Changes of Heart Rate Variability during Anesthesia in Hypertensive Patients by Nonlinear Dynamics

Lim, Young Jin; Kim, Hee Soo; Yeom, Jong Hoon; Shin, Woo Jong; Kim, Yong Chul; Lee, Dong Ho; Yum, Myoung Gul

Abstract

BACKGROUND: Heart rate variability (HRV) is characterized by a variety of linear, non-linear, periodic and non-periodic oscillations. The aim of the present study was mainly to investigate the characteristics of nonlinear dynamics of HRV of the hypertensive patients by anesthesia comparing with the normotensive patients.
METHODS
With informed consent, unpremedicated normotensive (n=20) and the hypertensive patients (n=22) were included in this study. ECG data were collected from 10 minutes before induction to 15 minutes after induction. Collected ECG data were stored into computer binary files. We calculated correlation dimensions (CD, degree of freedom of system), 1/f noise (beta, nonlinearity) and Hurst exponents (HE, roughness of signals) from the collected ECG data.
RESULTS
During resting state, CD of the hypertensive patients was significantly lower than that of the normotensive patients (P<0.05). During maintenance of anesthesia, there was no difference of CD between the two groups. CD of two groups were decreased significantly after anesthesia (P<0.001). The values of and HE of two groups were not different during resting state and maintenance of anesthesia. But the values of and HE of two groups were increased significantly after anesthesia (P<0.001).
CONCLUSION
As the CD of the hypertensive patients is lower than of the normotensive patients during resting state, the degree of freedom of heart rate control system of the hypertensive patients is more smaller than that of the normotensive patients. Decreasing of CD after anesthesia in two groups means that degree of freedom of heart rate control system is decreased by anesthesia. Increasing of 1/f noise after anesthesia in two groups means that nonlinearity of heart rate variability is decreased by anesthesia. Increasing of HE after anesthesia in two groups means that roughness of heart rate variability is decreased by anesthesia.