Abstracts
Objectives:
to evaluate the concurrent validity of the six-minute step test (6MST) in assessing exercise capacity of COPD patients using the six-minute walk test (6MWT) as a gold-standard. The predictive validity of the 6MST was assessed to determine a cut-off point for identification of low exercise capacity.
Method:
thirty-two COPD patients (50-87 years old) with mild to very severe obstruction performed the 6MST and 6MWT twice.
Results:
Concurrent validity: a strong positive correlation (Pearson) between the number of ascents on the first (T1), second (T2) and the best of both (T1 or T2) tests during the 6MWT was observed. Although a moderate negative correlation with BODE index and FEV1 was found, it was considered insufficient to test the validity, therefore ROC curves were not applied. The predictive validity (ROC) of the 6MST to identify low physical capacity (compared with the 6MWT) using the performance of T1 or T2, or solely T1 was considered accurate, and the area under the curve was 0.8 (IC95% 0.62-0.98) and 0.85 (IC95% 0.70-0.99), respectively. To classify patients, the cut-off points of 86 and 78 steps were chosen, with both values showing 90% of sensitivity and specificity of 64% and 68% for T1 or T2, or solely T1, respectively.
Conclusion:
The number of steps on the 6MST was valid to verify exercise capacity in COPD patients and the cut-off point of 78 steps was able to identify patients with poor exercise tolerance. Values under this cut-off point are considered to identify patients with a poorer prognosis.
COPD; physical therapy; validity; exercise test
Objetivos:
Avaliar a validade concorrente do desempenho no teste de degrau de seis minutos (TD6) em analisar a capacidade física da DPOC, relacionando-o com o teste de caminhada de seis minutos (TC6), bem como verificar a presença de validade de critério preditiva do TD6, determinando um valor de corte para identificar baixa capacidade física.
Método:
Trinta e dois pacientes com DPOC estágios leve-muito grave, de ambos os sexos, entre 50-87 anos, realizaram dois TD6 e dois TC6.
Resultados:
Validade concorrente: observou-se correlação forte positiva (Pearson) entre o número de subidas do primeiro (T1), segundo (T2) e do melhor dos dois (T1 ou T2) TD6 com a distância percorrida no TC6. Embora constatamos correlações negativas entre os desempenhos no TD6 com o índice BODE e VEF1, essas não foram suficientes para caracterizar validade, não sendo traçadas as curvas ROC. A validade preditiva (curvas ROC) do TD6 para identificar baixa capacidade física (comparação com o TC6), utilizando o desempenho do T1 ou T2 ou somente do T1, foi considerada acurada para alguns propósitos, sendo a área abaixo da curva de 0,8 (IC95% 0,62-0,98) e 0,85 (IC95% 0,70-0,99), respectivamente. Para classificar os pacientes, escolhemos o ponto de corte de 86 e 78 degraus, apresentando sensibilidade de 90% e 90% e especificidade de 64% e 68%, para T1 ou T2 e somente T1, respectivamente.
Conclusão:
O desempenho no TD6 apresentou-se válido para verificar capacidade física na DPOC e identificou pacientes com baixa capacidade física, utilizando como ponto de corte 78 degraus, em que valores abaixo disso representaram pior prognóstico.
DPOC; fisioterapia; validade dos testes; teste de esforço
Introduction
Chronic obstructive pulmonary disease (COPD) is characterized by decreased aerobic
capacity11. Dourado VZ, Tanni SE, Vale SA, Faganello MM, Sanchez FF, Godoy I.
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2006;32(2):161-71. PMid:17273586. and muscle strength22. Spruit MA, Franssen FM, Rutten EP, Wagers SS, Wouters EF. Age-graded
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, culminating in loss of functionality and exercise intolerance. These changes
are the most important consequences of this disease33. Corrêa KS, Karloh M, Martins LQ, Santos K, Mayer AF. Can the glittre
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, which negatively impacts the quality of life of patients11. Dourado VZ, Tanni SE, Vale SA, Faganello MM, Sanchez FF, Godoy I.
Systemic manifestations in chronic obstructive pulmonary disease. J Bras Pneumol.
2006;32(2):161-71. PMid:17273586.. Therefore, it is necessary to evaluate exercise tolerance in COPD patients
through functional tests, since the tests are able to provide specific information
concerning functional capacity and physiological adaptation during physical effort.
The maximal cardiopulmonary test is considered the gold-standard for assessing exercise
tolerance because it evaluates functional capacity and abnormal responses of the
musculoskeletal, cardiovascular and respiratory systems. In addition, it has been widely
used in the prescription and monitoring of physical training in cardiac and pulmonary
rehabilitation44. Neder JA, Nery LE. Teste de exercício cardiopulmonar. J Bras Pneumol.
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. However, its use is limited in clinical practice due to the complexity of the
equipment, high costs and the need for trained technicians66. Cataneo DC, Cataneo AJM. Acurácia do teste de escada utilizando o
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.
