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<DT><A NAME="foot31">...<IMG
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SRC="img6.png"
ALT="$^{2,3}$"></A><A
HREF="index.shtml#tex2html1"><SUP><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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<DD><IMG
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ALT="$^1$">Department of Engineering Science,
University of Oxford, Oxford OX1 3PJ.
<PRE>.
</PRE>
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<DT><A NAME="foot32">...</A><A
HREF="index.shtml#tex2html2"><SUP><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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<DD><IMG
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ALT="$^2$">Mathematical Institute, University of Oxford, Oxford OX1 3LB.
<PRE>.
</PRE>
</DD>
<DT><A NAME="foot33">...</A><A
HREF="index.shtml#tex2html3"><SUP><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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<DD><IMG
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SRC="img8.png"
ALT="$^3$">Centre for the Analysis of Time Series, London School
of Economics, London WC2A 2AE.
<PRE>.
</PRE>
</DD>
<DT><A NAME="foot34">...</A><A
HREF="index.shtml#tex2html4"><SUP><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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<DD>E-mail: mcsharry@robots.ox.ac.uk
<PRE>.
</PRE>
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<TITLE>A dynamical model for generating synthetic electrocardiogram signals</TITLE>
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<H1 ALIGN="CENTER">A dynamical model for generating synthetic electrocardiogram signals</H1>
<P ALIGN="CENTER"><STRONG>Patrick E. McSharry<IMG
WIDTH="21" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img4.png"
ALT="$^{1,2}$">, Gari Clifford<IMG
WIDTH="11" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img5.png"
ALT="$^1$">,
Lionel Tarassenko<IMG
WIDTH="11" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img5.png"
ALT="$^1$"> and Leonard A. Smith<IMG
WIDTH="21" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img6.png"
ALT="$^{2,3}$">
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<center><table bgcolor="lightblue" width="90%">
<tr><td>
<p>
This article originally appeared in <em>IEEE Transactions on Biomedical
Engineering</em>, <b>50</b>(3):289-294; March 2003. Please cite this
publication when referencing this material.
<p>
(C)2002 IEEE. Personal use of this material is permitted. However, permission
to reprint/republish this material for advertising or promotional purposes or
for creating new collective works for resale or redistribution to servers or
lists, or to reuse any copyrighted component of this work in other works must
be obtained from the IEEE. This material is presented to ensure timely
dissemination of scholarly and technical work. Copyright and all rights therein
are retained by authors or by other copyright holders. All persons copying this
information are expected to adhere to the terms and constraints invoked by each
author's copyright. In most cases, these works may not be reposted without the
explicit permission of the copyright holder.
<p>
Software that implements the model described in this paper is freely available
<a href="../">here</a>.
</td></tr>
</table></center>
<H3>Abstract:</H3>
<DIV>
A dynamical model based on three coupled ordinary differential equations
is introduced which is capable of generating realistic synthetic
electrocardiogram (ECG) signals. The operator can specify the mean and
standard deviation of the heart rate, the morphology of the PQRST
cycle and the power spectrum of the RR tachogram.
In particular, both Respiratory Sinus Arrhythmia at the high frequencies
(HF) and Mayer waves at the low frequencies (LF)
together with the LF/HF ratio are incorporated in the model.
Much of the beat-to-beat variation in morphology and timing of the human
ECG, including QT dispersion and R-peak amplitude modulation
are shown to result. This model may be employed to assess biomedical
signal processing techniques which are used to compute clinical statistics
from the ECG.
</DIV>
<P>
<BR>
<IMG
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SRC="img9.png"
ALT="\begin{keywords}
Dynamical model, synthetic ECG, QRS morphology, Respiratory si...
... Heart rate variability, RR tachogram, RR-interval, QT-interval.
