| Abstract|| |
BACKGROUND: Six minutes walk test (6MWT), is a sub-maximal exercise test, used as a clinical indicator of the functional capacity, in patients with cardiopulmonary diseases. Its safety, validity, reliability and its correlation with several physiological instruments, are well studied. However, there are no published data on 6MWT, in the Saudi population. We are reviewing our experience with 6MWT and assessing its safety and its correlation with pulmonary function variables, in patients with pulmonary diseases, in our local population.
MATERIALS AND METHODS: We consecutively studied patients with pulmonary diseases, who underwent 6MWT and pulmonary function test in King Khalid University Hospital, from June 2003 to December 2004. The 6MWTs were conducted according to the American Thoracic Society guidelines. Spirometry, lung volumes and diffusion capacity measurements were correlated with the absolute walked distance.
RESULTS: One hundred and twenty nine tests were performed. All patients were of the Saudi community (59% female), with mean age of 43±15 years. Out of 129 patients, 65 patients had proven respiratory diagnosis. In all patients, the test were performed with no serious complications. The six minute walk distance (6MWD) had correlation with patient's height (r=+0.40, P <0.001), but not with patients' weight, BMI, borg scale, or oxygen saturation. The 6MWD correlated significantly with Dlco (r=+0.52, P <0.01), FVC (r=+0.46, r<0.001) and had a weaker relation with FEV1 (r=+0.31, P <0.05). The test had no significant correlation with lung volumetric parameters (TLC, FRC and RV).
CONCLUSION: 6MWT is simple and safe test in evaluating patients with chronic pulmonary diseases in the Saudi population. In our study, 6MWD showed correlation with spirometric parameters and diffusion capacity. Further studies are needed to evaluate 6MWT in a more homogenous patients' population.
Keywords: Six minute walk test, pulmonary function test.
|How to cite this article:|
Al Ameri HF. Six minute walk test in respiratory diseases: A university hospital experience. Ann Thorac Med 2006;1:16-9
The six-minute walk test is an objective method, to measure the ability to perform daily living activities. It is more often performed, to evaluate the functional status, monitor therapy, or assess the prognosis in patients with cardiac and pulmonary diseases. In comparison to traditional pulmonary exercise test, 6MWT needs less technical support or equipment, making it a simple and inexpensive method to measure functional capacity. The validity and the reliability of 6MWT was studied in different conditions, including obstructive lung diseases, interstitial lung diseases, pulmonary hypertension, heart failure and peripheral arterial diseases. ,,,,,,,,
The safety of 6MWT was explored in several populations. A study of 6MWT in elderly individuals and in patients with ischemic heart disease found the test to be safe, reliable and correlates with several other parameters.,, Correlation of 6MWD and pulmonary function test measurements were seen in patients with chronic respiratory diseases. In a study by Wijkstra and coworkers, 6MWD correlated well with FEV1 and FVC in 40 patients with COPD. A similar correlation was also observed with Dlco, in patients with interstitial lung diseases. To our knowledge, there are no published data of 6MWT done in the Saudi population. The safety profiles and the correlation of 6MWT with pulmonary function measurements in respiratory diseases, were not addressed in the Saudi subjects.
The primary objective of this study is to evaluate the safety of conducting 6MWT, in our local population. The secondary objective includes the evaluation of the walked distance in relation to spirometric, volumetric and diffusion capacity measurements of lung function, in patients with respiratory diseases.
| Materials and Methods|| |
The study was conducted in KKUH, a tertiary regional hospital, from June 2003 to Dec 2004, in consecutive patients with pulmonary diseases, referred for 6MWT from the inpatient ward, or outpatients clinics. Patients were included from the age of 12 to 70 years old, they were in stable clinical conditions and they were not on oxygen therapy. Patients were excluded if they were unable to perform the test, because of active neurological, rheumatological, or peripheral vascular diseases. Patients with elevated systolic blood pressure more than 180 mmHg, resting tachycardia more than 120 beat per minute, or with current chest pain, were considered to be unsafe to perform the test and they were excluded. The demographic features of patients (age, sex, weight, height and BMI) were recoded prior to 6MWT. There were a subgroup of patients referred by consultant pulmonology physicians, with a definite respiratory diagnosis and they were included for further pulmonary function testing.