Therefore, alternative forms of assessment to the maximal test, such as the 6-minute
walk test (6MWT) and the 6-minute step test (6MST) began to stand out for being
practical and easy to perform in clinical settings77. American Thoracic Society - ATS. American Thoracic Society statement:
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88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
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interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
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. The 6MWT is a test that has been used in different populations99. Pires SR, Oliveira AC, Parreira VF, Britto RR. Teste de caminhada de
seis minutos em diferentes faixas etárias e índice de massa corporal. Rev Bras
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walk distance, peak oxygen uptake, and mortality in COPD. Chest. 2007;132(6):1778-85.
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1313. Enfield K, Gammon S, Floyd J, Falt C, Patrie J, Platts-Mills TA, et
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and is considered valid and reproducible. In addition, it is a good predictor of
morbidity and mortality of patients with COPD1212. Cote CG, Pinto-Plata V, Kasprzyk K, Dordelly LJ, Celli BR. The 6-min
walk distance, peak oxygen uptake, and mortality in COPD. Chest. 2007;132(6):1778-85.
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1414. Casanova C, Cote C, Marin JM, Pinto-Plata V, Torres JP,
Aguirre-Jaíme A, et al. Distance and oxygen desaturation during the 6-min walk test
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. In a recent and large cohort of 2110 COPD patients Spruit et al.15 15. Spruit MA, Polkey MI, Celli B, Edwards LD, Watkins ML, Pinto-Plata
V, et al. Predicting outcomes from 6-minute walk distance in chronic obstructive
pulmonary disease. J Am Med Dir Assoc. 2012;13(3):291-7. Pmid:21778120.
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determined the distance of 334 m as a predictor of mortality. In a period of
three years, 62.5 % of the patients with values below this performance level died,
emphasizing the importance of the prognostic value. Despite the advantages presented in
relation to the 6MWT, the physical space requirements for its implementation is
sometimes a limiting factor77. American Thoracic Society - ATS. American Thoracic Society statement:
guidelines for the six-minute walk test. Am J Respir Crit Care Med.
2002;166(1):111-7. PMid:12091180.
http://dx.doi.org/10.1164/ajrccm.166.1.at1102
http://dx.doi.org/10.1164/ajrccm.166.1.a...
,
88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
Pereira CA, et al. A step test to assess exercise-related oxygen desaturation in
interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
http://dx.doi.org/10.1183/09031936.00094006
http://dx.doi.org/10.1183/09031936.00094...
, especially in primary care. Thus, finding alternative solutions are
important.
On the other hand, the 6MST consists of a self-paced test performed on a step with fixed
dimensions and it is considered a simple and effective alternative because it requires
less physical space in addition to being portable88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
Pereira CA, et al. A step test to assess exercise-related oxygen desaturation in
interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
http://dx.doi.org/10.1183/09031936.00094006
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,
1616. Neder JR, Nery LE. Fisiologia clínica do exercício. São Paulo: Artes
Médicas; 2003..
Studies conducted for nearly 80 years have shown the importance of step tests in the
evaluation of physical fitness of healthy individuals by detecting possible
abnormalities in physiological responses1717. Master AM, Oppenheimer ETB. A simple exercise tolerance test for
circulatory efficiency with standard tables for normal individuals. Am J Med Sc.
1929;177(2):223-43. http://dx.doi.org/10.1097/00000441-192902000-00010
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1818. Andrade CHS, Cianci RGC, Malaguti C, Dal Corso S. O uso de testes do
degrau para a avaliação da capacidade de exercício em pacientes com doenças
pulmonares crônicas. J Bras Pneumol. 2012;38(1):116-24. PMid:22407048.
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. Schnaider and Karsten1919. Schnaider J, Karsten M. Testes de tolerância ao exercício em
programa de fisioterapia hospitalar após exacerbação da doença pulmonar obstrutiva
crônica. Fisioter Mov. 2006;19(4):119-26. observed that the performance of hospitalized patients with COPD when doing the
6MST showed good correlation with the 6MWT, suggesting that it could replace the 6MWT in
a hospital environment. Machado et al.2020. Machado NC, Natali V, Squassoni SD, Santana VT, Baldin AC, Fiss E.
Estudo comparativo entre os resultados do teste de caminhada de seis minutos e do
degrau de seis minutos em pacientes com doença pulmonar obstrutiva crônica. Arq Med
ABC. 2008;32(Suppl. 2):S47-50. found significant correlations between oxygenation, fatigue of the lower limbs
(LL) and diastolic blood pressure at the peak of these two tests and concluded that the
6MST could be an alternative to the 6MWT.
Recently, the 6MST was validated in patients with interstitial lung disease88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
Pereira CA, et al. A step test to assess exercise-related oxygen desaturation in
interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
http://dx.doi.org/10.1183/09031936.00094006
http://dx.doi.org/10.1183/09031936.00094...
. The study showed that it is reproducible in addition to it being safe and
sensitive to oxygen desaturation induced by exercise, easy to use, economical and
portable88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
Pereira CA, et al. A step test to assess exercise-related oxygen desaturation in
interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
http://dx.doi.org/10.1183/09031936.00094006
http://dx.doi.org/10.1183/09031936.00094...