\end{keywords}">
<BR>
<BR><HR>
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<LI><A NAME="tex2html18"
HREF="node1.html">Introduction</A>
<LI><A NAME="tex2html19"
HREF="node2.html">ECG morphology</A>
<LI><A NAME="tex2html20"
HREF="node3.html">Heart rate variability</A>
<LI><A NAME="tex2html21"
HREF="node4.html">The dynamical model</A>
<LI><A NAME="tex2html22"
HREF="node5.html">Results</A>
<LI><A NAME="tex2html23"
HREF="node6.html">Conclusions</A>
<LI><A NAME="tex2html24"
HREF="node7.html">Acknowledgements</A>
<LI><A NAME="tex2html25"
HREF="node8.html">Bibliography</A>
<LI><A NAME="tex2html26"
HREF="node9.html">About this document ...</A>
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<H1><A NAME="SECTION00010000000000000000">
Introduction</A>
</H1>
The
electrocardiogram (ECG) is a time-varying signal reflecting the
ionic current flow which causes the cardiac fibres to contract and
subsequently relax.
The surface ECG is obtained by recording the potential difference between
two electrodes placed on the surface of the skin.
A single normal cycle of the ECG represents the successive atrial
depolarisation/repolarisation and ventricular depolarisation/repolarisation
which occurs with every heart beat. These can be approximately associated
with the peaks and troughs of the ECG waveform labelled P,Q,R,S and T as
shown in Fig. <A HREF="node1.html#f:garipqrst">1</A>.
Extracting useful clinical information from the real (noisy) ECG requires
reliable signal processing techniques [<A
HREF="node8.html#goldberger77">1</A>].
These include R-peak detection [<A
HREF="node8.html#pan85">2</A>,<A
HREF="node8.html#kaplan91">3</A>],
QT-interval detection [<A
HREF="node8.html#davey99">4</A>]
and the derivation of heart rate and respiration rate
from the ECG [<A
HREF="node8.html#moody85">5</A>,<A
HREF="node8.html#moody86">6</A>].
The RR-interval is the time between
successive R-peaks, the inverse of this time interval gives the
instantaneous heart rate.
A series of RR-intervals is known as a RR tachogram and variability of
these RR-intervals reveals important information about the physiological state
of the subject [<A
HREF="node8.html#malik95">7</A>].
At present, new biomedical signal processing algorithms are usually evaluated
by applying them to ECGs in a large database such as the Physionet
database [<A
HREF="node8.html#physionet">8</A>].
While this gives the operator an indication of the accuracy of a given
algorithm when applied to real data, it is difficult to infer how the
performance would vary in different clinical settings with a range of
noise levels and sampling frequencies.
Having access to realistic artificial ECG signals may
facilitate this evaluation.
<DIV ALIGN="CENTER"><A NAME="f:garipqrst"></A><A NAME="53"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 1:</STRONG>
Morphology of a mean PQRST-complex of an ECG recorded
from a normal human.</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="279" BORDER="0"
SRC="img10.png"
ALT="\begin{figure}
\centerline{\psfig{file=garipqrst.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
This paper presents a model for generating a synthetic ECG signal with
realistic PQRST morphology and prescribed heart rate dynamics.
The aim of this model is to provide a
standard realistic ECG signal with known characteristics,
which can be generated with specific statistics
such as the mean and standard deviation of the heart rate
and frequency-domain characteristics of heart rate variability (HRV),
such as the LF/HF ratio, defined as the ratio of power between 0.015 and
0.15 Hz and 0.15 and 0.4 Hz in the RR tachogram [<A
HREF="node8.html#malik95">7</A>].
By generating a signal which represents a <I>typical</I> human ECG, this
facilitates a comparison of different signal processing techniques.
A synthetic ECG can be generated with different sampling frequencies and
different noise levels in order to establish the performance of
a given technique. This performance can be presented, for example,
as the number of true positives, false positives, true negatives and false
negatives for each test. Such performance assessment could be used as
a ``standard'' and would enable clinicians to ascertain which biomedical
signal processing techniques were best for a given application.
