Reanalysis of the 12-Minute Walk in Patients With Chronic Obstructive Pulmonary Disease – Results
The correlations are similar for all of the different walking distances except for the first 2-min distance, which correlates less well than the others. None of the walking distances was closely correlated with either the FEV, or the FVC.
The 6-niin and 12-min walking distances are more closely correlated with the Vo., than were the FEV, or FVC (Table 4). However, the FEV, is better correlated with the Vco, than are the walking distances. The negative correlation between the FVC and the Vo,/kg and the Vco,/kg demonstrates that the FEV, is much more important than the FVC in determining exercise capacity in patients with moderate obstructive disease. The v alues in the last rows of the table, labeled “12 min + Borg” and “6 min + Borg,” represent the multiple correlation coefficients when the 12- and 6-min walking distances and the Borg scores at the end of the walks were used as the independent variables in multiple regression analysis. The purpose of evaluating this is to determine if including a measure of ef fort (the Borg score) improves the correlations. The analysis shows that there is very little increase in the correlation coefficients when the Borg score was included. When other measures of the Borg score were used in multiple regression, there was likewise no increase in the correlation. my canadian pharmacy.com
When changes in the walking distances were correlated with changes in the Vo,max and Vo,max, it was found (Table 5) that there was a closer correlation with the 12-min test than with the 6-min test or any others (compare 0.72 with 0.64 and 0.59 with 0.49), suggesting that it is advantageous to do the walking test for 12 min when changes in an individual’s exercise capabilities are being assessed. As expected, there was a relatively close correlation between the percentage changes in Vo., and Vco., (r = 0.80), as well as a close correlation between changes in the 6- and 12-min walking distances (r = 0.84). Percentage changes in Vo,max and Vco max were comparably correlated with the percentage changes in the 6-min walk and the FEV,. The mean maximal absolute changes for the 11 patients during the 14-week study period were as follows: FEV, = 35.8 ± 13.5 percent; 6-min walk = 10.3 ± 5.6 percent; 12-min walk = 9.3 ± 2.7 percent; Vo2= 25.7 ± 14.5 percent; and Vco., = 26.7 ± 11.9 percent.
Our results show that the distances walked in each 2-min interval of the 12-min walk are very consistent (Fig 1), in contrast to the Borg scores which tend to get progressively higher (Fig 2) as the patient walks for a longer period of time. Significantly, the changes which occur in the results of the maximal exercise test between testing sessions correlate better with changes in the 12-min walking distance test than with changes in shorter walking distance tests.
Cooper used a 12-min running test to evaluate fitness in healthy young men. McGavin et al2 adapted this test to ev aluate exercise tolerance in patients with COPD. They proposed that patients perform a 12-min walking test in which the distance traveled was measured and the results were compared to other measures of respiratory ability. The authors concluded that this test was a clinically useful tool because it is objective in nature and allows patients to be placed on a continuous scale of performance. Other studies have focused on evaluating patients on the basis of shorter walking distances.
Table 4—Correlation Coefficients Between Votmax and Vcotmax and 6- and 12-min Walking Distance, With and Without Borg Scores Included, and Spirometry
|6 min ± Borg||0.54||0.67||0.40||0.56|
|12 min ± Borg||0.55||0.69||0.40||0.57|
Table 5—Correlation Coefficients Between Changes in Vo2max and Vcot and Changes in the Various Walking Distances