Nonlinear analyses of heart rate variability in hypertension

Abstract

Objective: The autonomic nervous system plays an important role in blood pressure regulation and in the development of hypertension. Heart rate variability (HRV) may be of importance in identifying subjects at higher risk of developing hypertension. In the present study, comparative analysis of HRV for normal and hypertension subjects using nonlinear indices has been carried out.

Patients and methods: We analyzed the data from 24 patients with essential hypertension aged 45-55 (HG). All the subjects in this group had a confirmed diagnosis of the first- or second-stage essential hypertension. The control group for these subjects included 32 healthy volunteers of the same age group (CG). We analyzed the whole 5minutes of the ECG recording. Nonlinear indices D₂, K₂ and lagged Poincaré plot indices were calculated.

Results: Values of D₂ and K₂ in hypertension state is statistically significantly lower than in healthy. Poincaré plot indices SD1 and SD2 in healthy volunteers are statistically higher than in hypertensive patients for all lags (P<0,05). SD1/SD2 ratio is also higher in healthy subjects, but the difference is statistically significant only for l=5 and 6.

Conclusion: The heart rhythm in groups with hypertension is more regular, its dynamics are less complex and less "chaotic," compared to healthy ones. This is expressed in lower values of entropy and correlation dimension. The HR stabilization is observed at both short and long time intervals, but mainly due to the decrease in the difference of the "neighboring" R-R intervals.

Keywords: Analyses non linéaires; Autonomic nervous system; Fréquence cardiaque; Heart rate; Hypertension; Lagged Poincaré plot; Nonlinear analyses; Parcelle de Poincaré retardée; Système nerveux autonome.