IJCS | Volume 32, Nº4, July/August 2019

363 study. Statistically significant differences were found for VO 2 max between the two methods (BP - 42.31 ± 5.21 ml/ kg.min vs. CPET - 30.46 ± 5.50 ml/kg.min., p < 0.0001). The Bruce formula overestimated the result by 34.1% (BP - 45.95 ± 3.94 ml/kg.min vs. CPX - 34.27 ± 4.20 ml/ kg.min, p < 0.0001) for men, and by 44.8% (BP - 38.84 ± 3.72 ml/kg.min vs. CPX - 26.83 ± 3.90, p < 0.0001) for women. A moderate correlation was observed between the methods (r = 0.65). When classifying the results according to the table of aerobic capacity of the American Heart Association, the agreement was null (kappa = 0.0034; Pearson chi2 = 0.001). Conclusion: VO 2 estimated by BP is not capable of demonstrating the true aerobic capacity in these individuals, while CPET is an important tool for early detection of diminished functional capacity in sedentary young men and women. Introduction Maximal oxygen uptake (VO 2 max) is the product of the arteriovenous oxygen difference and cardiac output. 1,2 It is the most important physiological measurement in defining functional capacity of an individual (aerobic power). 3 VO 2 max varies with body weight, age, physical activity level and presence of cardiorespiratory disease. 1,4,5 The parameter is used to prescribe exercise, evaluate the effects of training and therapeutic interventions, and as a risk stratification tool for the occurrence of cardiovascular disease. 3,6 VO 2 max can be directly measured by analysis of breathing gases during cardiopulmonary exercise testing (CPET) or estimated by the stress test using prediction equations. 2 Physical fitness has been shown in several studies to be an important predictor of all-cause and cardiovascular mortality. 7-12 On the other hand, a sedentary lifestyle is an important cardiovascular risk factor, with increasing prevalence in the world population. 13 The Bruce protocol (BP) is the main non-invasive method for cardiovascular assessment performed in asymptomatic individuals. 14 However, functional capacity estimated by formulas during the test may be inaccurate for physically inactive young individuals, leading to a wrong assessment of fitness and minimizing the real cardiovascular risk posed by a low physical fitness, commonly seen in these individuals. Aiming at evaluating the difference in functional capacity between the direct and indirect method in inactive young individuals, VO 2 max was measured by the CPET and the BP formulas. Methods Fifty healthy, non-obese and physically active individuals were invited to participate in the study. All were residents of Florianópolis city, Brazil. Nine individuals declined to participate, and 41 were then included. Participants were randomly assigned to CPET on a treadmill (Inbramed ® 1999, Brazil), with ramp protocol (ErgoPC Elite version 3.3.6.2, 1999, Micromed ® , Brazil) and gas analyzer (Metalyzer ® , 2004, Germany) or to the BP (ErgoPC13 version 2.4.8.5, 1998, Micromed ® , Brazil), with a 48 interval between the tests. The formula used to estimate VO 2 by the BP was the one available in themost popular ergometry software in Brazil: physically inactive men - VO 2 = (TIME (min) x 2.9) + 8.33. Women - VO 2 = (TIME (min) x 2.74) + 8.03. 1 The estimated predicted VO 2 for each individual was estimate by the formulas (mL/Kg.min): 3,5 ● Men: VO 2 = 60 – 0.55 x age (years); ● Women: VO 2 = 48 – 0.37 x age (years). All tests were performed by an experienced cardiologist, qualified to perform ergometric test and CPET. Treadmill tests were carried out following the Brazilian Society of Cardiology guidelines on ergometric and cardiopulmonary tests. 3 VO 2 max was considered as the highest VO 2 reached during stress (VO 2 peak). After direct or indirect measurement of VO 2 , participants were classified by cardiorespiratory fitness using the American Heart Association table and grouped into four groups – low, moderate, high and very high. 5 All participants signed the informed consent form and the study protocol was approved by the ethics committee of the institution. Statistical analysis was performed using the Stata SE 9 and the Microsoft Excel software. The Student’s t-test was used to compare means between matched samples. Correlation was analyzed by Pearson correlation. Agreements were analyzed using weighted kappa statistic. A p ≤ 0.05 was set as statistically significant. Results Twenty-one (52%) of the 41 individuals includedwere women. Mean age was 34.1 ± 8.12, varying from 21 to 50 years. Mean body mass index (BMI) was 24.5 Kg/m² ± 3.34, and mean weight and height was 72.8 ± 15.7 kg and 1.73 ± 0.11 m, respectively. Mean VO 2 max was 42.31 ± 5.21 mL/Kg.min for the BP and 30.46 ± 5.50 mL/Kg.min for the CPET with ramp protocol, p < 0.0001. Analysis by sex (Figure 1) revealed significant difference between Herdy & Souza Comparison of direct and estimatedVO 2 Int J Cardiovasc Sci. 2019;32(4):362-367 Original Article