The effect of cigarette smoking status on six-minute walk distance in patients with intermittent claudication

The purposes of the study were threefold: (1) to compare 6-minute walk performance as a measure of exercise tolerance among three different groups of peripheral arterial occlusive disease (PAOD) patients with intermittent claudication-current smokers, former smokers, and patients who have never smoked; (2) to identify important covariates that might affect the relationship between smoking and exercise in the PAOD population; (3) to determine whether differences among the three groups in 6-minute walk performance persist after statistically controlling for the significant covariates. Recruited into the study were 415 PAOD patients with intermittent claudication between the ages of 42 and 88 years. The self-reported smoking status consisted of 182 current smokers, 196 former smokers, and 37 patients who had never smoked. The authors recorded 6-minute walk distance, a reliable measurement of exercise tolerance in PAOD patients, as well as age, body composition, self-reported ambulatory function, self-reported physical activity, and standard peripheral hemodynamics. Nonsmokers walked significantly farther (413 +/- 14 m; mean +/- standard error) and took more steps (665 +/- 14 steps) than either current (352 +/- 7 m; 563 +/- 9 steps) or former smokers 370 +/- 7 m; 600 +/- 8 steps) (p<0.05). The nonsmokers had a higher ankle-brachial index (ABI) value (0.70 +/- 0.03) than patients who actively smoked 0.62 +/- 0.01 (p<0.03); the authors observed an inverse relationship between smoking history and self-reported physical activity (WIQ Distance Score: nonsmokers 51 +/- 6%, former smokers 38 +/- 3%, and smokers 32 +/- 2%) (p<0.01). From a multivariate perspective, ABI, physical activity, and perceived walking ability were the only independent predictors of 6-minute walk distance. Differences in the adjusted 6-minute walk distance among the nonsmokers (388 +/- 13 m), current smokers (359 +/- 6 m), and former smokers (368 +/-6 m) no longer remained after controlling statistically for these covariates. The findings suggest that 6-minute walk distance is a sensitive measure to detect differences in submaximal exercise performance between smoking and nonsmoking PAOD patients with intermittent claudication. Moreover, the group difference in the 6-minute walk distance is explained by group differences in walking perception, PAOD severity, and physical activity level.