Interpreting small differences in functional status: the Six Minute Walk test in chronic lung disease patients.

Functional status measurements are often difficult to interpret because small differences may be statistically significant but not clinically significant. How much does the Six Minute Walk test (6MW) need to differ to signify a noticeable difference in walking ability for patients with chronic obstructive pulmonary disease (COPD)? We studied individuals with stable COPD (n = 112, mean age = 67 yr, mean FEV1 = 975 ml) and estimated the smallest difference in 6MW distances that was associated with a noticeable difference in patients' subjective comparison ratings of their walking ability. We found that the 6MW was significantly correlated with patients' ratings of their walking ability relative to other patients (r = 0.59, 95% confidence interval [CI]: 0.54 to 0.63). Distances needed to differ by 54 m for the average patient to stop rating themselves as "about the same" and start rating themselves as either "a little bit better" or "a little bit worse" (95% CI: 37 to 71 m). We suggest that differences in functional status can be statistically significant but below the threshold at which patients notice a difference in themselves relative to others; an awareness of the smallest difference in walking distance that is noticeable to patients may help clinicians interpret the effectiveness of symptomatic treatments for COPD.

[1]  G H Guyatt,et al.  How should we measure function in patients with chronic heart and lung disease? , 1985, Journal of chronic diseases.

[2]  P. Tugwell,et al.  Minimum important difference between patients with rheumatoid arthritis: the patient's perspective. , 1993, The Journal of rheumatology.

[3]  R. Hainsworth,et al.  Assessment of respiratory function in patients with chronic obstructive airways disease. , 1979, Thorax.

[4]  Twelve-minute walking test in a group of Dutch patients with chronic obstructive pulmonary diseases; relationship with functional capacity. , 1986, European journal of respiratory diseases. Supplement.

[5]  D. Redelmeier,et al.  Medical decision making in situations that offer multiple alternatives. , 1995, JAMA.

[6]  W. F. Miller,et al.  Chronic obstructive airway diseases. Current concepts in diagnosis and comprehensive care. , 1975, JAMA.

[7]  G. Guyatt,et al.  Randomised controlled trial of respiratory rehabilitation , 1994, The Lancet.

[8]  J. Bugler,et al.  Effect of arterial oxygen desaturation on six minute walk distance, perceived effort, and perceived breathlessness in patients with airflow limitation. , 1993, Thorax.

[9]  D. Redelmeier,et al.  Spirometry and dyspnea in patients with COPD. When small differences mean little. , 1996, Chest.

[10]  H. D. Short,et al.  Bronchodilators in chronic air-flow limitation. Effects on airway function, exercise capacity, and quality of life. , 1987, The American review of respiratory disease.

[11]  C. Ranawat,et al.  A self-administered hip-rating questionnaire for the assessment of outcome after total hip replacement. , 1992, The Journal of bone and joint surgery. American volume.

[12]  D. Redelmeier,et al.  Assessing the clinical importance of symptomatic improvements. An illustration in rheumatology. , 1993, Archives of internal medicine.

[13]  A. Woodcock,et al.  Two-, six-, and 12-minute walking tests in respiratory disease. , 1982, British medical journal.

[14]  G. Guyatt,et al.  The 6-minute walk: a new measure of exercise capacity in patients with chronic heart failure. , 1985, Canadian Medical Association journal.

[15]  William J. Rogers,et al.  Prediction of Mortality and Morbidity With a 6-Minute Walk Test in Patients With Left Ventricular Dysfunction , 1993 .

[16]  R. Doll,et al.  The Epidemiology of Cancer , 1980, Cancer.

[17]  M. Artvinli,et al.  Dyspnoea, disability, and distance walked: comparison of estimates of exercise performance in respiratory disease. , 1978, British medical journal.

[18]  G. Guyatt,et al.  Assessing the minimal important difference in symptoms: a comparison of two techniques. , 1996, Journal of clinical epidemiology.

[19]  J. Martin,et al.  Effect of nutritional status on exercise performance in patients with chronic obstructive pulmonary disease. , 1989, The American review of respiratory disease.

[20]  G H Guyatt,et al.  Effect of encouragement on walking test performance. , 1984, Thorax.

[21]  G. Guyatt,et al.  On the debate over methods for estimating the clinically important difference. , 1996, Journal of clinical epidemiology.

[22]  G. Guyatt,et al.  Long-term outcome after respiratory rehabilitation. , 1987, CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne.

[23]  Reproducibility of walking test results in chronic obstructive airways disease. , 1988 .

[24]  Gordon Guyatt,et al.  Measuring Health-Related Quality of Life , 1993, Annals of Internal Medicine.

[25]  S. P. Gupta,et al.  Twelve-minute walking test for assessing disability in chronic bronchitis. , 1976, British medical journal.

[26]  D A Redelmeier,et al.  Discrepancy between medical decisions for individual patients and for groups. , 1990, The New England journal of medicine.