ABC | Volume 111, Nº5, November 2018

Original Article Lima et al High-intensity interval training and heart failure Arq Bras Cardiol. 2018; 111(5):699-707 After measurements of brachial artery diameter were taken at baseline, a sphygmomanometer was inflated on patient’s left forearm with 50 mmHg above the systolic BP, remaining there for 5 minutes. Sixty seconds after deflation of the sphygmomanometer cuff, a new image was recorded synchronized with the R wave of the electrocardiogram to identify the artery diameter, enabling FMD measurements. After 15 minutes (for normalization), the artery diameter was measured again. Then, a dose (0.4 mg) of nitroglycerin spray was administered sublingually. After 5 minutes, another image was recorded to measure endothelium-independent dilation. These data were obtained before exercise and 30 minutes after the HIIT session. FMD was expressed as the relative change in brachial artery diameter during the hyperemic phase, as follows: [(post-hyperemic diameter – baseline diameter) / baseline diameter] × 100. High-intensity interval training protocol The HIIT session was performed on a treadmill according to the protocol recommended by the European Society of Cardiology (ESC). 15 The session started with an 8-minute warm‑up at moderate intensity followed by four blocks of 4 minutes each at 85-95% maximal heart rate, 15 to 17 on Borg rating of perceived exertion scale, 29 alternated with 3minutes at 60-70%maximal heart rate, 11 to 13 on Borg scale. It ended with 3 minutes of cool-down at moderate intensity, totaling 36 minutes. The heart rate target zone stipulated for each block was based on the maximal heart rate reached at cardiopulmonary exercise testing and was continuously measured during training through 12-lead electrocardiographic monitoring (Nihon Kohden Corporation, Tokyo, Japan). Statistical analysis Data were analyzed using SPSS, version 20.0. Categorical variables are described as absolute frequencies and percentages. Continuous variables with normal distribution are described as means and standard deviations. The only variable without normal distribution (VE/VCO 2 slope) was described as median and interquartile range. After meeting the assumptions of normality, the Student t-test for paired samples was used to compare means of the endothelial function variables (brachial artery diameter, FMD, and endothelium-independent dilation) pre- and post-exercise. Generalized estimating equations (GEE) were used to compare mean BP and heart rate between four different moments during the experiment. In all analyses, p <0.05 was considered statistically significant. Results Initially nineteen patients were included in the study. After the first evaluation, two patients who did not complete the cardiopulmonary exercise testing and one who had a limiting medical condition were excluded, as shown in Figure 1. Table 1 shows the demographic, anthropometric, and clinical characteristics of the sample. All patients presented normal ejection fraction, reduced left ventricular end-diastolic volume index and increased filling pressure, as shown in table 2. However, eight patients presented 15 > E/e’ > 8. Among these individuals at least one diagnostic criterion for HFpEF was confirmed. Reduced functional capacity and increased ventilatory inefficiency were identified by cardiopulmonary exercise testing. The mean peak respiratory exchange ratio > 1.1 was reach as maximality criterion as shown in table 3. All patients tolerated exercise and completed the experimental session. Exercise protocol variables are described in table 4. One single HIIT session promoted subacute increase of 0.37 ± 0.44 mm in brachial artery diameter, as shown in Figure 2. This increase was also observed in brachial artery diameter post-hyperemia. However, when these data were used to calculate pre- and post-HIIT variation in the artery diameter, there was no difference in absolute FMD and relative FMD. Also, there was no difference in the brachial artery diameter pre-NTG (Nitrogen) and post-NTG. Similarly, there was no difference in absolute endothelium-independent dilation and relative endothelium-independent dilation after one HIIT session, as presented in table 5. Baseline systolic and diastolic BP were 138 ± 21 mmHg and 81 ± 11 mmHg, respectively. Figure 3 shows variation in BP at four different points in time of the experiment. A significant reduction in systolic BP was observed 5 and 30 minutes after the HIIT session compared to the first measurement. There was no difference in diastolic BP and mean BP before and after the HIIT session. Discussion To our knowledge, this is the first study to show that one single session of HIIT is effective in promoting a significant subacute increase in brachial artery diameter, which was accompanied by a significant reduction in systolic BP in patients with HFpEF. Borlaug et al. 9 demonstrated that these individuals have global dysfunction in cardiovascular reserve, showing an impaired reduction in systemic vascular resistance and a blunted increase in blood flow while exercising. According to the authors, these phenomena are potential contributors to limited functional capacity in this situation. Patients with HFpEF in our sample showed vasodilation after one single HIIT session suggesting that this type of exercise is a stimulus capable of promoting subacute systemic vasomotor changes, even in patients with impaired ventricular‑arterial coupling 9-11 and chronic vascular dysfunction. 6,8,30 It is important to mention that some acute and subacute physiological responses to exercise may be clinically relevant. These responses can be superimposed after consecutive exercise sessions are carried out as a temporal summation and they may contribute to chronic adaptations of exercise training. 31 Thus, successive sessions of exercise that increase blood flow, shear stress and, consequently, bioavailability of nitric oxide, may be a key mechanism for chronic adaptations in peripheral hemodynamics. 32 Fu et al. found that after 12 weeks of HIIT, patients with HFpEF increased the VO 2 peak and improved peripheral hemodynamics, through increased blood distribution and oxygen extraction by the musculature while exercising. 33 701