. However, there are currently no guidelines for the use of 6MST in patients with
COPD2121. Global Strategy for the Diagnosis, Management, and Prevention of
Chronic Obstructive Pulmonary Disease - GOLD. 2012. and the literature lacks concurrent validity and predictive criterion of this
test in patients with COPD.
Therefore, the objectives of this study were to assess the concurrent validity of the number of steps on the 6MST in physical capacity of patients with COPD using the 6MWT as the gold-standard test, as well as to verify the predictive validity criterion of the 6MST by determining the cut-off value to identify patients with low exercise capacity and consequently a poor prognostic outcome.
Method
Study subjects
The present study is part of a major observational, prospective, cross-sectional study, conducted at the Laboratory of Spirometry and Respiratory Physical Therapy, Universidade Federal de São Carlos (UFSCar), São Carlos, SP, Brazil. The major study was designed to examine the clinimetric properties (validity and reliability) of the 6MST and 6MWT in three different populations (patients with COPD, young adults, and elderly). The study was registered in Clinical Trials. Gov. (NCT01298661). The present study specifically aimed to determine the validity of the 6MST in patients with COPD.
Thirty-four subjects ( patients), aged 50 to 87 years, of both sexes, and referred for care at the Special Unit of Respiratory Therapy - UFSCar - during the period June 2011 to July 2012, were included in the study. The participants were invited through posters in the university and neighbourhood, by local radio, television and newspapers. Participants were contacted by phone and were invited to participate in the study if they fit the inclusion criteria.
Inclusion criteria were as follows: clinical and spirometric diagnosis of COPD, obstruction ranging from mild to very severe2121. Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Pulmonary Disease - GOLD. 2012., clinically stable and with no history of infection or exacerbation of respiratory symptoms in the last three months preceding the study. The exclusion criteria were: patients with exacerbated lung disease, decompensated heart disease, neuromuscular, rheumatic and orthopedic diseases that prevented performance of the exercise tests, controlled hypertension without the use of beta-blockers, those who did not complete one of the tests and those with peripheral oxygen saturation (SpO2) below 80% of physical efforts.
All participants signed a consent form, the same used in the major study, which described all evaluations and analyses used in the present study. The major study was approved by the Research Ethics of UFSCAR (Protocol No. 009/2011).
Experimental protocol
All patients were submitted to a two day assessment, with a minimum interval of 48 hours between them. On the first day, anthropometric characteristics, vital signs, medications used, family history, smoking habits, presence of cough and dyspnea were obtained. In addition, one of the tests, 6MST or 6MWT, with the order determined by lottery, were conducted. On the second day, body composition was assessed as well as the test that was not drawn on the first day.
Six-minute walking test (6MWT)
The 6MWT was performed along a level corridor 30 meters long and 1.5 meters wide.
Patients were instructed and encouraged to walk as far as possible in six minutes,
using standard incentive phrases every minute77. American Thoracic Society - ATS. American Thoracic Society statement:
guidelines for the six-minute walk test. Am J Respir Crit Care Med.
2002;166(1):111-7. PMid:12091180.
http://dx.doi.org/10.1164/ajrccm.166.1.at1102
http://dx.doi.org/10.1164/ajrccm.166.1.a...
. The 6MWT was performed twice on the same day with an interval of 30 minutes
between the tests. The distance covered in each test was used for analysis.
SpO2 (Nonin(r), model 2500, Minneapolis, Mn, USA), heart rate
(HR, Polar(r) Vantage NVTM, Model 1901001, Kempele, Oulu, Finland),
symptoms of dyspnea and fatigue of the lower limbs were verified by the Borg modified
scale CR102222. Borg GA. Psychophysical bases, of perceived exertion. Med Sci Sports
Exerc. 1982;14:377-81. PMid:7154893.
http://dx.doi.org/10.1249/00005768-198205000-00012
http://dx.doi.org/10.1249/00005768-19820...
. Blood pressure (BP) was obtained at rest and immediately after testing.
Six-minute step test (6MST)
The 6MST was carried out by two raters: one to control the test and the other to
count the steps. A step (20 cm high with non-slip rubber surfave)88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
Pereira CA, et al. A step test to assess exercise-related oxygen desaturation in
interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
http://dx.doi.org/10.1183/09031936.00094006
http://dx.doi.org/10.1183/09031936.00094...
was used as the test device. For better reproducibility, the 6MWT test
followed the principles of the American Thoracic Society77. American Thoracic Society - ATS. American Thoracic Society statement:
guidelines for the six-minute walk test. Am J Respir Crit Care Med.
2002;166(1):111-7. PMid:12091180.
http://dx.doi.org/10.1164/ajrccm.166.1.at1102
http://dx.doi.org/10.1164/ajrccm.166.1.a...
, using standardized phrases every minute to encourage the patient. Patients
were instructed to step up and down for six minutes, targeting the maximum number of
steps (free cadence). Patients could alternate the lower limbs but upper limbs had no
support and remained stationary alongside the body.
