that there is no linear increase or decrease in the mean distance walked in 6MWT in various grades of COPD. We attempted to look for the effect of age and pack years of smoking in relation to the 6MWD. A significant negative correlation was observed between 6MWD and age implying that as the age increases, there was a linear decrease in the 6MWD [Table 4].
|Table 2 Correlation of 6MWD and ISWD in relation to post-bronchodilator FEV1 n = 112|
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|Table 3 Observations of 6MWD and ISWD performed by study subjects in different GOLD grades (N = 112)|
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|Table 4 Correlation of 6MWD and ISWD in relation to age and smoking in pack-years (N = 112)|
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Observations of ISWD with other parameters
The correlation of ISWD with post-bronchodilator FEV1 was done [Table 2]. There was a statistically significant correlation between ISWD and post-bronchodilator FEV1 (P = 0.012) when observed in all subjects without grading them based on the severity of COPD.
A linear correlation was depicted between ISWD and post-bronchodilator FEV1. A model of linear regression showed that ISWD was an independent contributor to post-bronchodilator FEV1 in our study. The derived reference equation was: post-bronchodilator FEV1(pred) = 38.14+0.030 (ISWD in meters).
The mean distance walked in the ISWT was estimated and compared across the four GOLD grades [Table 3]. Test statistics of one way ANOVA was done to compare the mean distance walked across the four grades in GOLD staging. It was found that F=2.664 with a P > 0.05. This indicates that there was no statistically significant difference between the GOLD grades based on the distance walked in ISWT. However, in contrast to 6MWT, we observed a linear decrease in the distance walked in ISWT in different grades of COPD [Figure 1] indicating a clinically significant difference in ISWD in different GOLD stages.
The observations of ISWD in relation to age and smoking in terms of pack-years is shown in [Table 4]. Similar to 6MWD, a significant negative correlation was found between age and the distance walked in incremental shuttle walk test (r = −0.318, P = 0.001). The correlation of pack years with ISWD showed a significant negative correlation (r = −0.253, P = 0.007). This indicates that as the age or the number of pack-years smoked increase, there was a linear decrease in the distance walked in ISWT. The same is depicted in a scatter diagram [Figure 2].
Oxygen saturation, heart rate, respiratory rate, and dyspnoea Borg scale were evaluated before and after the field walking tests. Pre-test and post-test comparison of these parameters are shown in [Table 5]. There was no significant difference in the pre-test parameters between the two exercise tests (P > 0.05). However we observed that there was a significant decrease in oxygen saturation at the end of both the tests. This decrease in the post-test oxygen saturation was statistically significant in the ISWT than in 6MWT. There was also a statistically significant elevation of post-test parameters like post-test heart rate, respiratory rate and dyspnoea Borg score on comparison with the pre-test values. This increase in post-test parameters as compared to pre-test parameters was noted in 6MWT and ISWT tests. This increase was higher with ISWT than 6MWT.
|Table 5 Cardiorespiratory parameters in 6MWT and ISWT among the study subjects (N = 112)|
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| Discussion|| |
We compared 6MWD as assessed by 6MWT with severity of airflow obstruction (post-bronchodilator FEV1) as assessed by spirometry. There was no statistically significant correlation observed. Our findings are similar to studies by Gosselin key et al., Hodgev et al., Chuang et al. and Behnke et al.,,, In all these studies it was observed that there was no significant correlation between post-bronchodilator FEV1 and 6MWD. We believe that in 6MWT, patients walk at their own pace and are allowed to stop if they feel breathless. Thus patients may not reach their maximal level of exercise tolerance and perform the test at their comfort. This might be a reason that 6MWD is not correlating with FEV1. On the contrary, studies by Maji et al., Santos et al., Peruzza et al. and Wijkstra et al. found positive correlation between 6MWD and FEV1.,,,
We made an attempt to correlate incremental shuttle walk distance(ISWD) with severity of airflow obstruction and observed a statistically significant correlation between the two. Similar results have been observed by Singh et al., Dyer et al. and Ushiki et al.,, In order to predict lung function from field walking tests, the tests should give a proper lung assessment like the standard cardiopulmonary exercise test (CPET). ISWT being an externally paced, near to standard CPET simulates a familiar day to day activities in which symptoms are more easily identified because of its incremental character. Thus the severity of airflow obstruction and incremental shuttle walk distance have a positive correlation. On the contrary, Emtner et al. did a study in 21 COPD patients to find out if ISWD can be used as an independent marker for exacerbations and hospitalisation. They had shown that the correlation between ISWD and post-bronchodilator FEV1 was not statistically significant.
