Six minutes walk test: study of the effect of learning in chronic obstructive pulmonary disease patients

Abstracts

INTRODUÇÃO: Testes de caminhada de seis minutos vêm sendo utilizados de forma crescente para avaliar a efetividade de diferentes opções terapêuticas clínicas e cirúrgicas em pneumopatias. Entretanto, a falta de padronização para a sua realização pode influenciar as aferições, prejudicando a qualidade da avaliação. Nesse sentido, formulamos a hipótese de que os pacientes têm melhor performance com a realização do teste de caminhada de seis minutos após aprendizado. OBJETIVO: Determinar o possível efeito do aprendizado na distância percorrida durante o teste de caminhada de seis minutos em portadores de doença pulmonar obstrutiva crônica. MÉTODO: Foram analisados, retrospectivamente, 35 prontuários de pacientes portadores de doença pulmonar obstrutiva crônica, encaminhados ao Programa de Reabilitação Pulmonar do Hospital Universitário de Brasília, e que tivessem realizado, em dias alternados, dois testes de caminhada de seis minutos, espirometria e gasometria arterial. O diagnóstico clínico e funcional de doença foi baseado na história de exposição a fator de risco, produção de secreção, dispnéia e prova espirométrica alterada, após o uso de broncodilatador. RESULTADOS: Observamos que as distâncias percorridas no segundo teste de caminhada de seis minutos (515 ± 82 metros) foram maiores que as distâncias percorridas no primeiro (480 ± 85 metros), com valores estatisticamente significativos (p < 0,05). Entretanto, as variáveis esforço muscular, percepção da dispnéia (escala de Borg), saturação periférica da hemoglobina pelo oxigênio, freqüência respiratória e freqüência cardíaca não apresentaram diferença significativa entre os dois testes (p<0,05). CONCLUSÃO: O presente estudo sugere a necessidade de padronização do teste de caminhada de seis minutos, com a realização de pelo menos dois testes para se avaliar a capacidade funcional de pacientes portadores de doença pulmonar obstrutiva crônica.

Caminhada; Efetividade; Pneumopatias obstrutivas

ORIGINAL ARTICLE

Six minutes walk test: study of the effect of learning in chronic obstructive pulmonary disease patients^*

Sérgio Leite Rodrigues; Hélder Fonseca e Mendes; Carlos Alberto de Assis Viegas ^(TE-SBPT)

^{Correspondence}

ABSTRACT

BACKGROUND: The six minutes walk test has been increasingly utilized to assess the effectiveness of different clinical and surgical treatment options in pulmonary diseases. However lack of standardization for their performance may influence measurements and jeopardize assessment of the functional capacity of patients with cardiopulmonary disease.

OBJECTIVE: To determine the possible effects of learning on the distance covered during the six minute walk test for bearers of chronic obstructive pulmonary disease.

METHOD: A retrospective analysis of 35 medical records of COPD patients referred to the Pulmonary Rehabilitation Program of the University Hospital of BrasÌlia was carried out. On alternate days these patients had performed two six minutes walk tests, spirometry and arterial blood gas analysis. Clinical and functional diagnosis was based upon the history of exposure to risk factors, mucus production, dyspnea and spirometric dysfunction after use of bronchodilators. The Student test was used for the comparison of results that were different.

RESULTS: The distances covered in the second six-minute walk test (515 ± 82 meters) were greater than those covered in the first six-minute walk test (480 ± 85 metros), with statistically significant differences (p<0.05). However measurements of the muscular effort and perception of dyspnea (Borg scale), peripheral blood oxygen saturation (SpO2), respiratory and heart rates did not disclose any statistically significant differences between the two tests (p<0.05).

CONCLUSION: The present study suggests that in order to standardize the six minutes walk test, the procedure should be performed at least twice to better assess the functional capacity of patients, bearers of chronic obstructive pulmonary disease.

Key words: Walking. Effectiveness. Lung diseases, obstrutive.

Abbreviations used in this paper:

TLC – Total lung capacity

FVC – Forced vital capacity

COPD – Chronic obstructive pulmonary disease

BMI – Body mass index

PaCO₂ – Arterial carbon dioxide tension

PaO₂ – Arterial oxygen tension

SpO₂ – Arterial oxygen saturation by pulse oximetry

6MWT – 6-minute walk test

FEV₁ – Forced expiratory volume in one second

FEV₁/FVC – Ratio of forced expiratory volume in one second to forced vital capacity

Introduction

The 12-minute run was initially standardized by Cooper⁽¹⁾ in order to evaluate the physical capacity of healthy individuals and was later modified into the 12-minute walk in order to evaluate the physical capacity of patients with chronic bronchitis.⁽²⁾ Subsequently, Butland et al. successfully explored the use of 2-, 6-, and 12-minute walk tests in the evaluation of the physical capacity of patients with chronic obstructive pulmonary disease (COPD).⁽³⁾ Since then, walk tests have been more frequently used to evaluate the efficacy of various clinical and surgical treatment modalities.⁽⁴⁾

