Effects of Coexistence Hypertension and Type II Diabetes on Heart Rate Variability and Cardiorespiratory Fitness / Efeitos da Coexistência de Diabetes Tipo 2 e Hipertensão sobre a Variabilidade da Frequência Cardíaca e Capacidade Cardiorrespiratória

Abstract Background: Type 2 diabetes Mellitus (T2DM) is associated with cardiac autonomic dysfunction, which is an independent predictor of mortality in chronic diseases. However, whether the coexistence of systemic arterial hypertension (HTN) with DMT2 alters cardiac autonomic modulation remains unknown. Objective: To evaluate the influence of HTN on cardiac autonomic modulation and cardiorespiratory fitness in subjects with DMT2. Methods: 60 patients of both genders were evaluated and allocated to two groups: DMT2 patients (n = 32; 51 ± 7.5 years old) and DMT2 + HTN patients (n = 28; 51 ± 6.9 years old). RR intervals were obtained during rest in supine position. Linear and nonlinear indices of heart rate variability (HRV) were computed using Kubios HRV software. Pulmonary gas exchange was measured breath-by-breath, using a portable telemetric system during maximal incremental exercise testing on a cycle ergometer. Statistical analysis included Shapiro-Wilk test followed by Student's t Test, Pearson correlation and linear regression. Results: We found that patients in the DMT2+HTN group showed lower values of mean RR intervals (801.1 vs 871.5 ms), Shannon entropy (3 vs 3.2) and fractal dimension SD 1 (9.5 vs 14.5), when contrasted with patients in the DMT2 group. Negative correlations were found between some HRV nonlinear indices and exercise capacity indices. Conclusion: HTN negatively affects the cardiac autonomic function in diabetic patients, who are already prone to develop autonomic dysfunction. Strategies are need to improve cardiac autonomic functionality in this population.

Resumo Fundamento: A diabetes mellitus tipo 2 (DM2) está associada com disfunção autonômica cardíaca, que é um preditor independente de mortalidade em doenças crônicas. No entanto, ainda não se sabe se a coexistência de hipertensão arterial sistêmica (HAS) e DM2 altera a modulação cardíaca autonômica. Objetivos: O objetivo deste estudo foi avaliar a influência de HAS sobre a modulação da função autonômica cardíaca e capacidade cardiopulmonar em indivíduos com DM2. Métodos: 60 pacientes de ambos os sexos foram avaliados e alocados em dois grupos; pacientes DM2 (n = 32; 51 ± 7,5 anos) e pacientes DM2 + HAS (n = 28; 51 ± 6,9 anos). Intervalos RR foram obtidos durante repouso e em posição supina. Índices lineares e não lineares da variabilidade da frequência cardíaca (VFC) foram registrados utilizando-se o programa Kubios HRV software. A troca gasosa pulmonar foi medida a cada inspiração, utilizando-se um sistema telemétrico portátil durante o teste incremental máximo de exercício em cicloergômetro. A análise estatística incluiu o teste Shapiro-Wilk seguido do teste t de Student, a correlação de Pearson e a regressão linear. Resultados: Encontramos que pacientes do grupo DM2+HAS apresentaram valores mais baixos de intervalos RR (801,1 vs 871,5 ms), entropia de Shannon (3,0 vs 3,2) e DP1 da dimensão fractal em comparação aos pacientes do grupo DM2. Foram encontradas correlações negativas entre alguns índices não lineares da VFC e índices da capacidade do exercício. Conclusão: A HAS afeta negativamente a função autonômica cardíaca em pacientes diabéticos, os quais já são propensos a desenvolverem disfunção autonômica. Estratégias são necessárias para melhorar a função autonômica cardíaca nessa população.

Is heart rate variability a feasible method to determine anaerobic threshold in progressive resistance exercise in coronary artery disease?

ABSTRACT Background Recent studies have shown that the magnitude of the metabolic and autonomic responses during progressive resistance exercise (PRE) is associated with the determination of the anaerobic threshold (AT). AT is an important parameter to determine intensity in dynamic exercise. Objectives To investigate the metabolic and cardiac autonomic responses during dynamic resistance exercise in patients with Coronary Artery Disease (CAD). Method Twenty men (age = 63±7 years) with CAD [Left Ventricular Ejection Fraction (LVEF) = 60±10%] underwent a PRE protocol on a leg press until maximal exertion. The protocol began at 10% of One Repetition Maximum Test (1-RM), with subsequent increases of 10% until maximal exhaustion. Heart Rate Variability (HRV) indices from Poincaré plots (SD1, SD2, SD1/SD2) and time domain (rMSSD and RMSM), and blood lactate were determined at rest and during PRE. Results Significant alterations in HRV and blood lactate were observed starting at 30% of 1-RM (p<0.05). Bland-Altman plots revealed a consistent agreement between blood lactate threshold (LT) and rMSSD threshold (rMSSDT) and between LT and SD1 threshold (SD1T). Relative values of 1-RM in all LT, rMSSDT and SD1T did not differ (29%±5 vs 28%±5 vs 29%±5 Kg, respectively). Conclusion HRV during PRE could be a feasible noninvasive method of determining AT in CAD patients to plan intensities during cardiac rehabilitation.