Sit-to-stand test and 6-min walking test correlation in patients with chronic obstructive pulmonary disease.

BACKGROUND: The 6-min walking test (6MWT) is one of the most commonly used tests to assess exercise capacity during chronic obstructive pulmonary disease (COPD). However, it is a relatively time-consuming test. Many authors assessed the usefulness of simpler methods, as the sit-to-stand test (STST), to estimate exercise capacity.
PURPOSE: To demonstrate the feasibility of STST, in comparison to 6MWT, for the evaluation of functional status in Tunisian COPD patients and evaluate its correlation to the severity of the disease.
METHODS: We studied patients with COPD (Global Initiative for Chronic Obstructive Lung Disease A-D). All patients had plethysmography and manual quadriceps femoris muscle strength evaluation. Each patient completed a 6MWT and a STST. During the tests, dyspnea severity (Borg scale), heart rate, pulsed oxygen saturation, and blood pressure were measured.
RESULTS: In 49 patients with stable COPD (mean age 67.06 ± 8.4 years, mean forced expiratory volume in the first second 46.25% ± 19.64%), 6MWT and STST were correlated with each other (r = 0.47, P = 0.001). During 6MWT and STST, the rise in heart rate, systolic blood pressure, and severity of dyspnea were statistically significant compared to baseline (P < 0.05). However, cardiorespiratory stress was lower after STST than after 6MWT (P < 0.05). A statistically significant positive correlation was noted between the 6MWT distance and forced vital capacity (r = 0.357, P < 0.05). The 6MWT was negatively correlated with dyspnea severity at baseline (r = -0.289, P < 0.05) and with BODE index (r = -0.672, P < 0.01). STST was correlated only with age (r = 0.377, P < 0.01). No correlation was found between both tests and quadriceps femoris strength.
CONCLUSION: As like as 6MWT, STST can determine functional status during COPD. In addition, it is less time consuming and produces less hemodynamical stress compared to 6MWT. STST can be used as an alternative for 6MWT in patients with COPD.

Physical inactivity in daily life is one of the prominent features during chronic obstructive pulmonary disease (COPD).[1234] It leads to a low daily physical activity levels with an increase of social isolation and depression.[5] At present, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines advocates that improvement in functional status should be a major goal in COPD treatment.[6] Several tests are available for evaluation of functional exercise capacity.[7] One of the most used clinical exercise tests is the 6-min walking test (6MWT). It is a practical and well-tolerated test, which is more reflective of daily life activities than cardiopulmonary exercise tests.[8] Other objective methods such as the sit-to-stand test (STST)[9] and the hand-grip strength test[10] could be an alternative to the 6MWT. STST evaluates the ability to stand up from sitting position, which is an essential activity as walking in daily life. During COPD, STST was shown to be correlated to the timed walk distance and to daily physical activity.[1112] Thus, we hypothesize that STST could be used as 6MWT, to determine the functional status in patients with COPD. The present study aims to demonstrate the feasibility of STST, in comparison to 6MWT, for the evaluation of functional status in a Tunisian COPD population and to evaluate its correlation to the severity of the disease.

Methods

Subjects

Patients with mild-to-very severe COPD referred to the Pulmonary Department of University Hospital Rabta of Tunis between January and June 2014 were considered for participation in the study.

The inclusion criteria were:

Male/female subjects aged from 40 to 75 years with confirmed COPD according to GOLD-guidelines.

Clinically stable state for a minimum of 2 weeks having had no recent infectious exacerbations.

The exclusion criteria were:

Chronic respiratory failure with long term oxygen therapy.

A recent coronary syndrome.

Severe hypertension.

Orthopedic pathology with walking difficulty.

Study design

Each patient performed STST and 6MWT, with an interval of 2 h between each test; the sequence of the tests was randomized. Severity of dyspnea on resting and at the end of the STST and 6MWT was evaluated by Borg scale. The study protocol was approved by the local ethic committee. The aim of the study was fully explained to participants, and all gave informed consent.

