ABC | Volume 111, Nº1, July 2018

Original Article Bassi et al T2DM and HTN on HRV and cardiorespiratory status Arq Bras Cardiol. 2018; 111(1):64-72 normalized units. 22 STD RR represents a global index of HRV and reflects all the cyclic components responsible for variability in the recording period; RMSSD reflects alterations in autonomic tone that are predominantly vagally mediated; the geometrical HRV indices are an estimate of the overall HRV. 23 However, reference values for these parameters, available in the literature, were obtained in healthy subjects aged from 40 to 60 years –rMSSD from 33.39 to 28.77 (ms) for male and from 30 to 25.80 (ms) for female; HFnu from 22.85 to 24.51 for male and from 27.74 to 27.94 female; LFnu from 77.07 to 75.49 for male and from 72.26 to 72.06 for female; LF/HF from 3.36 to 3.08 for male and from 2.60 to 2.58 female. Reference values for nonlinear variables are also available only for the same age – SD1 from 24.01 to 20.56 for male and from 21.55 to 18.44 (ms) for female and SD2 from 198.61 to 185.20 for male and from 176.15 to 165.41 (ms) for female. 24 Laboratorial exams Blood samples were obtained after an overnight fast. HbA1c was measured in a central laboratory by anion‑exchange high-performance liquid chromatography (Variant II, Bio Rad, Berkeley, California), coupled with a fluorescence detector method certified by the National Glycohemoglobin Standardization Program. 25 Insulin resistance was evaluated by HOMA–IR using the following formula: (fasting plasma glucose [mg/dL] x fasting plasma insulin [µU/mL] / 22.5). 25 Fasting plasma glucose was measured by an enzymatic method using an AU 680® (Beckman Couter, Suarlée, Namur, Belgium) and fasting plasma insulin was measured by a chemiluminescent assay (UniCel® DxI 800, Pasadena, California, USA). Total cholesterol (total-C), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides were measured by an enzymatic method using the AU 680® (Beckman Couter, Suarlée, Namur, Belgium). The Brazilian Society of Diabetes criteria for metabolic control were used as reference values – HbA1c 7% or 53 mmol/mol and fasting plasma glucose < 110 mg/dL. 26 Cardiopulmonary exercise testing (CPET) A symptom-limited incremental exercise test was performed on a cycle ergometer (Recumbent Corival of MedGraphics - Minnesota, USA.). Gas exchange and ventilatory variables were recorded during the test using a calibrated computer-based exercise system (Metabolic analyzer System Greenhouse telemetry module for field studies Oxycon-Mobile, Jaeger, Hoechberg, Germany). The day before the CPET, subjects were taken to the experimental room for familiarization with the procedures and equipment to be used. All subjects were evaluated in themorning to avoid circadian influences on their physiological responses. All subjects were instructed to: (i) avoid caffeinated and alcoholic beverages or any other stimulants (drinks, foods or medications) the night before and the day of data collection; and (ii) not to perform activities requiring moderate-to-heavy physical exertion on the day before data collection. The tests were carried out under controlled relative air humidity and temperature conditions. Before the CPET, the exercise protocol was described to each subject by a member of our group. 27 Peak VO 2 was defined as the highest VO 2 value during the last 15 seconds of exercise. 28 Fifteen second averaged ventilation (V E ) and carbon dioxide production (VCO 2 ) data, obtained from the initiation of exercise to exercise peak, were input into Microsoft Excel, Microsoft Corp., Bellevue, WA, USA). Outcome measures Primary outcome: The primary outcome measures were the HRV indices, able to detect abnormalities in the cardiac autonomic system regulation. Secondary outcome: As a secondary outcome measure, the exercise capacity was assessed by CP and VP, both of which have been showed to serve as a surrogate predictor of mortality and prognosis. 16 Statistical analysis Data are reported as mean ± SD. All data were verified for the assumptions of normality, and comparisons between groups (T2DM vs T2DM+HTN) were performed using unpaired t tests. The categorical variables were presented in percentage (absolute number) and the comparisons between the groups of these variables were performed by means of the chi-square test. Statistical analyses were performed using Statistica 5.5 (StatSoft Inc., Tulsa, USA). Pearson’s product moment correlation coefficient was used to examine the relationship between linear and nonlinear indices and cardiorespiratory variables. The magnitude of the correlations was determined considering the following classification scheme for r-values ≤ 0.35 low or weak; r = 0.36 ≤ 0.67 moderate; r ≥ 0.68 strong or high; r ≥ 0.9 very high; r = 1 perfect. 29 The probability of a type I error was set at 5% for all tests ( α = 0.05). Results Subject characteristics A total of 60 patients were evaluated over a 1-year period. Table 1 shows demographic, anthropometric and clinical characteristics of subjects in the two groups (DMT2 and DMT2+HTN). There were no significant differences between groups in baseline characteristics (age, height, and duration of T2DM). However, BMI was higher in the group of patients with both diseases (p = 0.03). However, no other body composition measurements were performed in order to better characterize the body status. There were no significant differences regarding other risk factors for CVD and oral hypoglycemic medications. Additionally, insulin and HOMA-IR were significantly higher in T2DM + HTN when compared to T2DM, indicating higher insulin resistance. Therewere no significant differences for fasting plasma glucose, total-C, LDL-C, HDL-C and HbA1c. The HRV indices are presented in Table 2. Mean values of RR intervals and the nonlinear indices SD1, Shannon entropy and ApEn were significantly lower in T2DM +HTN when compared to T2DM. 66