It is well known that COPD may lead to physical impairment, resulting in physical and social limitations that affect the quality of life of those suffering from COPD.⁽⁴⁾ In the evaluation of physical capacity, the 6-minute walk test (6MWT) also helps evaluate functional capacity and the ability to perform daily physical activities. This assessment has proven important in the dynamic evaluation and clinical management of those severe chronic cardiopulmonary disease patients for whom traditional (maximal workload) cardiopulmonary exercise testing is inadvisable.^(4,5)

In Brazil, guidelines for pulmonary function testing set forth by the First Brazilian Consensus on COPD and the Sociedade Brasileira de Pneumologia e Tisiologia (SBPT; Brazilian Society of Pulmonology and Phthisiology) recommend neither performing nor standardizing 6MWTs in the evaluation of patients with COPD.^(6,7) The American Thoracic Society (ATS) has recently issued new guidelines suggesting that submitting patients to a pre-test 6MWT trial can improve motor coordination and reduce patient anxiety in subsequent tests. Such “practice runs” may improve the reliability of final test results, reducing the effect of the neuromuscular and psychological factors that are characteristic of COPD patients.^(8-10)

Since there is lack of consensus and very few Brazilian studies have been published on this subject, the objective of the present study was to determine the effect of pre-test practice on the total distance covered in the 6MWT by the COPD patients treated at our hospital.

Methods

This study involved retrospective analysis of the medical records of patients referred to the Hospital Universitário de Brasília Pulmonary Rehabilitation Program from October 2002 to May 2003.

The results of spirometric and blood gas analysis, as well as those from the first and second 6MWTs, were compiled from the selected medical records and subsequently evaluated.

Both the first and the second 6MWTs were carried out according to the ATS guidelines.⁽⁹⁾ Patients performed tests on alternating days. The objective of the first test was to determine the total distance covered without the training effect. The objective of the second test was to check the performance and relate it to the potential effect of training and adaptation to the test. Pre-test and post-test values for respiratory rate, heart rate, arterial oxygen saturation by pulse oximetry (SpO₂), perceived degree of muscle effort and dyspnea according to the modified Borg scale,⁽¹¹⁾ and total distance covered were determined. The equations proposed by Enright and Sherrill⁽¹²⁾ were used in evaluating the normality of data in the results for total distance covered.

For both the first and second 6MWTs, pre- and post-test SpO₂ was measured with a pulse oximeter (model 920M, Healthdyne Technologies^®, Marietta, GA, USA). The oximeter was affixed to the waist of the patient, and the sensor was attached to the index finger of the dominant arm.

Spirometry was performed with a Vmax–22 series spirometer (SensorMedics, Yorba Linda, CA, USA). With the patient seated, 3 forced expiration maneuvers were performed according to the criteria for acceptability and reproducibility recommended by the ATS.⁽¹³⁾ Forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), and FEV₁/FVC ratio (%) were determined. Absolute values and percentage of predicted values for gender, age, and height were determined using the table devised by Knudson et al.⁽¹⁴⁾

After local anesthesia with xylocaine was administered, a 2-mL blood sample was taken from each individual for use in the arterial blood gas analysis. With the individual at rest, blood was drawn from the radial artery of the nondominant arm. Immediately after collection, the blood samples were processed in a computerized, automated blood gas analyzer for determination of PaO₂ and PaCO₂ (expressed in mmHg), as well as SpO₂ (expressed as percentage of saturation). The apparatus used was a model 278 Gas System^® analyzer (Ciba-Corning, Diagnostics Corp; Medfield, MA, USA) and was calibrated every morning prior to the beginning of tests.

Medical records of patients with COPD, referred to the Pulmonary Rehabilitation Program of the Hospital Universitário de Brasília, were included in the study if they documented the performance of 2 consecutive 6MWTs, spirometry, and blood gas analysis. The clinical and functional diagnosis of COPD was based on patient history of exposure to risk factors, as well as on mucus production, dyspnea and alterations in spirometry parameters after administration of bronchodilators.⁽¹⁵⁾

Records of patients who, for any reason, failed to complete the 2 6MWTs, or who were not submitted to spirometry and blood gas analysis, were not included in the study.

Results are expressed as means and standard deviations. Results from both tests were compared using Student’s t-test. Values of p < 0.05 were considered statistically significant.

Results

In this study, 38 patient records were initially selected. However, 3 were excluded because of a lack of test documentation. Therefore, the medical records of 35 patients (28 males and 7 females) were studied. Mean age was 65 ± 8 (range, 46 to 81). Mean body mass index (BMI) was 24 ± 4 kg/m² (range, 15 to 31 kg/m²). Mean FEV₁ was 62 ± 24% of predicted value (range, 38 to 86%), mean FVC was 95 ± 25% of predicted value (range, 46 to 120%), and mean FEV₁/FVC ratio was 52 ± 14% (range, 24 to 66%). Mean pH value in blood gas analysis was 7.4 ± 0, mean PaO₂ was 74 ± 9 mmHg (range, 65 to 83 mmHg), and mean PaCO₂ was 37 ± 11 mmHg (range, 26 to 48 mmHg) (Table 1).