Methods

6-min walking test

Patients performed the 6MWT according to the guidelines of the American Thoracic Society (ATS).[7] The 6MWT was performed on a 30-meter indoor track while attempting to cover as much distance as possible in the allotted 6-min without supplementary oxygen. An experienced investigator timed the walk and recorded the distance traveled using standardized encouragement strategy. None of the patients used a walking aid in daily life or during the test.

Sit-to-stand test

A standard chair (height 46 cm) with no arm supports was used. Patients were instructed to stand up from and sit down on the chair with no support from the hands, repeating the procedure as many times as possible for the duration of 1-min at a patient defined pace.[9] The test was first demonstrated by a staff member and then performed by the subject. The number of stands during 1-min was determined manually.

Evaluation of the lung function

Pulmonary function tests

Spirometry, whole body plethysmography measurements were performed according to the ATS and the European Respiratory Society guidelines using a Medisoft Bodybox 5500 plethysmograph.[1314] Forced vital capacity (FVC), mean forced expiratory volume in 1 s (FEV1), FEV1/FVC, total pulmonary capacity, and residual volume values were recorded.

Peripheral muscle strength

quadriceps femoris muscle strength was tested with manual muscle test by the use of Daniels 0-5 Grading System in sitting position.[15]

Statistical analysis

A statistical software package was used for all measures (SPSS for Windows, version 11.0, Maasachussets, USA). Descriptive data were expressed as mean and standard deviation. Data comparison among different tests was performed by means of ANOVA. The correlation between results of STST and 6MWT was calculated by Pearson's and Spearman rank correlation coefficient (r). A P < 0.05 was considered significant. Comparisons between baseline and the end of tests were performed by means of the paired t-test. Changes from baseline were computed for each test and compared by means of ANOVA test.

Results

Forty-nine patients with stable COPD (mean age 67.06 ± 8.4 years, mean FEV1 46.25% ± 19.64%) met the inclusion and exclusion criteria and agreed to take part in the study. Anthropometrical characteristics, pulmonary function data, and BODE index (total score) values of the patients are presented in Table 1. Patients reported the following comorbidities: diabetes mellitus (eight patients), hypertension (11 patients), coronary artery disease (three patients), and stroke (one patient). The average tobacco consumption was 59.51 package per year (PA) ± 31.29. Twenty-five patients declared they were active smokers. COPD was mild (GOLD I) in 6%, moderate (GOLD II) in 36%, severe (GOLD III) in 34%, and very severe (GOLD IV) in 24% of the patients. The majority of patients (63.2%) were “at high risk and with high symptom burden” (GOLD D). The mean degree of dyspnea on Borg scale was 4.61 ± 2.1. The mean 6MWT distance was 449.08 m ±131.88. The mean number of stands during STST was 19.31 ± 5.56. Results of 6MWT, STST, and quadriceps femoris strength are presented in Table 2. Significant increase in dyspnea severity, heart rate, and systolic blood pressure were noted during 6MWT and STST [P < 0.05, Table 3]. However, STST was less hemodynamically stressful than 6MWT (P < 0.05). The pulsed saturation did not significantly change during the two tests [P > 0.05, Table 3]. There was a statistically significant positive correlation between the 6MWT distance and the number of stands during the STST [r = 0.47, P = 0.001; Figure 1]. There was a statistically significant negative correlation between the 6MWT distance with dyspnea severity at baseline [r = −0.289, P < 0.05; Table 4] and with BODE index [r = −0.672, P < 0.01; Table 4]. A statistically significant positive correlation was noted between the 6MWT distance with FVC [r = 0.357, P < 0.05; Table 4]. Number of stands during STST was associated only with age [r = −0.377, P < 0.01; Table 4]. No correlation was found between both tests and quadriceps femoris strength [P > 0.05, Table 4].