The layout of this paper is as follows; section <A HREF="node2.html#s:morphology">II</A>
summarises the physiological mechanisms underlying the cardiac cycle and
reviews the morphological variability which is reflected in the ECG signal.
A brief review of HRV is presented in
section <A HREF="node3.html#s:hrv">III</A>. The dynamical model is introduced in
section <A HREF="node4.html#s:model">IV</A> and investigated in section <A HREF="node5.html#s:results">V</A>.
Section <A HREF="node6.html#s:conclusions">VI</A> concludes and discusses extensions to
the model which may be useful for simulating specific disorders.
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<H1><A NAME="SECTION00020000000000000000"></A>
<A NAME="s:morphology"></A>
<BR>
ECG morphology
</H1>
Each beat of the heart can be observed as a series of deflections away from
the baseline on the ECG. These deflections reflect the time
evolution of electrical activity in the heart which initiates
muscle contraction. A single sinus (normal) cycle of the ECG,
corresponding to one
heart beat, is traditionally labelled with the letters P,Q,R,S and T
on each of its turning points (Fig. <A HREF="node1.html#f:garipqrst">1</A>).
The ECG may be divided into the following sections:
<UL>
<LI>P-wave: a small low-voltage deflection away from the baseline
caused by the depolarisation of the atria prior to atrial contraction as the
activation (depolarisation) wave-front propagates
from the SA node through the atria.
<BR>
</LI>
<LI>PQ-interval:
the time between the beginning of atrial
depolarisation and the beginning of ventricular depolarisation.
<BR>
</LI>
<LI>QRS-complex: the largest-amplitude portion of the ECG, caused by
currents generated when the ventricles depolarise prior to their
contraction. Although atrial repolarisation occurs before ventricular
depolarisation, the latter waveform (i.e. the QRS-complex) is of much greater
amplitude and atrial repolarisation is therefore not seen on the ECG.
<BR>
</LI>
<LI>QT-interval: the time between the onset of ventricular
depolarisation and the end of ventricular repolarisation.
Clinical studies have demonstrated that the QT-interval
increases linearly as the RR-interval increases [<A
HREF="node8.html#davey99">4</A>].
Prolonged QT-interval may be associated with delayed ventricular
repolarisation which may cause ventricular tachyarrhythmias
leading to sudden cardiac death [<A
HREF="node8.html#schwartz78">9</A>].
</LI>
<LI>ST-interval: the time between the end of S-wave and the
beginning of T-wave. Significantly elevated or depressed amplitudes away
from the baseline are often associated with cardiac illness.
</LI>
<LI>T-wave: ventricular repolarisation, whereby the cardiac muscle
is prepared for the next cycle of the ECG.
<BR>
</LI>
</UL><HR>
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<H1><A NAME="SECTION00030000000000000000"></A>
<A NAME="s:hrv"></A>
<BR>
Heart rate variability
</H1>
Analysis of variations in the instantaneous heart rate time series
using the beat-to-beat RR-intervals (the RR tachogram) is known as
Heart Rate Variability (HRV) analysis [<A
HREF="node8.html#malik95">7</A>,<A
HREF="node8.html#eursoccard96">10</A>].
HRV analysis has been shown to provide an assessment of cardiovascular
disease [<A
HREF="node8.html#crawford99">11</A>].
The heart rate may be increased by slow acting sympathetic activity
or decreased by fast acting parasympathetic (vagal) activity.
The balance between the effects of the sympathetic and parasympathetic
systems, the two opposite acting branches of the autonomic nervous system,
is referred to as the sympathovagal balance and
is believed to be reflected in the beat-to-beat changes of the
cardiac cycle [<A
HREF="node8.html#malik95">7</A>].
The heart rate is given by the reciprocal of the RR-interval in units
of beats per minute.
