Linear and nonlinear analysis of heart rate variability in essential hypertensive patients.

Chronic high blood pressure can cause damages to the cardiovascular system. Linear analysis of hypertensive?s interbeat intervals have shown a diminished heart rate variability. Recurrence quantification analysis allows the study of short, nonstationary time series. Although some studies have shown an enhanced recurrence activity in the heart?s dynamics of hypertensive patients, there is a lack of research on essential hypertension under pharmacological treatment. We perform linear and nonlinear analyzes to study the heart rate variability (HRV) of eight hypertensive patients and eight normotensive people. Interbeat intervals series of 5 min were obtained for each participant in a sitting position. In the linear approach, we consider the mean heart rate (HR), the standard deviation of heart rate (SDHR), total power (TP), low (LF) and high (HF) spectrum frequencies of the fast Fourier transform. In the recurrence quantification analysis (RQA), we consider 12 measures. We found lower TP (ms2), LF (ms2) and HF (ms2) levels, but higher RQA values in the hypertensive group. These findings suggest a reduced HRV and an increased recurrence in the cardiac dynamic in the hypertensive sample. Also, we determined for each group, the Lyapunov exponent in the ECG recording to verify the hypothesis that heart activity is chaotic in normal conditions. We found that hypertensive group lost chaotic behavior, while the normotensive group had chaotic nature.