Table 1

Baseline patient characteristics

Table 2

Results of STST and 6MWT

Table 3

Change of cardiorespiratory parameters during the STST and 6MWT

Figure 1

Correlation between the 6-min walking test distance and number of stands during sit-to-stand test

Table 4

Correlation between STST and 6MWT and some parameters

Discussion

The number of published studies measuring functional status during COPD is increasing rapidly over the past years.[9] It reflects clinician's awareness about functional status during COPD. Improvement of daily physical and social activities is now one of the most pertinent clinical issues in the COPD management.[6] In clinical practice, functional status can be measured by several different methods. According to Kocks et al., measurement tools of functional status can be categorized into: Laboratory tests (e.g.,: Cycle ergometry), semi-laboratory tests (e.g.,: The 6MWT), field tests (e.g.,: The accelerometer), and patient-reported consequences (e.g.,: MMRC dyspnea scale and the St. George's Respiratory Questionnaire).[9] The 6MWT is one of the most reliable semi-laboratory tests. It is standardized, easy to perform, and well tolerated.[7] Moreover, the time walking distance is a strong predictor of survival in patients with COPD.[8161718192021] However, the most important barrier for the use of 6MWT is that it requires trained staff, space, and equipment, which is not commonly available in many practice settings.[722] Over the last years, a significant amount of research has been performed to explore simpler tests like STST, to measure exercise capacity. Initially, STST was essentially used to determine the functional status of elderly patients with orthopedic diseases.[232425262728] Later, it was demonstrated that, during COPD, STST is strongly associated with time walking distance, mortality, and with BODE Index.[12293031] These data lead us to hypothesize that STST could be used to determine the functional state of Tunisian patients with COPD. Our results show that 6MWT distance and the number of stands during STST were significantly correlated with each other. Several authors investigated the usefulness of simpler and less time-consuming tests than 6MWT, to assess daily activity during COPD. They found that, like the 6MWT distance, the number of stands during STST is correlated to daily activity.[1132] In addition, as suggested by our results, STST is better tolerated and produces less hemodynamic stress compared to the 6MWT. Therefore, STST is a reliable and practical test that could be used for mild to moderate COPD to assess functional status.

During COPD, dyspnea is one of the strongest correlates of impaired exercise performance.[33] As shown in our study, perceived breathlessness is correlated with walking distance in patients with COPD.[172134] Unlike dyspnea, FEV1 is known to be a poor predictor of symptoms and disability during COPD.[16193334] Our results demonstrated that there is no significant correlation between COPD severity (FEV1) and functional status (STST and 6MWT). These results lead us to emphasize that during COPD, functional tests are essential in order to assess patient's disability. This information cannot be obtained only from traditional functional findings.[173335]

More than lung function or dyspnea, exercise capacity is consistently correlated with mortality during COPD.[3637] The BODE Index is considered to be the best predictor of survival in patients with COPD.[38] Many authors showed a correlation between the BODE index and variables assessed during the 6MWT and STST in moderate to very severe COPD patients.[2938] Our study demonstrated a statistically significant negative correlation between the BODE index and the 6MWT distance.

It has been recognized that skeletal muscle dysfunction is a common feature in patients with COPD.[39] Peripheral muscle weakness affects the results of performance in these patients.[18] 6MWT and STST are able to identify peripheral muscle weakness during COPD.[28404142] Unexpectedly, our study showed no correlation between functional status (6MWT, STST) and muscle strength. The relative muscle strength preservation in our patients could explain these findings. Moreover, quadriceps femoris muscle strength was tested manually by a physiotherapist. Use of more objective tests like the hand-grip test, may be more appropriate to accurately assess muscle strength.

Conclusion

This study proves that STST, like 6MWT, correctly determines the functional status in patients with COPD. Moreover, STST is less hemodynamically stressful and easier to apply compared to 6MWT. Thus, although STST was not correlated to COPD severity, these findings led us to emphasize the use of STST as an alternative of 6MWT to assess the functional capacity in patients with COPD.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.