Spectral analysis of the RR tachogram is typically used to
estimate the effect of the sympathetic and parasympathetic modulation
of the RR-intervals. The two main frequency bands of interest
are referred to as the Low-Frequency (LF) band (0.04 to 0.15 Hz)
and the High-Frequency (HF) band (0.15 to 0.4 Hz) [<A
HREF="node8.html#eursoccard96">10</A>].
Sympathetic tone is believed to influence the LF component whereas
both sympathetic and parasympathetic activity have an effect on the HF
component [<A
HREF="node8.html#malik95">7</A>]. The ratio of the power contained in
the LF and HF components has been used as a measure of the sympathovagal
balance [<A
HREF="node8.html#malik95">7</A>,<A
HREF="node8.html#eursoccard96">10</A>].
Respiratory Sinus Arrhythmia (RSA) [<A
HREF="node8.html#hales1733">12</A>,<A
HREF="node8.html#ludwig1847">13</A>]
is the name given to the oscillation in the RR tachogram due to
parasympathetic activity which is synchronous with the respiratory cycle.
The RSA oscillation manifests itself as a
peak in the HF band of the spectrum. For example, 15 breaths per minute
corresponds to a 4 second oscillation with a peak in the power spectrum at
0.25 Hz. A second peak is often found in the LF
band of the spectrum at approximately 0.1 Hz. While the cause of this
10 second rhythm is strongly debated, one possible explanation is that it
may be due to baroreflex regulation which creates the so-called
<I>Mayer waves</I> in the blood pressure signal [<A
HREF="node8.html#deboer87">14</A>].
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<H1><A NAME="SECTION00040000000000000000"></A>
<A NAME="s:model"></A>
<BR>
The dynamical model
</H1>
The model generates a trajectory in a three-dimensional state space
with co-ordinates <IMG
WIDTH="56" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img1.png"
ALT="$(x,y,z)$">. Quasi-periodicity of the ECG is reflected
by the movement of the trajectory around an attracting limit cycle of
unit radius in the <IMG
WIDTH="41" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img11.png"
ALT="$(x,y)$">-plane.
Each revolution on this circle corresponds to one RR-interval or heart beat.
Inter-beat variation in the ECG is reproduced using the
motion of the trajectory in the <IMG
WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img12.png"
ALT="$z$">-direction.
Distinct points on the ECG, such as the P,Q,R,S and T are described by
<I>events</I> corresponding to negative and positive attractors/repellors
in the <IMG
WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img12.png"
ALT="$z$">-direction. These events are placed at fixed angles along the
unit circle given by <IMG
WIDTH="22" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img13.png"
ALT="$\theta_P$">, <IMG
WIDTH="22" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img14.png"
ALT="$\theta_Q$">,<IMG
WIDTH="22" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img15.png"
ALT="$\theta_R$">,<IMG
WIDTH="21" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img16.png"
ALT="$\theta_S$"> and
<IMG
WIDTH="22" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.png"
ALT="$\theta_T$"> (see Fig. <A HREF="node4.html#f:pqrst3d">2</A>). When the trajectory
approaches one of these events, it is pushed upwards or downwards
away from the limit cycle, and then as it moves away it is pulled back
towards the limit cycle.
The dynamical equations of motion are given by a set of three ordinary
differential equations
<BR>
<DIV ALIGN="CENTER"><A NAME="e:pqrst"></A>
<!-- MATH
\begin{eqnarray}
{\dot x} &=& \alpha x - \omega y, \nonumber \\
{\dot y} &=& \alpha y + \omega x, \nonumber \\
{\dot z} &=& - \!\!\!\!\!\! \sum_{i \in \{P,Q,R,S,T\}} \!\!\!\!\!\!