Like at the 6MWT, the SpO2, HR, BP and symptoms of dyspnea and fatigue of
the LL2222. Borg GA. Psychophysical bases, of perceived exertion. Med Sci Sports
Exerc. 1982;14:377-81. PMid:7154893.
http://dx.doi.org/10.1249/00005768-198205000-00012
http://dx.doi.org/10.1249/00005768-19820...
were verified at rest, immediately after the tests and during the recovery
period. The performance on the test (number of steps) was used for analysis.
Assessment of body composition
Body composition was performed through a balance of bioelectrical impedance of
bipolar technology (Tanita(r) model CB-553, Illinois, USA). Analysis of
body mass and muscle mass (MM)2323. Mendes CCT, Raele R. Avaliação corporal por bioimpedância. Rev Nutr
Pauta. 1997;24:12-4. followed by body mass index (BMI) = body weight (kg) / height2 (m)
and fat-free mass index (FFMI) = MM (kg) / height2 (m)2424. Vermeeren MAP, Creutzberg EC, Schols AMWJ, Postma DS, Pieters WR,
Roldaan AC, et al. Prevalence of nutritional depletion in a large out-patient
population of patients with COPD. Respir Med. 2006;100(8):1349-55. PMid:16412624.
http://dx.doi.org/10.1016/j.rmed.2005.11.023
http://dx.doi.org/10.1016/j.rmed.2005.11...
, were calculated.
Pulmonary function test
A pre and post-bronchodilator was conducted by the pulmonologist in order to verify
the degree of obstruction, according to the guidelines of the American Thoracic
Society/European Respiratory Society (ATS/ERS)2525. Miller MR, Crapo R, Hankinson J, Brusasco V, Burgos F, Casaburi R,
et al. ATS/ERS task force: standardisation of lung function testing. Eur Respir J.
2005;26:319-38. PMid:16055882. http://dx.doi.org/10.1183/09031936.05.00034805
http://dx.doi.org/10.1183/09031936.05.00...
. The values obtained were compared to those expected for the Brazilian
population2626. Pereira CAC, Sato T, Rodrigues SC. Novos valores de referência para
espirometria forçada em brasileiros adultos de raça branca. J Bras Pneumol.
2007;33(4):397-406. PMid:17982531.
http://dx.doi.org/10.1590/S1806-37132007000400008
http://dx.doi.org/10.1590/S1806-37132007...
.
BODE index
Patients with COPD were assessed in all necessary measures to calculate the BODE
index. This multidimensional index is composed by the BMI, the degree of airway
obstruction (FEV1% expected post-bronchodilator)21.26, dyspnea (dyspnea
scale from the Medical Research Council)2727. Kovelis D, Segretti NO, Probst VS, Lareau SC, Brunetto AF, Pitta F.
Validação do Modified Pulmonary Functional Status and Dyspnea Questionnaire e da
escala do Medical Research Council para o uso em pacientes com doença pulmonar
obstrutiva crônica no Brasil. J Bras Pneumol. 2008;34(12):1008-18. PMid:19180335.
http://dx.doi.org/10.1590/S1806-37132008001200005
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and by the distance covered during the 6MWT77. American Thoracic Society - ATS. American Thoracic Society statement:
guidelines for the six-minute walk test. Am J Respir Crit Care Med.
2002;166(1):111-7. PMid:12091180.
http://dx.doi.org/10.1164/ajrccm.166.1.at1102
http://dx.doi.org/10.1164/ajrccm.166.1.a...
. Patients were scored according to the results obtained in the four variables
(0-1 to BMI and 0-3 to FEV1, dyspnea and distance covered during the 6MWD)2828. Celli BR, Cote CG, Marin JM, Casanova C, Montes de Oca M, Mendez RA,
et al. The body-mass index, airflow obstruction, dyspnea, and exercise capacity index
in chronic obstructive pulmonary disease. N Engl J Med. 2004;350(10):1005-12.
PMid:14999112. http://dx.doi.org/10.1056/NEJMoa021322
http://dx.doi.org/10.1056/NEJMoa021322...
. The BODE index may be divided into quartiles: quartile 1 is the score of
0-2, quartile 2 is the score of 3-4, quartile 3 is the score of 5-6 and quartile 4 is
the score of 7-102828. Celli BR, Cote CG, Marin JM, Casanova C, Montes de Oca M, Mendez RA,
et al. The body-mass index, airflow obstruction, dyspnea, and exercise capacity index
in chronic obstructive pulmonary disease. N Engl J Med. 2004;350(10):1005-12.
PMid:14999112. http://dx.doi.org/10.1056/NEJMoa021322
http://dx.doi.org/10.1056/NEJMoa021322...
. The higher the score, the higher the probabilty of mortality of
patients2828. Celli BR, Cote CG, Marin JM, Casanova C, Montes de Oca M, Mendez RA,
et al. The body-mass index, airflow obstruction, dyspnea, and exercise capacity index
in chronic obstructive pulmonary disease. N Engl J Med. 2004;350(10):1005-12.