Six minute walk test
At the time of the test, the patient's heart rate, blood pressure and oxygen saturation, were measured. The patient was asked to indicate his or her level of "effort to breath", by using a Borg scale, a 12 points scale from 0 to 10, with corresponding expression figures in escalating intensity, printed on easy readable card, where 0 is "nothing at all" and 10 is "very, very severe". The 6MWT was performed according to the ATS guidelines and it was supervised by a trained respiratory technician throughout the test. Subjects were asked to walk at their own pace, along a 30 m long and straight hospital hallway marked at one meter intervals. Each patient was instructed to walk as much distance as possible, in 6 minutes. No encouragement was offered, but the patient was told standardized phrases, to indicate the time remaining. The patient was allowed to stop, if symptoms of significant distress occurred, like severe dyspnea, chest pain, dizziness, diaphoresis, or leg cramps. However, the patient was asked to resume walking as soon as possible, if he or she could. At the end of six minutes, the patient was asked to stop and a repeated measurement of blood pressure, heart rate, oxygen saturation by pulse oximeter and Borg score, were measured and the distance walked for 6 minutes was recorded. The patients were asked to be observed for a 10-15 minutes period after the test, to assess any possible complications. Patients who started to walk but did not complete the test, were included in the study.
Pulmonary function test
Patients with definite respiratory diagnosis underwent a pulmonary function test, using standardized protocol by ATS recommendation. Spirometric indices including FEV 1 , FVC and peak expiratory flow, were tested using computerized spirometer. Total lung capacity, RV and ERV, were calculated from the measurement of thoracic gas volume, using whole body plathysmograph (Jeager, Master Screen PFT, Germany). The diffusion capacity of carbon monoxide was measured by single breath hold technique and the result was corrected according the patient's level of hemoglobin. Reproducibility was ensured by doing at least three measurements for each lung function and the predicted values were calculated.
The results are reported as mean ± standard deviation. The absolute (6MWD) in meters was used, instead of the predicted value that was previously reported. The safety profile was assessed in all patients by calculating the number of cardiac and hemodynamic events in the studied population, that required to be managed acutely by a physician. The correlation between 6MWD and the patients' demographic features and pulmonary function test measurements, were evaluated using Pearson's coefficient. The criteria for statistical significance was set to be P <0.05. Analysis was carried out using the Sigmastat computer program for Windows (edition 3.1).
| Result|| |
Patient characteristic and safety
From the 132 patients who were referred for 6MWT, three patients were excluded (two had elevated systolic blood pressure and one patient had resting tachycardia). From the 129 patients tested, ninety two patients were referred from outpatients' clinic with stable conditions and 37 patients with no active respiratory diseases were referred from inpatients wards. All patients were Saudis, with a mean age of 43.1±15.4 years. There were 76 women and 53 men, in the studied population.
There were no complicated events or hemodynamic changes associated with or after the test performance, that required emergency management. Four patients (partial completers) did not complete the test because of leg cramp and dyspnea. One patient had elevated blood pressure of 172/93 mmHg at base line and he had increased blood pressure measurement to 213/113 at the end of exercise, with no concurrent symptoms.
Correlation of 6MWD and pulmonary physiological indices
Of the 129 patients tested, 65 patients were diagnosed by their referring physicians with interstitial lung diseases (62%), small airway diseases (37%) or pulmonary vascular diseases (1%). The demographic features are summarized in [Table - 1]. There was no significant difference in age between male and female patients. Men tend to be significantly taller and with BMI less than women. Overall, the average 6MWD was 341±70 m, for the whole group. The mean distance walked for men was 390 ± 75 m, which it was significantly ( P <0.001) more than distance walked by women (mean=305 ± 57m). There was no correlation between the walked distance in 6 minutes and the patient's age, weight, or BMI. However, there was a significant correlation between the distance and the patients' height (r= +0.4, P <0.001).
