ABC | Volume 114, Nº3, March 2020

Original Article Farah et al. Effort during 6-minute walk test Arq Bras Cardiol. 2020; 114(3):486-492 Figure 1 – Study design. Clinical examination Medical history Anthropometry Ankle brachial index Graded treadmill test Ventilatory thereshold (VT) 6-minute walk test Achieve VT Did not achieve VT averaged per each minute during the test, which allowed for the identification of patients who achieved VT. For this, patients were supposed to have completed the test without stopping after intermittent claudication symptoms. Thus, patients were divided into two groups: those who did not achieve VT and those who did achieve VT during ground walking. Statistical Analysis All statistical analyses were made in the Statistical Package for the Social Sciences software – SPSS/PASW version 20 (IBM Corp, New York, USA). Normality of data was checked by the Shapiro-Wilk test. Continuous variables were summarized as mean and standard deviation, whereas categorical variables were expressed as relative frequency. Patients were grouped according to whether or not they achieved VT, and the clinical characteristics between groups were compared by the independent t-test for continuous variables and the chi-square test for categorical variables. Multiple logistic regression was conducted to identify whether demographic data, cardiovascular risk factors, comorbid conditions, ABI and walking capacity are predictors of achieving VT during the 6-minute walk test. To this end, stepwise backward techniques were used to enter covariates into themodel using only variables with p<0.30 in the bivariate analyses. In the multiple regression, only variables with p<0.05 remained in the final model. The Hosmer-Lemeshow test was used to assess the model’s goodness-of-fit. The significance level was set at p < 0.05 for all analyses. Results One hundred and thirty-three patients performed the 6-minute walk test. Among them, 63 stopped during the test due to claudication symptoms and were excluded from the analysis. Among the 70 patients who did not stop during the test, the VT was achieved during the 6-minute walk test by 42 patients (60%) and was not achieved by 28 patients (40%). Table 1 shows the comparison of clinical characteristics of patients who achieved and who did not achieve the VT during 6-minute walk test. VO 2 at VT obtained during the treadmill test was higher in patients who did not achieve VT during the 6-minute walk test in comparison with patients who achieved it (p < 0.05). Moreover, the ankle brachial index was higher in patients who did not achieve VT in comparison with patients who did (p < 0.05). Table 2 shows the predictors to achieve the VT during the 6-minute walk test. Women were less likely to achieve VT during 6-minute walk test than men (p < 0.05). Moreover, patients with higher VO 2 at VT were less likely to achieve the VT during 6-minute walk test (p < 0.05). Table 3 shows the comparisons by sex. In women, the prevalence of obesity was higher and cardiorespiratory fitness was lower as compared to men (p < 0.05). VO 2 peak in both the 6-minute walk test and the treadmill test was higher in men than in women (p < 0.05). Discussion The main findings of the study were: a) 60% of symptomatic PAD patients did achieve the VT during 6 minute-walk test, and b) women and patients with higher VO 2 at VT obtained during the treadmill test were less likely to achieve VT in the 6-minute-walk test. VT is defined as the exercise intensity above whichmetabolic predominance changes from aerobic to anaerobic, 8 providing information about aerobic capacity during exercise. In patients with symptomatic PAD, VT have been associated with walking tolerance and disease severity. 9,10 In this study, 60% of patients achieved VT in the 6-minute walk test, indicating that for most patients with symptomatic PAD this ground walking is a relatively high-intensity exercise. This could partially explain the lower daily physical activity levels and higher time spent in sedentary behavior in these patients. 25,26 Therefore, the intensity in which ground walking is performed by most patients with PAD demands a fairly high effort, which suggests that this exercise has potential to improve functional capacity of patients with PAD and, therefore, endorses the use of home-based programs to improve cardiorespiratory fitness. On the other hand, almost 40% of the patients did not achieve VT in the 6-minute walk test. The most plausible hypothesis for part of PAD patients not achieving VT was that the ground walking was not intense enough to elicit VT achievement. This hypothesis is corroborated by the fact that patients with higher cardiorespiratory fitness were less likely to achieve the VT during ground walking. Women were less likely to exceed VT during the 6-minute walk test thanmen, indicating that ground walking is performed at a lower relative intensity by women than by men. This is surprising given previous studies 27,28 have shown that women with symptomatic PAD have lower walking capacity, 29,30 are less physically active 29,30 and report more barriers to practicing physical activity compared to men. 31 In addition, women present more adverse calf muscle characteristics and lower VO 2 peak than men. 32 488