PMid:14999112. http://dx.doi.org/10.1056/NEJMoa021322
http://dx.doi.org/10.1056/NEJMoa021322...
.
Statistical analysis
To calculate the sample size, the authors considered that it would be necessary to have a correlation of r=0.80 between the performances of the tests, using as the null hypothesis a correlation below r=0.5, so that the value of r would be considered moderate - assuming an α error of 5% and β error of 20%2929. Browner WS, Cummings SR, Hulley SB. Estimando o tamanho da amostra e o poder estatístico: pontos básicos. In: Hulley SB, Cummings SR, Browner WS, Grady D, Hearst N, Newman TB. Delineando a pesquisa clínica: uma abordagem epidemiológica. 2ª ed. Porto Alegre: Artmed; 2003. p. 108-9.. According to these data, the sample size was calculated to be 29 subjects, corresponding to a statistical power of 80%.
The normality of the data was verified using the Shapiro-Wilk test. Data were expressed as a mean and standard deviation for normally distributed data and as a median (interquartile range) for data not normally distributed. The level of confidence was set at 5%.
The validity of the 6MST was verified using the concurrent and predictive validity
criteria. For concurrent validity, a Pearson correlation coefficient3030. Chaise FO, Candotti CT, Torre ML, Furlanetto TS, Pelinson PP, Loss
JF. Validation, repeatability and reproducibility of a noninvasive instrument for
measuring thoracic and lumbar curvature of the spine in the sagittal plane. Rev Bras
Fisioter. 2011;15(6):511-7. PMid:22045292.
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3131. Araujo VL, Carvalhais VO, Souza TR, Ocarino JM, Goncalves GG,
Fonseca ST. Validity and reliability of clinical tests for assessing passive ankle
stiffness. Rev Bras Fisioter. 2011;15(2):166-73. PMID: 21789368.
http://dx.doi.org/10.1590/S1413-35552011000200013
http://dx.doi.org/10.1590/S1413-35552011...
was conducted between the performances of the 6MWT and 6MST using the values
of T1 (first test) or T2 (second test) obtained in both tests. Correlations were also
conducted to verify the relationship between T1 on the 6MST with the better of the
two tests (T1 or T2) of the 6MWT. To verify the relationship between performances on
the 6MST and BODE index predictor of mortality, the Spearman correlation coefficient
was used. For the classification of this coefficient, a criterion of r>0.7 would
indicate that the instrument was valid3232. Terwee CB, Bot SDM, De Boer MR, Van der Windt DA, Knol DL, Dekker J,
et al. Quality criteria were proposed for measurement properties of health status
questionnaires. J Clin Epidemiol. 2007;60:34-42. PMid:17161752.
http://dx.doi.org/10.1016/j.jclinepi.2006.03.012
http://dx.doi.org/10.1016/j.jclinepi.200...
.
For the predictive validity criteria, ROC curves were constructed to verify the
sensitivity and specificity of the 6MST in classifying patients with COPD. The
cut-off point was determined from the highest sensitivity and specificity for the
best number of ascents on the step test of T1 or T2, and T1 only. Therefore, the area
under the curve was used as a criterion to determine the validity of the test. If the
test presented values below 0.7, they were considered to have low accuracy. Values
above 0.7 but below 0.9 would be considered to be accurate for some purposes. Lastly,
values over 0.9 would be considered highly accurate3333. Swets JA. Measuring the accuracy of diagnostic systems. Science.
1988;240:1283-93. http://dx.doi.org/10.1126/science.3287615
http://dx.doi.org/10.1126/science.328761...
. To verify whether the 6MST presented validity to classify patients with low
physical capacity, the 6MWT was used as the reference test with a cut-off of 334
m1515. Spruit MA, Polkey MI, Celli B, Edwards LD, Watkins ML, Pinto-Plata
V, et al. Predicting outcomes from 6-minute walk distance in chronic obstructive
pulmonary disease. J Am Med Dir Assoc. 2012;13(3):291-7. Pmid:21778120.
http://dx.doi.org/10.1016/j.jamda.2011.06.009
http://dx.doi.org/10.1016/j.jamda.2011.0...
. According to Spruit et al.1515. Spruit MA, Polkey MI, Celli B, Edwards LD, Watkins ML, Pinto-Plata
V, et al. Predicting outcomes from 6-minute walk distance in chronic obstructive
pulmonary disease. J Am Med Dir Assoc. 2012;13(3):291-7. Pmid:21778120.
http://dx.doi.org/10.1016/j.jamda.2011.06.009
http://dx.doi.org/10.1016/j.jamda.2011.0...
, the cut-off value of 334 m is a predictor of mortality, since patients with
COPD who had values below this cut-off died within a period of three years,
emphasizing the importance of this prognostic value.
Results
Thirty-four patients were initially included in the study, however two were excluded for not completing the assessment (abandoned the study). Of the 32 patients (24 male and eight female) included in the analysis, two had COPD grade I, nine grade II, 15 grade III and six stage IV2121. Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Pulmonary Disease - GOLD. 2012..
