IJCS | Volume 31, Nº2, March / April 2018

148 18 16 14 12 10 8 6 4 2 0 T1 T2 T3 T4 T5 T6 T7 11.76 – VO 2 at the CPETAT 13.7 15.9 CPET peak VO 2 VO 2 (mL.kg –1 .min –1 ) Figure 2 – Longitudinal progression of the relative VO 2 (mL/kg/min -1 ) during the 6MWT2. HFNEF: heart failure with normal ejection fraction; CPET: cardiopulmonary exercise test; VO 2 : oxygen consumption (mL.kg -1 .min -1 ); T1: time zero of the 6MWT (baseline conditions); T2, T3, T4, T5, T6, T7: first, second, third, fourth, fifth, and sixth minutes of the 6MWT, respectively, AT: anaerobic threshold. Teixeira et al. Gas Analysis in the 6-MinuteWalkTest in HFNEF Int J Cardiovasc Sci. 2018;31(2)143-151 Original Article low correlation with the walked distance in the 6MWT (r = 0.28 and r = 0.24, respectively). Such discrepancies could be attributed to different methodologies of the 6MWT and the type of ergometers used. The HFREF studies found in the literature assessing the 6MWTwith portable gas analyzers and performed in a hallway were: Riley et al., 6 Foray et al., 7 Faggiano et al., 8 and Kervio et al. 10 Guimarães et al. 9 , in turn, used the gas analyzer during two 6MWT tests performed on a treadmill, also in patients with HFREF. In regards to HR parameters, the study group showed more stable values after the second minute of the 6MWT (T3). Kervio et al. 10 highlight that earlier achievement of a stable state reflect better clinical conditions and, therefore, less severe ones. The HR at the end of the 6MWT was 85.7% of the CPET maximum HR, which is similar to the percentage values of the peak VO 2 in the 6MWT in relation to the CPET peak VO 2 . It is noteworthy that the final HR in the 6MWT was similar to the HR in the CPET AT, reinforcing that the 6MWT represents an intense effort, carried out at the level of or above the CPET AT in patients with HF. 6-8,10 Despite the authors’ claim that patients with HFNEF present HR alterations in the first minute of recovery (HR1Rec) 22 and the fact that there are no data in the literature related to the 6MWT, if we consider the recommended value of 12 bpm, this value was within the normal limits both in the T6M as well as in the CPET. 23 The chronotropic index analysis demonstrated a chronotropic incompetence, even if we consider the use of beta-blockers (normal > 0.60), both in relation to the 6MWT as well as to the CPET, as found in the literature. 24 The maximum O 2 pulse in the 6MWT and the CPET showed no difference between the two tests, yielding reduced pulse O 2 values in relation to the predicted one (< 85%), around 70%, and with absolute values below 12 mL.kg -1 .min -1 /bpm, which is considered of poor prognosis. 25 In relation to the two ventilatory variables analyzed, no difference in the VE/VCO 2 slope was observed. The VE/VCO 2 slope values are within the values cited as indicative of good prognosis (< 30), 13 and this fact associated with the lack of difference between the two tests can reinforce the prognostic ability of the 6MWT. The ventilatory power (VP) analysis also showed a difference between the two tests, with higher values for the CPET. The VP, which combines the response of the SBP with the VE/VCO 2 slope (VP = SBP x VE/VCO 2 slope) 26 showed a difference probably due to the higher SBP in the CPET. However, good prognosis values (> 3.5) were observed for both tests. 26 The RQ is a criterion to obtain intense (> 1.0) or maximum effort in exercises of increasing intensity (> 1.15). 13 There was no difference between the maximum RQ values between the two tests. The data found here are in agreement with those found by Kervio et al., 10 who consider the RQ in the 6MWT as reflecting intense effort. Both in the populationwithHFREF 10 and in patients with HFNEF in the study, 50% of each sample obtained an