ABC | Volume 110, Nº2, February 2018

Original Article Amaral et al Autonomic and vascular control in prehypertensive patients Arq Bras Cardiol. 2018; 110(2):166-174 groups, 13 standard deviation of 0.21 ms², alpha errors of 5% and beta of 20%, 7 individuals in each group would be needed. The sample consisted of 25 volunteers, subdivided according to blood pressure levels in the normotensive groups (SBP < 121 mmHg and / or DBP < 80 mmHg; n = 14) and prehypertensive (SBP between 121 and 139 mmHg and/or DBP between 80 and 89 mmHg, n = 11). 14 All volunteers had FHSAH defined as father, mother, or both with a diagnosis of SAH, which was evaluated by means of a questionnaire. Inclusion criteria adopted were age between 18 and 40 years, SBP lower than 140 mmHg, DBP lower than 90 mmHg and not involved in systematized physical exercises for at least six months prior to the research. In addition, only volunteers who had blood test results within 30 days prior to the start of the study in their medical records were included. Individuals with cardiometabolic diseases, smoking or drug treatment that could interfere with the cardiovascular system were not included. This studywas approved in the Committee of Ethics inHuman Research of the HU / UFJF under the opinion nº 720/370. All volunteers signed the Free and Informed Consent Form. Measures and procedures Anthropometry For body mass and height measurements, we used, respectively, a scale with a precision of 0.1 kg and a stadiometer with a precision of 0.5 cm coupled to it (Líder®). The body mass index was calculated by dividing the body mass by the squared height (kg / m²). 15 Waist circumference was measured using an inextensible metric tape (Cescorf®), with an accuracy of 0.1 cm. All of these variables were measured according to the criteria established by the American College of Sports Medicine. 16 Blood pressure, heart rate and respiratory rate With the volunteer at rest and in supine position, blood pressure (BP), heart rate and respiratory rate were monitored simultaneously for 15 minutes. Beat-to-beat BP was monitored by digital infrared photoplethysmography (FinometerPRO®) on the volunteer's dominant arm. Cardiac and respiratory rates were recorded continuously (Biopac®) using electrocardiogram in lead II and thoracic piezoelectric tape, respectively. All acquired signals were reconstructed, digitized and recorded in a microcomputer with a sampling frequency of 1 kHz and 16-bit resolution for further analysis. Forearm muscle blood flow and vascular conductance during rest and reactive hyperemia Forearm muscle blood flow was evaluated using venous occlusion plethysmography (Hokanson® Plethysmograph). The volunteer was placed in dorsal decubitus position and the non-dominant forearm was raised above the level of the heart to ensure adequate venous drainage. A silicon tube filled with mercury, connected to the low‑pressure transducer and the plethysmograph, was placed around the volunteer's forearm, five centimeters away from the humeral-radial joint. One cuff was placed around the wrist and another at the top of the volunteer's arm. The wrist cuff was inflated at supra-systolic pressure level (200 mmHg) one minute before the measurements started and was kept inflated throughout the procedure. At 15-second intervals, the cuff placed on the arm was inflated at supra venous pressure (60 mmHg) for seven to eight seconds, then was deflated rapidly and maintained for the same period. This procedure totaled four cycles per minute. The increase in tension in the silicone tube reflected the increase in forearm volume and, consequently, in an indirect way, increased forearm muscle blood flow, reported in ml/min/100 ml. The signal of the forearm muscle blood flow wave was acquired in real time in a computer through the Non Invasive Vascular Program 3 . The evaluation of peripheral vascular conductance was performed by dividing the peripheral vascular blood flow by the mean BP (mmHg), multiplied by 100 and expressed in "units". 17 After measuring the forearm blood flow at rest for three minutes, the occlusion cuff positioned on the arm was inflated to 200 mmHg for five minutes. One minute before its deflation, the cuff placed on the wrist was also inflated to 200 mmHg remaining thus until the measurement was completed. After five minutes of occlusion, the arm cuff was rapidly deflated to induce reactive hyperemia and blood flowwas recorded for the next three minutes, maintaining the cycle protocol, inflating to 60 mmHg for 10 seconds followed by 10 seconds of deflation. 18 It was considered peak flow, the value of the first wave flow after the onset of reactive hyperemia. During the evaluation of the blood flow of the forearm at rest and the protocol of reactive hyperemia, BP was measured beat‑to-beat (FinometerPRO®). Additionally, during the rest period, cardiac output, left ventricular contractility (dP/dT maximum) and total peripheral resistance were also measured by the same equipment. In order to calculate the cardiac index, the cardiac output was corrected by the body surface area. 19 Cardiac and peripheral autonomic modulation The variabilities of the iRR, SBP and respiratory activity were evaluated in the frequency domain by autorregressive spectral analysis. In stationary segments of 250 to 300 points, the time series of the iRR, respiration and SBP were decomposed into their frequency components by the autoregressive method using the Levinson-Durbin feature and the Akaike criterion for the choice of model order. 20 This procedure allowed the automatic quantification of the central frequency and power of each relevant component of the spectrum. The spectral components of the frequency band between 0 and 0.04 Hz were considered very low frequency (VLF), the frequency band between 0.04 and 0.15 Hz was considered low frequency (LF) and the frequency band between 0.15 and 0.40 Hz, synchronized with respiration, considered 167