|Year : 2014 | Volume
| Issue : 2 | Page : 115-120
Relationship between exercise capacity and clinical measures in patients with chronic obstructive pulmonary disease
Maryam Bakhshandeh bavarsad1, Abdolali Shariati2, Esmaeil Idani3, Mahmud Latifi4
1 Department of Nursing, School of Nursing and Midwifery, Lorestan University of Medical Sciences, Khorramabad, Iran
2 Department of Nursing, School of Nursing and Midwifery, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
3 Department of Internal Medicine, Pulmonary Unit, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
4 Department of Statistics, School of Public Health, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
|Date of Web Publication||9-Oct-2014|
School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Golestan Blv, Ahvaz
Context: The 6-min walk distance test (6MWT) is commonly used to assess the exercise tolerance and to identify functional changes resulting from disease progression or therapeutic intervention in patients with chronic obstructive pulmonary disease (COPD). Understanding the factors related to exercise capacity can create a way to a better understanding of physical activity limitations. Aims: The aim of this study was to determine the relationship between 6MWT, dyspnea, quality of life (HRQL), and disease severity and identify the predictors of 6MWT in COPD patients. Settings and Design: A cross-sectional study was developed on COPD patients referred to the outpatient pulmonary clinic of the Ahvaz Jundishapur University of Medical Sciences. Materials and Methods: A total of 72 patients with mild to very severe COPD participated in this study. The 6MWT was performed based on American Thorax Society's protocol. Disease severity was evaluated using spirometry. The health-related quality of life (HRQL) was assessed by the St George's Respiratory Questionnaire (SGRQ), and exertional dyspnea was measured by Borg score. Statistical Analysis Used: The data were evaluated using Pearson's linear correlation coefficient, Spearman's correlation coefficient, and multivariate linear regression. Results: The 6-min walk distance (6MWD) correlated positively with forced expiratory volume in 1 s (FEV 1 ) (r = 0.36, P < 0.05) and forced vital capacity (FVC) (r = 0.37, P < 0.05), whereas there was no significant correlation between disease severity based on Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification and 6MWD. Moreover, no statistically significant correlation was found between exertional dyspnea and 6MWT. A negative correlation was observed between 6MWD and total score of QOL, activity, and impact domain, respectively (r = −0.39, r = −0.44, r = −0.40, P < 0.01). Multiple regression analysis indicated that the age was identified as independent predictor of the 6MWD. Conclusions: This study showed that there is stronger relationship between 6MWD and HRQL (activity and impact) compared with physiological measures of disease severity such as FEV 1 .
العلاقة بين القدرة على ممارسة الرياضة و القياسات السريرية في المرضى الذين يعانون مرض الانسداد الرئوي المزمن.
مقدمة: المرضى الذين يعانون مرض الانسداد الرئوي المزمن عادة ما يستخدم معهم اختبار السير على الأقدام لمدة ست دقائق لتقييم احتمالهم للتدريب . ويعد فهم العوامل التي تتعلق بالقدرة على ممارسة الرياضة وسيلة أفضل لفهم قيود النشاط البدني.
الأهداف: كان الهدف من هذه الدراسة تحديد العلاقة بين اختبار المشي لمدة ست دقائق على الأقدام وضيق التنفس وشدة المرض ومدى إمكانية التنبؤات في اختبار السير على الأقدام لمدة ست دقائق مع مرضى الانسداد الرئوي المزمن.
المواد ومنهج البحث: أجريت الدراسة على المرضي المصابون بمرض الانسداد الرئوي المزمن المحولين للعيادة الخارجية من جامعة الأهواز للعلوم الطبية في جنديسابور . اختير لهذه الدراسة 72 مريضا يعانون مرض الانسداد الرئوي تتراوح حالاتهم بين خفيفة إلى حادة جدا .و أخضعوا لاختبار السير على الأقدام لمدة ست دقائق عل غرار بروتوكول جمعية الصدر الأمريكية وتم تقييم شدة المرض باستخدام قباس التنفس . و تم تقييم صحة المرضى وعلاقتها بنوعية الحياة باستخدام استبانة سانت جورج لقياس التنفس. وتم قياس ضيق التنفس الجهدي باستخدام معدل بورج.
