6.3 Signals of the Cardiovascular System

|

271

plot(tau_p2,s_p2,'rv','MarkerFaceColor','r');

axis([150/8, 170/8, 400, 1700])

xlabel('\tau / s');

ylabel('AKF');

title('Autocorrelation');

hold off

%

Calculation of LVET

L_T = (tau_p2-tau_p1)/8

figure(6); hold on;

% Plot of LVET result

strb = ['The medium LVEST is: ', num2str(L_T), ' ms.']

annotation('textbox',[0.1 0.4 0.8 0.4],'String',strb,'FontSize',11,...

'LineStyle','none','BackgroundColor', [1 1 1]);

set (gca, 'visible', 'off')

For the presented phonocardiogram, this results in an LVET of 314 ms.

6.3.2.1 Phonocardiogram of Mechanical Prosthetic Heart Valves

A completely different form of phonocardiography application is the control of mech-

anical prosthetic heart valves. These usually consist of a ring-shaped housing in which

two valve leaflets are suspended. The valve leaflets can be opened in one direction so

that they are perpendicular to the blood flow. In the other flow direction, the flap sails

close with the housing and thus block the backflow. In this way, the desired valve func-

tion is achieved. A textile ring is attached to the outside of the housing, with which

the prosthesis is sewn into the heart. The material of the housing and valve leaflet is

usually pyrolytically deposited carbon, which has a very smooth surface, to prevent

the adhesion of thrombi. Mechanical prosthetic heart valves are the treatment option

along with biological prostheses, when a native heart valve needs to be replaced due

to a defect. Despite the very smooth surfaces of mechanical prosthetic heart valves,

there is an increased risk of thrombus adhesion, which is why anticoagulants must be

used to reduce blood clotting in patients with mechanical heart valve replacement. If

anticoagulation therapy is inadequate, thrombi can adhere to the valve body and leaf-

lets and impair valve function (see Figure 6.41) – sometimes with fatal consequences.

Mechanical prosthetic heart valves generate high-frequency sounds when the valve

leaflets open and close, which are closely related to the mechanical function of the

prosthesis. Figure 6.42 shows the sound pattern of a two-leaflet prosthesis in the aor-

tic position over one cardiac cycle. An initial fainter murmur occurs when the valve

leaflets open. This begins the ventricular expulsion phase. Once the ventricle is emp-

tied at the end of the expulsion phase, reflux begins, causing the valve leaflets to close.

This is accompanied by a hard impact of the valve leaflets, which produces a loud im-