The sample characteristics are shown in Table 1. Table 2 shows the performance during the 6MWT and 6MST of the COPD patients evaluated.
Concurrent criterion validity
The performance values at T1 and T2, and at T1 or T2 during the 6MST showed a strong and positive correlation that was statistically significant with the 6MWT in all tests, and may be considered valid to verify the physical capacity of patients with COPD (Table 3, Figure 1). In addition, we found a significant negative weak correlation between performance on the 6MST and BODE index, and a significant weak correlation between performances in 6MST and FEV1. However, these correlations were insufficient to characterize validity (Table 3).
Relationship between performance on the 6MST and the 6MWT in patients with COPD. A = 6MST -T1 or T2 versus 6MWT -T1 or T2; B = 6MST -T1 versus 6MWT -T1 or T2. COPD = chronic obstructive pulmonary disease; 6MWT-T1 or T2 = Best performance on the first or second six-minute walk test; 6MST-T1= First six minute step test; 6MST-T1 or T2 = Best performance on the first or second six-minute step test.
Predictive criterion validity
The criterion validity of the 6MST to identify low physical capacity (compared to the 6MWT), using the number of the steps at T1 or T2 or only in T1, was considered accurate for some purposes, with the area under the curve of 0.8 (95% CI 0.62 to 0.98) and 0.85 (95% CI 0.70 to 0.99), respectively. For the number of steps in T1 or T2, the cut-off was set at 86 steps, with sensitivity of 90% and specificity of 64% (Figure 2). However, for the number of steps at T1, the cut-off was set at 78 steps, with 90% sensitivity and 68% specificity to classify patients with COPD (Figure 2).
Sensitivity and specificity of the 6MST in predicting physical capacity in COPD patients, using as reference the 6MWT - T1 or T2, with a cut-off point of 334 m. 6MWT = Six-minute walk test; 6MWT-T1 or T2 = Best performance on the first or second six-minute walk test; 6MST-T1 = First six-minute step test; 6MST-T1 or T2 = Best performance on the first or second six-minute step test.
ROC curves were not plotted for the BODE index nor the FEV1, since construct validity was not found.
Discussion
To the best of the authors knowledge, this is the first study performed to determine the predictive criterion validity of the 6MST to identify patients with low physical capacity and consequently poor prognosis in COPD. The number of steps in 6MST was valid in assessing exercise capacity in patients with COPD and could identify patients with low exercise tolerance and poor prognosis, so we suggest that this test may be used for this purpose.
The 6MST has shown to be clinically useful in estimating exercise tolerance in COPD3434. Marrara KT, Marino DM, Jamami M, Oliveira AD Jr, Di Lorenzo VAP.
Responsiveness of the six-minute step test to a physical training program in patients
with COPD. J Bras Pneumol. 2012;38(5):579-87. PMid:23147050.
http://dx.doi.org/10.1590/S1806-37132012000500007
http://dx.doi.org/10.1590/S1806-37132012...
, and requires minimal physical space and only two evaluators to perform the
test88. Dal Corso S, Duarte SR, Neder JA, Malaguti C, Fuccio MB, Castro
Pereira CA, et al. A step test to assess exercise-related oxygen desaturation in
interstitial lung disease. Eur Respir J. 2007;29(2):330-6. PMid:17050559.
http://dx.doi.org/10.1183/09031936.00094006
http://dx.doi.org/10.1183/09031936.00094...
,
1616. Neder JR, Nery LE. Fisiologia clínica do exercício. São Paulo: Artes
Médicas; 2003.. It is noteworthy that the 6MST, compared to 6MWT, uses specific muscle groups
(quadriceps). In addition, according to Swinburn et al.3535. Swinburn CR, Wakefield JM, Jones PW. Performance, ventilation, and
oxygen consumption in three different types of exercise test in patients with chronic
obstructive lung disease. Thorax. 1985;40(8):581-6. PMid:4035628 PMCid:PMC1020595.
http://dx.doi.org/10.1136/thx.40.8.581
http://dx.doi.org/10.1136/thx.40.8.581...
, the 6MST (to climb 15 steps/min at step height of 25 cm) provides greater
metabolic and ventilatory stress compared to exercises on a cycle ergometer and during
the 6MWT in patients with COPD. Thus, we suggest that the 6MST is a better test for
accessing the level of physical exertion in these patients.
Pessoa et al.3636. Pessoa BV, Jamami M, Basso RP, Regueiro EMG, Di Lorenzo VAP, Costa
D. Teste do degrau e teste da cadeira: comportamento das respostas
metábolo-ventilatórias e cardiovasculares na DPOC. Fisioter Mov. 2012;25(1):105-15.
http://dx.doi.org/10.1590/S0103-51502012000100011
http://dx.doi.org/10.1590/S0103-51502012...
concluded that the 6MST, the first two minutes of the 6MST, and the two minute
sit-to-stand test may be alternatives to assess the functional limitations of patients
with COPD, since they present similar metabolic, ventilatory, cardiovascular and dyspnea
responses.
