Reanalysis of the 12-Minute Walk in Patients With Chronic Obstructive Pulmonary Disease – Materials and Methods
The 12-min walking test has become a popular method by which one may determine the functional capacity of an individual with COPD. Cooper originally designed the 12-min running test as a means to correlate fitness with maximal oxygen intake (Vo2max) in healthy young men. McGavin et al2 adapted this idea in developing a walking test as a simple method to estimate exercise tolerance in patients with chronic bronchitis. Recently, several reports suggested that the same information can be obtained with tests of shorter duration.
The objectives of this study were (1) to determine the correlation between the different intervals in the 12-min walking test to assess if it is necessary to walk the patient for 12 full minutes; (2) to determine which of the intervals best correlated with Vo2max and maximal CO£ expelled (Vo2max); (3) to determine if adding a measure of effort (ie, the Borg score) improves the correlations; and (4) to determine the degree of correlation between changes in the Vo2max and changes in the walking test or spirometry.
The subjects in the study were recruited from the Outpatient Pulmonary Clinic at the Veterans Administration Medical Center, Long Beach, Cal, to participate in a study to evaluate the effects of buspirone on anxiety and exercise in COPD patients, which has been previously reported. The patients agreed to take part in the study and signed informed consent forms approved by the Institutional Review Board at this institution. Since the results of that study showed no significant changes while patients were taking buspirone compared with placebo, we elected to combine the data to study the 12-min walk in more depth. canadian neightbor pharmacy
Inclusion and exclusion criteria for this study were therefore identical to the guidelines used by Singh et al. Inclusion criteria included a FEVj below 1.4 L, a ratio of FEV, to forced vital capacity (FVC) below 0.50, exercise limited by dyspnea, and a stable disease state. Patients were required to be between 40 and 75 years of age, and they continued to receive regular medications throughout the study. Exclusion criteria included known left ventricular disease or neuromuscular or other medical problems which would preclude them from walking for 12-min or performing cycle ergometry.
Each patient was seen 6 times, at 0, 3, 6, 8, 11 and 14 weeks. Each visit included spirometry (Vitalograph rolling seal spirometer) followed by a symptom-limited maximal exercise test and the 12-min walk. For the exercise test, the work load was increased 5 to 15 W/min on a bicycle ergometer (Gould Godard), while a metabolic cart (Sensormedics MMC Horizon System 4400 metabolic cart) measured the oxygen consumption (Vo2), the C02 expelled (Vo2), and the minute ventilation at each 30-s interval. For the 12-min walk, patients walked in an air-conditioned corridor that was marked off in 20-ft intervals. Subjects were told to go as far as they could in 12 min, but to pace themselves so that they would not have to stop. To eliminate learning effects, patients performed three practice walks prior to beginning the study, as suggested by Swinbum et al. The participants were under constant observation, but the nurse or technician did not walk with the patient. At the end of each 2 min the breathlessness of the patient was assessed with the modified Borg scale (upper limit of 10). The distance that the patient walked in each 2-min interval was recorded.