التحليلات الإحصائية:تم تحليل البيانات باستخدام اختبار ارتباط بيرسون الخطي، و اختبارارتباط سبيرمان ، و الانحدار الخطي متعدد المتغيرات.
النتائج والاستنتاج:ارتبط اختبار السير عل الأقدام لمدة ست دقائق ارتباطا إيجابيا مع حجم الزفير القسري في ثانية واحدة ، في حين لم هنالك ارتباط كبير بين شدة المرض على أساس المبادرة العالمية لمرض الانسداد الرئوي المزمن (GOLD) وعليه ابتت الدراسة غلاقة ارتباطية قوية بين 6MWD and HRQLقياس خصائص الجهاز التنفسى FEV1
Keywords: Chronic obstructive pulmonary disease, dyspnea, exercise capacity, quality of life, 6-min walk distance test
|How to cite this article:|
bavarsad MB, Shariati A, Idani E, Latifi M. Relationship between exercise capacity and clinical measures in patients with chronic obstructive pulmonary disease
. Saudi J Sports Med 2014;14:115-20
|How to cite this URL:|
bavarsad MB, Shariati A, Idani E, Latifi M. Relationship between exercise capacity and clinical measures in patients with chronic obstructive pulmonary disease
. Saudi J Sports Med [serial online] 2014 [cited 2021 Jun 25];14:115-20. Available from: https://www.sjosm.org/text.asp?2014/14/2/115/142363
| Introduction|| |
Chronic obstructive pulmonary disease (COPD) is an irreversible disease with chronic airflow limitation.  It is one of the major causes of mortality and morbidity worldwide.  COPD patients suffer from relatively severe dyspnea and disability despite disease severity.  These problems are usually the reason for seeking medical services. 
Exercise capacity is one of the most important physiologic measures in COPD patients.  It can potentially evaluate various limitations and recognize their contributing factors.  There are some methods for measuring exercise capacity, one of them is 6-min walk distance test (6MWT). This measure is used for assessing functional status, and it can predict the prognoses of various respiratory conditions.  For many patients with COPD, psychosocial factors may interact with physiologic abnormalities to limit exercise capacity. 
Many studies have assessed the relationship between exercise capacity and lung function; most of them show that there is a weak correlation between exercise capacity and the degree of airway obstruction. , This finding explains that other factors, except lung function, play an important role in limiting exercise capacity in COPD patients.  Exercise capacity in patients with COPD has several determinants.  Therefore, understanding the exercise capacity predictors can be a way to better understand physical activity limitations;  the aim of this study is to examine the relationship between dyspnea, quality of life (QOL), disease severity, and 6MWT to determine those clinical variables predicting functional exercise capacity in patients with COPD.
| Subjects and methods|| |
This was cross-sectional study involving 72 samples (66 men and 6 women) with COPD, referred to the outpatient pulmonary clinic of the Ahvaz Jundishapur University of Medical Sciences. The sample includes all individuals who have inclusion criteria in 8-months sampling. The study design was approved by the ethics of research committee of the Jundishapur University of Medical Sciences (ruling number: U89295).
The inclusion criteria were as follows: Having been diagnosed with mild to very severe COPD, according to Global Initiative for Chronic Obstructive Lung Disease (GOLD),  being 40-70-years-old, and presenting stable clinical condition without episodes of exacerbation in the preceding month. Exclusion criteria included: Comorbid condition likely to reduce exercise capacity such as unstable angina and myocardial infarction during previous month  and body mass index (BMI) >35 kg m-  , weaning dose of oral corticosteroids, having cognitive deficit and musculoskeletal disorders, increasing forced expiratory volume in 1 s (FEV 1 ) greater than or equal to 12% following bronchodilator (salbutamol) therapy, and consuming bronchodilator during the 6MWT.