The correlation between age and the distance walked in 6MWT showed a significant negative correlation implying that the distance walked decreased with an increase in age. This is in concurrence with study by Iwama et al. in Brazil. The correlation between age and the distance walked in ISWT was also done and a significant negative correlation was found. This indicates that the distance walked decreased with the increase in age. Agarwal et al. tried establishing normal reference values in ISWT for healthy indian individuals and observed that with an increase in the age there was a decrease in distance walked in ISWT. However we observed that the correlation between age and 6MWT was not statistically significant. This implies that ISWT is a better predictor of exercise tolerance with respect to age groups.
We observed that there was a decrease in oxygen saturation at the end of both the tests. Further the oxygen saturation in ISWT at the end of the test was found to be significantly lower than that of the 6MWT. A lesser decrease in oxygen saturation in 6MWT in our patients can be because, a few of them who perceived more breathlessness tend to walk less distance and stopped without a significant decrease in oxygen saturation. A greater decrease in ISWT may be because of its predetermined pace and incremental character. It is worth mentioning that Seixas et al. reported that the oxygen saturation observed at the end of the incremental shuttle test was decreased even in healthy individuals. We also had a slightly different observation. Few patients in 6MWT and ISWT had an increased end of the test oxygen saturation when compared to pretest oxygen saturation.Heart rate is an important parameter to assess the immediate physiological response of the cardiopulmonary systems. Heart rate measured at the end of exercise tests in all the study subjects was more than the baseline heart rate. This finding was similar in both the field walking tests, but this increase in heart rate was more in ISWT than in 6MWT [Table 5]. This finding is similar to a study by Hill et al. in which they compared various cardiorespiratory responses in 24 COPD patients.
In our study, post test dyspnoea score measured using Borg scale was more in ISWT than in 6MWT. This is similar to Hodgev et al. who compared the cardiovascular and dyspnoea responses between ISWT and 6MWT in 20 COPD patients. They found that ISWT showed responses greater than 6MWT. Our study also showed higher post-test heart rate and dyspnoea Borg score in ISWT than 6MWT. This may be because in 6MWT study subjects were not reaching their maximal effort as it was limited to time and the patient can walk with their own speed. This makes the 6MWT, a submaximal exercise test and uses aerobic metabolism as the main source of energy. In contrast, ISWT requires anaerobic metabolism along with aerobic mechanism as ISWT is an externally paced test with predetermined speed involving a range of exercises from slow walking to running, making the patients to reach their maximal effort in an incremental manner.
| Limitations|| |
The study population included only stable COPD patients, hence the effect on exacerbations of COPD cannot be assessed. Also the study subjects were predominantly males and smokers, hence extrapolation of the study observations to non-smokers and females may not be accurate. Majority of our study population was not affordable for standard treatment of COPD (long-acting muscarinic antagonist or long-acting beta agonists) and hence effect of treatment on the exercise tests could not be done.
| Conclusion|| |
6MWD which was a primary outcome in 6MWT showed statistically nonsignificant correlation with severity of airflow obstruction (FEV1). ISWD determined as a primary outcome of the ISWT demonstrated a significant positive correlation with severity of airflow obstruction (FEV1).
Incremental shuttle walk test, an externally paced near to standard test with its incremental nature can be used as an appropriate surrogate for FEV1 in determining the severity of airflow obstruction in COPD patients. Further long term and multi-centric studies should be conducted to confirm the benefits and to elucidate its usage in determining the severity of COPD.
The authors would like to acknowledge the help rendered by Dr. Dharm Prakash Dwivedi, Associate Professor and Dr. V. Palanisamy Junior resident of pulmonary medicine, JIPMER in helping with the research and preparation of manuscript.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]