The 6MWT is a test widely used to verify the physical capacity of patients with COPD.
Several studies have shown the relationship between the 6MWT and peak of oxygen
consumption (VO2) in the cardiopulmonary test which is considered a gold-standard
test1212. Cote CG, Pinto-Plata V, Kasprzyk K, Dordelly LJ, Celli BR. The 6-min
walk distance, peak oxygen uptake, and mortality in COPD. Chest. 2007;132(6):1778-85.
PMid:17925409. http://dx.doi.org/10.1378/chest.07-2050
http://dx.doi.org/10.1378/chest.07-2050...
,
3737. Bernstein ML, Despars JA, Singh NP, Avalos K, Stansbury DW, Light
RW. Reanalysis of the 12-minute walk in patients with chronic obstructive pulmonary
disease. Chest. 1994;105(1):163-7. PMid:8275726.
http://dx.doi.org/10.1378/chest.105.1.163
http://dx.doi.org/10.1378/chest.105.1.16...
38. Carter R, Holiday DB, Stocks J, Grothues C, Tiep B. Predicting
oxygen uptake for men and women with moderate to severe chronic obstructive pulmonary
disease. Arch Phys Med Rehabil. 2003;84(8):1158-64.
http://dx.doi.org/10.1016/S0003-9993(03)00047-9
http://dx.doi.org/10.1016/S0003-9993(03)...
39. Starobin D, Kramer MR, Yarmolovsky A, Bendayan D, Rosenberg I,
Sulkes J, et al. Assessment of functional capacity in patients with chronic
obstructive pulmonary disease: correlation between cardiopulmonary exercise, 6 minute
walk and 15 step exercise oximetry test. Isr Med Assoc J. 2006;8(7):460-3.
PMid:16889159.
40. Turner SE, Eastwood PR, Cecins NM, Hillman DR, Jenkins SC.
Physiologic responses to incremental and self-paced exercise in COPD: a comparison of
three tests. Chest. 2004;126(3):766-73. PMid:15364755.
http://dx.doi.org/10.1378/chest.126.3.766
http://dx.doi.org/10.1378/chest.126.3.76...
-
4141. Diaz O, Morales A, Osses R, Klaassen J, Lisboa C, Saldias F.
Six-minute-walk test and maximum exercise test in cycloergometer in chronic
obstructive pulmonary disease: are the physiological demands equivalent? Arch
Bronconeumol. 2010;46(6):294-301. http://dx.doi.org/10.1016/S1579-2129(10)70071-9
http://dx.doi.org/10.1016/S1579-2129(10)...
. Another study examined the relationship between the 6MWT and other tests, which
assessed different aspects of functional capacity, and found a relationship between the
distance traveled and sit-to-stand activity (r=0.67), static balance (r=0.52) and gait
velocity (r=-0.71)4242. Harada ND, Chiu V, Stewart AL. Mobility-related function in older
adults: assessment with a 6-minute walk test. Arch Phys Med Rehabil. 1999;80:837-41.
http://dx.doi.org/10.1016/S0003-9993(99)90236-8
http://dx.doi.org/10.1016/S0003-9993(99)...
. In addition, the 6MWT had its criterion validity determined and can be used to
predict mortality1212. Cote CG, Pinto-Plata V, Kasprzyk K, Dordelly LJ, Celli BR. The 6-min
walk distance, peak oxygen uptake, and mortality in COPD. Chest. 2007;132(6):1778-85.
PMid:17925409. http://dx.doi.org/10.1378/chest.07-2050
http://dx.doi.org/10.1378/chest.07-2050...
,
1313. Enfield K, Gammon S, Floyd J, Falt C, Patrie J, Platts-Mills TA, et
al. Six-minute walk distance in patients with severe end-stage COPD: association with
survival after inpatient pulmonary rehabilitation. J Cardiopulm Rehabil Prev.
2010;30(3):195-202. PMid:20040883 PMCid:PMC3047503.
http://dx.doi.org/10.1097/HCR.0b013e3181c565e4
http://dx.doi.org/10.1097/HCR.0b013e3181...
,
1515. Spruit MA, Polkey MI, Celli B, Edwards LD, Watkins ML, Pinto-Plata
V, et al. Predicting outcomes from 6-minute walk distance in chronic obstructive
pulmonary disease. J Am Med Dir Assoc. 2012;13(3):291-7. Pmid:21778120.
http://dx.doi.org/10.1016/j.jamda.2011.06.009
http://dx.doi.org/10.1016/j.jamda.2011.0...
,
4343. Budweiser S, Jörres RA, Pfeifer M. Treatment of respiratory failure
in COPD. Int J Chron Obstruct Pulmon Dis. 2008;3(4):605-18. PMid:19281077
PMCid:PMC2650592.. All these features favour the use of the 6MWT as a comparison test for the
construction validity of other functional tests.
