Reanalysis of the 12-Minute Walk in Patients With Chronic Obstructive Pulmonary Disease – Data Analysis

May-8-2014

Results of the walking distances in each interv al and the cumulative Borg scores were compared by means of analysis of variance. Where statistical significance was achieved with the F test (p < 0.05), the least significant difference between the means was calculated. The relationship between the distance walked and the spirometric measurements or the measurements obtained from the symptom-limited maximal exercise tests were analyzed using simple linear regression. Multiple linear regression was used to determine the relationship between the independent variable of Vo max and the dependent variables of walking distance and Borg score. Values of probability less than 0.05 were considered statistically significant. All experimental values are reported as mean ± SD where applicable.
We analyzed the changes in the different test results from session to session by calculating the percentage change in each test from the initial measurement on that patient. Thus, there were five data points for each of the nine subjects, yielding a total of 45 points for analysis by simple linear regression.
The demographics of our patients are shown in Table 1. Nine male patients with a mean age of 67 years took part in the study. The average patient had moderate COPD, as evidenced by the FEVj of 1.32 ± 0.28 L. The mean maximal workload achieved in the exercise test was 81 W, which can be compared with the predicted workload of 180 W for men over 60 years of age/’ The Vo.,max was slightlv over a liter.
The 12-min walking distance was reduced to a mean of 2,650 ft. Three of our patients consistently reached an anaerobic threshold as determined from expired gas analysis during the exercise tests, while the remaining 6 patients usually did not reach an anaerobic threshold. sildenafil citrate pink

The walking distances in each 2-min interval of the 12-min walk were very similar (Fig 1). None of the distances differed significantly (p > 0.05) from the others. However, the distance walked in the first 2 min was slightly higher than the distances walked in the other 5 intervals.
In contrast, the Borg scores became progressively higher (Fig 2) as the walking time increased. The least significant difference between Borg scores was 1.4 by means of analysis of variance, and accordingly many of the Borg scores differed significantly. This demonstrates that the duration as well as the intensity of the exercise influences the Borg score.
There were highly significant correlations between the different walking intervals (Table 2). All of the correlation coefficients are above 0.90 (p < 0.001) except that between the first 2 min (0 to 2) and the last 2 min (10 to 12), which is 0.85. Note the verv high correlations between the 4- and 6-min walks, the 4-and 12-min walks, and the 6- and 12-min walks.
The functional capacity of the patients as assessed by the symptom-limited maximal exercise test was significantly correlated with the functional capacity as assessed bv the 12-min walk (Table 3). A higher correlation was found when the Vo,max and the Vo, max were normalized by dividing by the weight of the patient. Also, the correlation coefficients between the distance walked and the Vo,max were greater than those between distance walked and the Vo,max.

Table 1—Demographics of an All-Male Patient Population (No = 9)

Clinical Factors Mean ± SD
Age, yr 67 ±4
FEVj, L 1.32 ±0.28
FVC, L 3.40 ±0.61
Work Load, W 81 ±32
Vo2max, ml/min 1,103 ± 129
Vco2max, ml/min 1,228 ±220
Maximal minute ventilation, L/min 46.0±6.4
12-min walk, FT 2,650 ±350

Table 2—Correlation Coefficients Between Different Walking Distances

Walking Distances/min Correlation Coefficient
Walk 0 to 2 and walk 2 to 4 0.92
Walk 0 to 2 and walk 10 to 12 0.85
Walk 0 to 2 and walk 0 to 4 0.98
Walk 0 to 2 and walk 0 to 6 0.95
Walk 0 to 2 and walk 0 to 12 0.94
Walk 0 to 4 and walk 0 to 6 0.98
Walk 0 to 4 and walk 0 to 12 0.98
Walk 0 to 6 and walk 0 to 12 0.97

Table 3—Correlation Coefficients Between Vot and Vco2 and Various Walking Distances

WalkingDistances Vo2 VoAg Vco2 VcOa/kg FEV, FEV,/kg FVC FVC/kg
0 to 2 min 0.45 0.55 0.35 0.39 0.08 0.13 -0.04 0.09
2 to 4 min 0.49 0.68 0.36 0.48 0.17 0.26 -0.12 0.12
4 to 6 min 0.46 0.68 0.38 0.52 0.17 0.29 -0.28 0.03
6 to 8 min 0.48 0.71 0.41 0.56 0.13 0.26 -0.18 0.12
8 to 10 min 0.49 0.66 0.41 0.51 0.14 0.23 0.11 0.13
10 to 12 min 0.49 0.69 0.40 0.58 0.17 0.34 -0.15 0.22
0 to 4 min 0.48 0.62 0.36 0.44 0.12 0.19 -0.08 0.11
0 to 6 min 0.51 0.67 0.40 0.48 0.18 0.24 -0.17 0.05
0 to 12 min 0.49 0.65 0.38 0.53 0.15 0.26 -0.16 0.12

Figure-1

Figure 1. Mean distances walked during each 2-min interval of the 12-min walk.

Figure-2

Figure 2. Mean Borg scores at the end of each 2-min during the 12-min walk.