The 6MWD had no significant correlation with the level of borg-scale or oxygen saturation at baseline, or at the end of the test. The patients' pulmonary function test measurements are summarized in [Table - 2]. There were no significant differences in FEV 1 , FVC, TLC, or Dlco, between female and male patients. Spirometric values correlate modestly with 6MWD. FVC had a stronger positive correlation with distance walk than FEV1 (r=+0.46, P <0.001 and r=+0.31, P <0.05 respectively). The 6MWD had no significant correlation with volumetric lung measurements, including TLC, ITGV and RV. There was a significant correlation between 6MWD and Dlco, in patients with respiratory diseases (r=+0.52, P <0.01). The correlations between 6MWD and different physiological indices are summarized in [Table - 3].
| Discussion|| |
The ability to walk for a distance, is an easy way to measure exercise capacity in patients with cardiac and pulmonary diseases., A variety of walk tests, including self-paced walk tests, controlled-pacing incremental walk tests and time- paced tests, are considered to be objective measurements of functional capacity. Six minute walk test is found to be an effective way of assessing exercise tolerance. Its validity, reliability and reproducibility, were studied in several populations.,,,,, This the first study that looked at 6MWT in the Saudi population. We showed that 6MWT can be safely performed with no untoward events or complications, that required emergency management. It was highly tolerable in different age groups, gender and in patients with different respiratory conditions. Only 3% of patients were not able to complete the tests because of leg pain, fatigue, or dyspnea. Because of the small number of patients who partially completed the test, we could not assess the characteristic demographic or physiological feature of this group, in comparison to patients who were able to complete the 6MWT.
The distance walked by male patients in our studied population was significantly more than the distance covered by female patients. Such difference has been reported in several other studies of healthy adults. A reference equation published by Enright et al found that gender, height and weight, were independent factors associated with 6MWD. In our studied population, the walked distance had a significant correlation with the subjects' height, but not with age, weight, or BMI. The studied population included patients with different respiratory conditions. Most of the studies that showed relation of 6MWD and patient's demographic characteristics, were in healthy individuals, which could explain the lack of correlation in our study.
In this study, we demonstrated that distance walked in six minutes significantly decreased in proportion, with decrease in FEV 1 and FVC. Six minute walk distance has been shown to be a useful marker for the severity and progression of obstructive lung diseases.,,,,, Wijkstra and his group showed significant correlation between spirometric measurement and six minute walk distance, in patients with sever COPD. A similar correlation was found between FEV 1 and FVC and walk distance, in patients with severe bronchial asthma.
The positive relation of 6MWD and Dlco, was seen in patients with interstitial lung diseases (ILD) and obstructive lung diseases., In present study, Dlco was the most significant parameter in relation to the walked distance. This relation was more significant in a subgroup of patients with ILD, than with other conditions. On the other hand, there was no correlation between TLC, ITGV and RV with 6MWD, in our studied population. There are only few studies, which showed the significance relation of TLC with 6MWD. Such correlation was more apparent in patients with idiopathic pulmonary fibrosis and it was not studied in patients with other interstitial or obstructive lung diseases.
The correlation of 6MWT and pulmonary function test, in patients with respiratory diseases, makes this test easy and a simple tool for assessing the disease status. From our observation, such tests have been underutilized in our local clinical and research institutes, especially in patients with severe respiratory disability, in whom the lung function test may be an insensitive tool for measuring functional status. This study also confirmed that the 6MWT can be safely performed even in patients with advanced respiratory conditions.
Absence of control group in our study, is considered to be one of the study weaknesses, as there are no published data in normal predicted distance in 6MWT, in the Saudi population. Moreover, the test was not repeated to assess test reproducibility. Other limitation in this study was the heterogenousity of the studied population. Most published data in 6MWT looked at disease specific groups, which was not considered here. The primary objective was to assess the test safety in our population. The study was not designed to look at the correlation of 6MWT and several demographic and physiological parameters, in a specific group of patients.
Although this study does not allow definite conclusion of the validity of the test in respiratory conditions, the data support the use of such a test, as an additive tool in combination with other physiological parameters, in assessing lung function. Further evidence of the validity and responsiveness of 6MWT in specific diseases should be explored in future clinical trials, to support the wide use of such test in a clinical setting.
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[Table - 1], [Table - 2], [Table - 3]