Pulmonary function tests were performed using a Spirolab II (made in Italy) at the outpatient clinic. The health-related quality of life (HRQL) was assessed by Persian version of the St George's Respiratory Questionnaire (SGRQ) and Cronbach's alpha was calculated 0.93.  Three component scores were calculated for the SGRQ: (1) symptoms included eight questions about respiratory problems, frequency, and severity (e.g. cough, breathlessness, secretion and so forth), (2) activity included two questions about activities that cause dyspnea (e.g. taking shower, walking, dressing and so forth), and (3) impact included seven questions about how respiratory disease interfere in the daily living activities and how to influence the psychosocial functioning.  The each component is calculated from the summed weights for the positive responses to its questions. The total score is calculated by summing the scores of three domains of the questionnaire. The result expressed as a percentage, 100% indicated the worst and 0% indicated the best QOL. The questionnaire was completed by patients if they had literacy; for illiterate patients, conducted interview was used and questions were explained clearly for better understanding.
The exertional dyspnea was measured by Borg scale,  ranging from 0 (not noticeable) to 10 (maximum dyspnea), immediately after 6MWT.
The 6MWT was performed according to American Thoracic Society Guidelines (ATS).  The patients had practiced the 6MWT on two occasions for familiarity with the exercise test and the best one was recorded as the 6MWT. The patients remained seated for 10 min before and after the walk test; after the rest period, arterial blood pressure was measured with a sphygmomanometer and a stethoscope, arterial oxygen saturation and heart rate were assessed with pulse oximetry (NONIN, Ganshorn, USA). The test was performed indoors, along a flat straight corridor with 30-m length. The length of corridor was marked every 3 m. The patients were encouraged to walk as far as they could in 6 min. Standard phrases of encouragement were used at particular time intervals during the test. The distance covered was measured as 6-min walk distance (6MWD).
Data were analyzed using the Statistical Package for the Social Sciences, version 16.0 (SPSS 16). Data are expressed as mean ± standard deviation (SD). The relationship between numerical variables was examined using Pearson's linear correlation coefficient, and Spearman's correlation coefficient was used to determine the association between two ordinal or nominal variables. Multivariate linear regression analysis was used to determine predictors of the 6MWD. The variables found to be significant (P < 0.05) on univariate analysis were included in multivariate linear regression. The level of statistical significance was set at P < 0.05.
| Results|| |
A total of 72 patients (66 males, 6 females) with COPD participated in this study. Demographic data and the baseline lung function are summarized in [Table 1]. The two factors that worsen the COPD are occupation dusts and smoking, 28 patients (38.9%) had job contamination (e.g. agronomy, steel workers, and oil company workers), 28 patients (38.9%) were current smokers, 28 patients (38.9%) were ex-smokers, and 16 patients (22.2%) were nonsmokers.
[Table 2] shows severity of COPD based on GOLD. 
|Table 1: Demographic data and baseline lung function parameters for subjects with COPD (N=72)|
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The mean (SD) 6MWT was 455.4 (79.5) m, this was 35.7% (253 m) lower than the expected value (708.7 m), this difference was statistically significant (P = 0.000). The predicted 6MWT distance was calculated according to the reference equation by Enright et al.,  using patient's age, sex, weight, and height. The mean (SD) SGRQ total score was 41.2 (18.4) and mean (SD) three dimension of SGRQ; symptom, activity, and impact were 46.5 (24.9), 57.7 (21.7), and 29.7 (19.6), respectively. It should be noted that higher scores indicate worse QOL.
Relationships between clinical measures and exercise capacity
There was no relationship between 6MWT, BMI, and severity of disease [Table 3]. Spirometric measures correlated weakly with the 6MWT, showing that persons with less airway obstruction had better exercise capacity. We found that heart rate before walking test presented a negative correlation with 6MWT [Table 3]. No statistically significant correlation was found between exertional dyspnea and 6MWT. Except for symptoms, other dimensions (activity and impact) correlated with 6MWT. Activity dimension correlated more than total score and impact with 6MWT [Table 3]. The variables found to be significant on univariate analysis were included: Age, weight, pack/year, FEV 1 L , forced vital capacity (FVC) L, pulse rate before 6MWT, O 2 saturation before 6MWT, QOL total, and activity and impact domains. Multivariate linear regression was done by these factors. The age was identified as an independent predictor of the 6MWD. A higher 6MWD was associated with lower age.
| Discussion|| |
Our result showed that 6MWT in COPD patients is 35.7% lower than the expected value. De Torres and coworkers reported that limitations of COPD make it difficult to do low-resistance activities such as 6MWT.  Carters and coworkers  showed the ventilatory limitation to exercise in COPD patients based on physiologic gas exchange data; our study and the same studies supported this finding by showing the significant relationship between 6MWT and FEV1. , Enfield and et al., reported that 6MWT was positively related with the length of survival period; it means that survival period was longer among the COPD patients who displayed higher 6MWD value.  These relationships showed that the 6MWT can help in the assessment of pulmonary function and survival in patients with COPD. Although there is a relationship between 6MWT and FEV 1 , it is a weak correlation, ,, which consequently limits the use of the FEV 1 as sole indicator of severity and prognoses of disease.
