Estimation of Arterial Stiffness Based on Analysis of Pulse Rate Variability L. Kalakutskiy, A. Fedotov Samara State Aerospace University, Department of Biomedical Engineering, Samara, Russia Abstract – Hemodynamic model of human cardiovascular sys- tem has been proposed. This model allowed us to establish the relationship between arterial stiffness and indices of pulse rate variability (PRV). The difference between heart rate variability (HRV) and PRV indices in two groups of volunteers were examined. First group consisted of 20 healthy people aged 20 to 30 years and second group consisted of 30 people aged 50 to 70 years. It was revealed that the difference between HRV and PRV in- dices decreases among the elder group. According to model eval- uation it may be caused by increasing in arterial stiffness. A new approach for obtaining arterial stiffness based on esti- mation of difference between HRV and PRV indices was sug- gested. Keywords — pulse rate variability, arterial stiffness 1. INTRODUCTION Analysis of heart rate variability (HRV) is widely used as a noninvasive tool for assessing the state of autonomic regula- tion in physiological research and medical diagnostics [1-3]. HRV can be determined by processing of biosignals, which contain information about heart rate. HRV is one of the most common indicators obtained by means of R-R intervals analy- sis of ECG. Upon the registration of peripheral pulse waves by sensors of blood pressure, as well as rheographic or ple- thysmography sensors, the duration of time intervals between two consecutive systolic peaks of pulse waves is analyzed. In a number of studies [4-7], when comparing the results of the analysis of HRV (R-R intervals) and pulse rate variability (pulse beat-to-beat intervals) (PRV), some differences are revealed. In this paper an attempt is undertaken to establish a rela- tionship between PRV indices defined in the frequency do- main and the characteristics of the vascular system in order to estimate arterial stiffness. 2. MODELLING Simulation of hemodynamic processes in the cardiovascu- lar system allows determining patterns of the pulse wave propagation along the arterial bed [8]. To describe the propagation of the pulse wave (PW) in ar- teries we used equations based on the model of "elastic cham- ber", proposed by O. Frank. As a first approximation, to de- scribe the hemodynamic processes it can be assumed that the excess pressure is distributed along the elastic tube. Accord- ing to the Navier-Stokes equations we can describe hemody- namic processes as the following set of equations [8]: t Q r R Q x P g G G S U G G 2     t P Eh r G P x Q g G G S G G 2 3 2     , (1) where: x – axial coordinate, Q – flow, P – hydraulic pressure, 4 8 r R g S P  – hydraulic resistance due to the dynamic blood viscosity, here ȝ – blood viscosity, r – radius of artery; ȡ –blood density, G g – leakage flow, E – Young’s modulus of arterial wall, h – thickness of arterial wall. Changes of PW parameters in space and time are given by the solution of equations (1) with some assumptions. In model- ing a blood vessel is considered as an elastic tube without leakage that is G g = 0 and since the blood is close to an abso- lutely incompressible fluid we can neglect the second term of the first equation. On the assumption of equations (1) the fol- lowing can be written: W W W S W S W W S d P e t h t E R x r x t P t h t E t R r x g g ｳ           0 0 ) ( ) 3 3 2 2 ) ( ( 8 ) ( 2 ) ( 2 3 ) , ( 2 2 (2) where P 0 (IJ) – pressure in the vessel at the point with coordinate x = 0, E(t) – change of Young’s modulus in time IJ – integration variable For the pressure P 0 (IJ), which simulates alteration of pres- sure at the entrance of investigated vessel, we use the follow- ing description: Á. Jobbágy (Ed.): 5th European IFMBE Conference, IFMBE Proceedings 37, pp. 389–392, 2011. www.springerlink.com