Considering the concurrent criterion validity for the 6MST, we observed a significant and strong positive correlation (r=0.734) between the performances in the test and the 6MWT. The relationship between these two tests has been studied by Machado et al.2020. Machado NC, Natali V, Squassoni SD, Santana VT, Baldin AC, Fiss E. Estudo comparativo entre os resultados do teste de caminhada de seis minutos e do degrau de seis minutos em pacientes com doença pulmonar obstrutiva crônica. Arq Med ABC. 2008;32(Suppl. 2):S47-50. in 2008. These authors found no statistical difference between the physiological (HR and SpO2) and subjective (perceived exertion) variables studied and reported no correlation between the two tests; however, it is unclear if the performance in both tests was correlated. Note that, in the study, the height of the step was 14.5 cm, differing from the present study, in which the step used was 20 cm in height. Similarly, Schnaider and Karsten1919. Schnaider J, Karsten M. Testes de tolerância ao exercício em programa de fisioterapia hospitalar após exacerbação da doença pulmonar obstrutiva crônica. Fisioter Mov. 2006;19(4):119-26. observed that the number of steps on the 6MST with free cadence showed a good correlation (r=0.706; p<0.001) with the 6MWT in critical, hospitalized patients with COPD. However, it is worth mentioning that these authors used a step of 15 cm in height by 40 cm deep and 60 cm wide and conducted only one test. The present study is the first to verify that the 6MST compared to the 6MWT, using the methodological steps described earlier, can determine reduced functional capacity resulting from COPD. It also showed that the 6MST correlated with the BODE prognostic index and with the FEV1 - although the correlation was weak - suggesting that the performance at the 6MST can be considered a marker of the severity of the disease.
Similarly, other studies have shown that the BODE prognosis index was associated with
other methods of assessing functionality, such as the sit-to-stand in two minutes, the
6MWT performed on a treadmill4444. Regueiro EM, Di Lorenzo VA, Basso RP, Pessoa BV, Jamami M, Costa D.
Relationship of BODE Index to functional tests in chronic obstructive pulmonary
disease. Clinics. 2009;64(10):983-8. PMid:19841705 PMCid:PMC2763073.
http://dx.doi.org/10.1590/S1807-59322009001000008
http://dx.doi.org/10.1590/S1807-59322009...
, the level of physical activity in daily life4545. Mantoani LC, Hernandes NA, Guimaraes MM, Vitorasso RL, Probst VS,
Pitta F. Does the BODE index reflect the level of physical activity in daily life in
patients with COPD?. Rev Bras Fisioter. 2011;15(2):131-7. PMid:21789363.
http://dx.doi.org/10.1590/S1413-35552011000200008
http://dx.doi.org/10.1590/S1413-35552011...
and limitations in activities of daily living4646. Simon KM, Carpes MF, Correa KS, Dos Santos K, Karloh M, Mayer AF.
Relationship between daily living activities (ADL) limitation and the BODE index in
patients with chronic obstructive pulmonary disease. Rev Bras Fisioter. 2011;
15(3):212-8. PMid:21829985.
http://dx.doi.org/10.1590/S1413-35552011000300007
http://dx.doi.org/10.1590/S1413-35552011...
.
Predictive validity criterion was determined at T1 or T2, or solely at T1, with the
6MST, using the 6MWT as the gold-standard to classify individuals with COPD concerning
their physical capacity. For both comparisons, the 6MST was shown to be accurate for
some purposes according to the classification of Swets3333. Swets JA. Measuring the accuracy of diagnostic systems. Science.
1988;240:1283-93. http://dx.doi.org/10.1126/science.3287615
http://dx.doi.org/10.1126/science.328761...
. This result suggests that the use of this test as a criterion for indication
for surgical interventions, a lung transplant for example, should be avoided and new
studies should be conducted to check whether it is appropriate for this purpose.
The fact that T1 presented concurrent and predictive criterion validity suggests that there is no need for a familiarization test. It also indicates that it might be interesting to evaluate the test on a larger sample. Based on the cut-off of 78 steps, patients with similar or lower values can be classified as having a low physical capacity, suggesting the need for physical therapy intervention. However, it is important to consider that the present study had a lower than ideal sample to verify criterion validity, suggesting the need of future studies.
Study limitations
The present study had the following limitations. It was not designed to verify predictive validity, since a larger sample size would be needed for this type of analysis. However, it should be emphasised that the study raised the hypothesis of a relationship between the 6MST and the prognosis of patients with COPD, which should be addressed in future studies.
Conclusion
The performance observed on the 6MST was valid for determining low physical capacity in patients with COPD with a cut-off of 78 steps, whereas values below that represented patients having a poorer prognosis.
Acknowledgements
To all colleagues from the Laboratory of Spirometry and Respiratory Physical Therapy for the collaboration as well as to the participants in the study. We also acknowledge the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Process: 508310/2010-5) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil, for financial support.
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Publication Dates
-
Publication in this collection
May-Jun 2014
History
-
Received
13 May 2013 -
Reviewed
13 Aug 2013 -
Accepted
11 Nov 2013