Forced Expiratory Flow (FEF) from 25-75% shows the level of small airway obstruction. Our finding revealed that there is no relationship between FEF 25-75 and 6MWD. Inal-Ince et al.,  and Pineda et al.,  showed that degree of small airway obstruction contributed to external work of walking rather than the distance; their findings supported our result.
Age is a key factor influencing the exercise capacity; , in our study there was a strong negative correlation between age and 6MWD.
This study revealed that there was no significant correlation between 6MWD and exertional dyspnea. Oga and coworkers showed that all of the indices of exercise capacity that included progressive cycle ergometry, 6MWD, and cycle endurance test had moderately correlated with the clinical dyspnea measured by oxygen cost diagram. However, only cycle endurance test showed weak correlation with the Borg score at the end of test.  Inal-Ince and coworkers showed a significant correlation between dyspnea and 6MWT. In their study, the patients' disease was moderately in severe and very severe disease stage,  but in our study, COPD patients were mainly in mild to moderate stages, and probably in these stages, Airway obstruction does not play an important role in the development of dyspnea. Moreover, de Torres showed that women with COPD report more functional dyspnea than men with the same degree of airway obstruction.  Most of our samples were men because in Iranian culture women are not expected to smoke. Low number of women sample and most patients with mild to moderate disease severity seem to cause not seen correlation between 6MWT and dyspnea in our study.
Our result showed a significant correlation between QOL and dyspnea. Negative correlation between SGRQ domains (activity and impact) and 6MWT is the result of limited functional and physical activity of the studied patients.  We also observed that the activity score correlated better with 6MWT as previously reported. , This finding displayed that walking test reflects a good measure of the daily living activities of COPD patients.
No significant correlation was seen between 6MWT and symptom score of the SGRQ, which is consistent with the previous studies. ,,
We found that the number of heart rate before the test had negative correlation with 6MWD, so that increased heart rate before walking causes intolerance activity in COPD patients. One way to improve the exercise capacity can be the control of heart rate in the normal range. Camillo and coworkers found that cardiac autonomic function of patients with COPD is not related to disease severity but mainly to the level of physical activity in daily life. 
Our result showed a positive correlation between 6MWT and SPO 2 before and after walking test; this means that both the desaturations at the baseline and during the walking test affect the passed distance so that oxygen therapy before and during the activity can improve exercise performance in patients with COPD, which is consistent with findings of Chatila et al.  Casanova and coworkers showed that the 6MWD helps predict mortality primarily in patients with severe COPD, although the oxygen desaturation profile during the 6MWT improves the predictive ability of the 6MWD. 
The limitations of this study are the following: The small number of subjects recruited, especially women sample; all of patients who have inclusion criteria in 8-months sampling were selected, in Iran there are no specific places for screening and diagnosing these patients so that most of people that referred to the clinic or hospitals had an exacerbation of disease and not suitable for 6MWT, the majority of those who demonstrated mild to moderate COPD; and no assessment of respiratory muscle strength.
In conclusion, this study indicates that the 6MWD provides valuable information of functional status in a group of patients with mild to very severe COPD. Our results showed that there is a stronger relationship between 6MWD and HRQL (activity and impact) compared with physiological measures of disease severity such as FEV 1 . Therefore, organizing management strategies to improve exercise tolerance have a positive impact on HRQL in this patient's population.
| Acknowledgment|| |
We thankfully acknowledge the Deputy of Research Affairs at the Ahvaz Jundishapur University of Medical Sciences for the financial and technical support for this research and patients for their participation in this study.
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[Table 1], [Table 2], [Table 3]