IJCS | Volume 31, Nº2, March / April 2018

145 Teixeira et al. Gas Analysis in the 6-MinuteWalkTest in HFNEF Int J Cardiovasc Sci. 2018;31(2)143-151 Original Article Table 1 – Clinical characteristics of the study population Variables n = 24 % Sex male 7 29.2 female 17 70.8 Mean SD EF (%) 64.7 8.2 Weight (kg) 84.3 16.6 Height (cm) 160.2 7.4 BMI 32.9 6.7 Waist (cm) 104.4 13.3 Hip (cm) 110.8 11.6 W/H 0.944 0.086 Age (years) 59.6 10.2 Abbreviations: EF: ejection fraction; BMI: body mass index; W/H: waist-to-hip ratio; SD: standard deviation. In order to analyze the gases expired during the 6MWT and obtain the values of the variables, we used the same VO2000 in a portable mode connected wirelessly to a computer. We used the software Aerograph, version 4.3 ( Imbrasport, Porto Alegre, RS, Brazil), which organized the data for later analysis. During the 6MWT, the patient connected to the gas analyzer remained seated for 4 minutes and 30 seconds. After the values of the variables were collected during this resting period, the patient stood up for 30 seconds before initiating the 6MWT, which was performed according to the guidelines of the American Thoracic Society (ATS). 5 All patients completed the 6 minutes of walk. The gas analysis ended after the fifth minute of recovery. The maximum blood pressure (BP) considered in the analysis was the one obtained immediately after the effort, i.e. , after the sixth minute of the walk when the patient sat down and the BP was then measured between 30-40 seconds during recovery. Statistical analysis The numerical data are expressed as mean ± standard deviation (SD) since all the variables included had an approximately normal distribution (p value of the Kolmogorov-Smirnov test > 0.05). Categorical data are expressed as frequency (n) and percentage (%). The variation of the hemodynamic, metabolic, and ventilatory measurements between the tests (assessments) CPET and 6MWT were analyzed by Student's t test for paired samples. A descriptive graphic analysis was performed, presenting the mean and SD values of the measurements obtained at each minute of the variables HR and VO 2 , indicating, for each one of these variables, the maximum CPET values and values equivalent to the AT. In order to evaluate the correlation levels between the 6MWT distance and the peak VO 2 and CPET peak VO 2 , we used Pearson's correlation coefficient (r). We adopted a significance level of 5%. The statistical analysis was performed using the software SAS 6.11 (SAS Institute, Inc., Cary, NC, USA). Results A total of 24 patients were evaluated. Of these, 22 underwent both tests (CPET and 6MWT) while two underwent only the CPET; thus, the comparison between the CPET and 6MWT included only data of 22 patients. Table 1 shows the baseline characteristics of the study population. There was a predominance of the female gender (70.8%) and obesity (58.3%). Hypertension was present in 100.0% of the patients.