There were no statistically significant differences between the first 6MWT and the second 6MWT in the values found for perceived degree of muscle effort and dyspnea (modified Borg scale), SpO₂, respiratory rate or heart rate. The mean distance covered in the first 6MWT was 480 ± 85 m (range, 277 to 616 m), compared with 515 ± 82 m (range, 280 to 640 m) in the second 6MWT. The difference between these values was found to be statistically significant (Table 2).

Discussion

Pulmonary rehabilitation has proven to be efficacious in improving functional capacity and muscle strength in COPD patients, even though results of pulmonary function tests may not improve.^(16,17) The 6MWT is frequently used in the evaluation of physical capacity and evolution in patients with COPD.⁽⁹⁾ Solway et al.⁽⁵⁾ state that 87% of pulmonary rehabilitation programs in the USA and Canada use 6MWTs due to the simplicity, low cost, and good correlation with submaximal physical working capacity afforded by the test. According to Rodrigues et al.,⁽¹⁸⁾ 6MWT results positively and significantly correlate with COPD prognostic indicators such as PaO₂ and FEV₁.

In studies of the 6MWT, the effect of training (or “learning”) is mentioned as an interference factor in the results and reproducibility of the test.^(8-10) However, there is no consensus regarding the utility of administering practice tests in the assessment of functional capacity in patients diagnosed with COPD. In a recent study evaluating 6MWT results in a pulmonary rehabilitation program, Moreira et al.⁽¹⁹⁾ highlighted the importance of 6MWT standardization. The authors suggested that the main factors involved in increasing physical performance on the 6MWT are verbal encouragement given by the examiner and proper patient guidance during the test. However, in the cases reviewed in our study, identical phrases of encouragement and guidance were used during both tests, and we observed a significant difference (p < 0.05) between the results from first 6MWT and those from the second 6MWT. Knox et al.⁽⁴⁾ reported a 33% increase in the distance covered in repeated tests, in which the verbal stimulation did not vary. In that study, the authors submitted patients to 12 6MWTs on 3 consecutive days and observed that, by the third test, distances covered had increased by 16%. In the cases we studied, only 2 tests were administered, and we observed a mean increase of 8%, constituting a statistically significant difference between the distances covered. This suggests that patients adapted to the practical aspects of the test, such as anxiety control and recognition of the limits of the test, as well as adapting neuromuscularly to the activity to be performed. In a metaanalysis, Lacasse et al.⁽²⁰⁾ related significant clinical improvement in patients undergoing pulmonary rehabilitation to an increase in distance covered in the 6MWT of approximately 50 m (range, 27.8 to 92.8 m). In our study, there was a mean increase of 35 m in distance covered between the first and second 6MWTs, which is in accordance with the literature.^(20,21) We believe that the statistical difference between the first and the second 6MWTs found in the cases reviewed in our study justifies the administration of the first (training) 6MWT. If this “training effect” were not taken into account, the effects of therapeutic interventions would be overestimated in relation to the functional capacity of patients, especially in those patients with more advanced disease.

Noseda et al.,⁽²¹⁾ in a study on the reproducibility of physical tests for COPD patients, stated that the training effect over short time periods with repetition of the 6MWT is often relevant, even without verbal stimulation. The authors reported a mean increase of 24.5 m after 3 repetitions of the test in 3 consecutive months without the use of verbal stimulation. According to Redelmeier et al.,⁽¹⁰⁾ the performance of 6MWTs on consecutive days is sufficient to counteract any possible effects of training. These authors suggest that a plateau is reached after 2 tests, and that there is no statistically significant difference between those 2 tests and tests performed later.

As for distance covered, the results from the first and second 6MWTs evaluated in our study are in agreement with the reference values for healthy individuals suggested by Enright et al.¹² However, in the cases we studied, phrases of encouragement were used at one-minute intervals during both tests, which may explain the better physical performance of the patients in our study when compared to those studied by those authors.

There were no significant differences in respiratory rates, heart rates or perceived degree of muscle and respiratory effort (Borg scale) between the first and second 6MWTs (p > 0.05). This suggests that the degree of effort made by the patients was similar in both tests, reaffirming the hypothesis that the determinant factor for the significant increase seen in the second 6MWT was the training effect.

The lack of standardization of the 6MWT, which may influence test results and preclude comparisons among results from various studies, is an issue which we must put into a national context.^(16-19)

In conclusion, within the population studied, there was a statistically significant difference in test results between the first and second 6MWTs. We believe that administration of more than one 6MWT should be considered during the process of functional evaluation of patients with chronic lung disease. This practice may provide higher quality results and give examiners greater confidence in their assessment of the physical capacity of patients with COPD, as well as in their evaluation of therapeutic outcomes.

References

Submitted: 12 June 2003.

Accepted, after revision: 20 November 2003.

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*

Study carried out in the Laboratório de Reabilitação Pulmonar do Serviço de Pneumologia of the Hospital Universitário de Brasília da Faculdade de Medicina da Universidade de Brasília (UnB).

Publication Dates

• Publication in this collection
  08 June 2004
• Date of issue
  Apr 2004

History

• Accepted
  20 Nov 2003
• Received
  12 June 2003