Biomedical Engineering Reference
In-Depth Information
TW time
TIME is a weight function for the time delay of each node, where
TIME is a range of time delays;
N
CW speed
SPEED is a weight function for the impulse propagation speed
of each transition, where SPEED is a range of propagation speeds.
T
Property 1 (Impulse propagation time) In the heart system, the electrical im-
pulse originates from SA node (node A), travels through the entire conduction
network and terminates at the atrial muscle fibres (node C) and at the end of
Purkinje fibres in both sides of the ventricular chambers (node G and node H).
The impulse propagation time delay differs for each landmark node (N) .The
impulse propagation time is represented as the total function TW time N
P ( 0 .. 230 ) . The impulse propagation time delay for each node (N) is represented
as: TW time ( A ) =
0 .. 10, TW time ( B ) =
50 .. 70, TW time ( C ) =
70 .. 90, TW time ( D ) =
125 .. 160, TW time ( E ) =
145 .. 180, TW time ( F ) =
145 .. 180, TW time ( G ) =
150 .. 210
and TW time ( H )
=
150 .. 230.
Property 2 (Impulse propagation speed) The impulse propagation speed also dif-
fers for each transition ( i
N ). The impulse propagation speed
is represented as the total function CW speed
j , where i, j
( 5 .. 400 ) . The impulse prop-
agation speed for each transition is represented as: CW speed ( A
T
→ P
B )
=
30 .. 50,
CW speed ( A
C )
=
30 .. 50, CW speed ( B
D )
=
100 .. 200, CW speed ( D
E )
=
100 .. 200, CW speed ( E
G )
=
300 .. 400 and CW speed ( F
H )
=
300 .. 400.
Electrical activity is spontaneously generated by the SA node, located high in
the right atrium, shown as node A in Fig. 8.5 (a). The SA node is the physiologi-
cal pacemaker of the normal heart, responsible for setting its rate and rhythm. The
electrical impulse spreads through the walls of the atria, causing them to contract.
The conduction of the electrical impulse throughout the left and right atria is seen
on the ECG as the P-wave (see Fig. 8.3 ). From the sinus node, the electrical impulse
propagates throughout the atria and reaches nodes B and C, but cannot propagate
directly across the boundary between the atria and ventricles. The electrical impulse
travels outward into the atrial muscle fibres and reaches the end of the fibres, shown
as node C in the conduction network (see Fig. 8.5 (b)).
Normally, the only pathway available for the electrical impulse is to enter the
ventricles through a specialised region of cells called the AV node. The AV node
is located at the boundary between the atria and ventricles, shown as node B in
Fig. 8.4 (b). The AV node provides the only conducting path from the atria to the
ventricles. The AV node functions as a critical delay in the conduction system. With-
out this delay, the atria and ventricles would contract at the same time, and blood
would not flow effectively from the atria to the ventricles. The delay in the AV node
forms much of the PR segment on the ECG. Part of the atrial repolarisation can be
represented by the PR segment (see Fig. 8.3 ).
Propagation from the AV node (A) to the ventricles is provided by a specialised
conduction system. The distal portion of the AV node is composed of a common
bundle called the Bundle of His, shown as landmark node D in Fig. 8.4 (b). The
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