Force plate monitoring of human hemodynamics

Abstract

Background: Noninvasive recording of movements caused by the heartbeat and the blood circulation is known as ballistocardiography. Several studies have shown the capability of a force plate to detect cardiac activity in the human body. The aim of this paper is to present a new method based on differential geometry of curves to handle multivariate time series obtained by ballistocardiographic force plate measurements.

Results: We show that the recoils of the body caused by cardiac motion and blood circulation provide a noninvasive method of displaying the motions of the heart muscle and the propagation of the pulse wave along the aorta and its branches. The results are compared with the data obtained invasively during a cardiac catheterization. We show that the described noninvasive method is able to determine the moment of a particular heart movement or the time when the pulse wave reaches certain morphological structure.

Conclusions: Monitoring of heart movements and pulse wave propagation may be used e.g. to estimate the aortic pulse wave velocity, which is widely accepted as an index of aortic stiffness with the application of predicting risk of heart disease in individuals. More extended analysis of the method is however needed to assess its possible clinical application.

Figure 1

Typical example of the first averaged curvature during the pulse wave propagation. The first averaged curvature of the force plate signal is compared with times when the pulse wave reaches certain morphological structures (labeled vertical lines). The labels represent: 1 – aortal root; 2 – truncus brachiocephalicus; 3-top of the aortal arch; 4 – below the diaphragm; 5 – origin of renal arteries; 6 – the bifurcation of the abdominal aorta to the common iliac arteries; 7 – junction of the external iliac artery and femoral artery. The time counting starts at the maximum of the ECG R wave. The inset displays the first (crosses), second (squares) and third (circles) averaged curvatures referring to a marked time interval.

Figure 2

Typical example of the first averaged curvature during the whole heart cycle. The first averaged curvature is plotted as a function of time (full line) together with the pressure measured in the left ventricle (dashed line) and in the aortal root (dotted line). The moments when the pulse wave reaches certain morphological structures are labeled with dashed vertical lines. The numbers have the same meaning as on the Figure 1. The inset a) displays the marked peak (atrial contraction) together with the derivative of the ventricular pressure. The inset b) shows the averaged curvature peak corresponding to the rapid filling together with the derivative of the ventricular pressure.

Figure 3

The probability distributions of the peak localizations of the first curvature. The probability distributions obtained during 300 subsequent heart beats of a selected individual. The distributions refer to the peaks 1, 2, 5 and 7 of the figure 1. The times of the pulse wave arrival obtained during catheterization are plotted as dashed lines.

Figure 4

Sketch of a helix.