a_i \Delta \theta_i
\exp(-\Delta \theta_i^2 / 2 b_i^2) - (z - z_0),
\end{eqnarray}
-->
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<TR VALIGN="MIDDLE"><TD NOWRAP ALIGN="RIGHT"><IMG
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ALT="$\displaystyle {\dot x}$"></TD>
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SRC="img19.png"
ALT="$\textstyle =$"></TD>
<TD ALIGN="LEFT" NOWRAP><IMG
WIDTH="66" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img20.png"
ALT="$\displaystyle \alpha x - \omega y,$"></TD>
<TD WIDTH=10 ALIGN="RIGHT">
&nbsp;</TD></TR>
<TR VALIGN="MIDDLE"><TD NOWRAP ALIGN="RIGHT"><IMG
WIDTH="12" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img21.png"
ALT="$\displaystyle {\dot y}$"></TD>
<TD ALIGN="CENTER" NOWRAP><IMG
WIDTH="16" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img19.png"
ALT="$\textstyle =$"></TD>
<TD ALIGN="LEFT" NOWRAP><IMG
WIDTH="66" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img22.png"
ALT="$\displaystyle \alpha y + \omega x,$"></TD>
<TD WIDTH=10 ALIGN="RIGHT">
&nbsp;</TD></TR>
<TR VALIGN="MIDDLE"><TD NOWRAP ALIGN="RIGHT"><IMG
WIDTH="12" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img23.png"
ALT="$\displaystyle {\dot z}$"></TD>
<TD ALIGN="CENTER" NOWRAP><IMG
WIDTH="16" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img19.png"
ALT="$\textstyle =$"></TD>
<TD ALIGN="LEFT" NOWRAP><IMG
WIDTH="304" HEIGHT="56" ALIGN="MIDDLE" BORDER="0"
SRC="img24.png"
ALT="$\displaystyle - \!\!\!\!\!\! \sum_{i \in \{P,Q,R,S,T\}} \!\!\!\!\!\!
a_i \Delta \theta_i
\exp(-\Delta \theta_i^2 / 2 b_i^2) - (z - z_0),$"></TD>
<TD WIDTH=10 ALIGN="RIGHT">
(1)</TD></TR>
</TABLE></DIV>
<BR CLEAR="ALL"><P></P>
where <!-- MATH
$\alpha = 1 - \sqrt{x^2 + y^2}$
-->
<IMG
WIDTH="130" HEIGHT="38" ALIGN="MIDDLE" BORDER="0"
SRC="img25.png"
ALT="$\alpha = 1 - \sqrt{x^2 + y^2}$">,
<!-- MATH
$\Delta \theta_i = (\theta - \theta_i) \ {\rm mod} \ 2 \pi$
-->
<IMG
WIDTH="163" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img26.png"
ALT="$\Delta \theta_i = (\theta - \theta_i) \ {\rm mod} \ 2 \pi$">,
<!-- MATH
$\theta = {\rm atan2}(y,x)$
-->
<IMG
WIDTH="109" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img27.png"
ALT="$\theta = {\rm atan2}(y,x)$"> and <IMG
WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img28.png"
ALT="$\omega$"> is the angular velocity
of the trajectory as it moves around the limit cycle.
Baseline wander was introduced by coupling the baseline value <IMG
WIDTH="19" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img29.png"
ALT="$z_0$">
in (<A HREF="node4.html#e:pqrst">1</A>) to the respiratory frequency <IMG
WIDTH="19" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img30.png"
ALT="$f_2$"> using
<BR>
<DIV ALIGN="RIGHT">
<!-- MATH
\begin{equation}
z_0(t) = A \sin(2 \pi f_2 t),
\end{equation}
-->
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="e:baseline"></A><IMG
WIDTH="142" HEIGHT="28" BORDER="0"
SRC="img31.png"
ALT="\begin{displaymath}
z_0(t) = A \sin(2 \pi f_2 t),
\end{displaymath}"></TD>
<TD WIDTH=10 ALIGN="RIGHT">
(2)</TD></TR>
</TABLE>
<BR CLEAR="ALL"></DIV><P></P>
where <IMG
WIDTH="66" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img32.png"
ALT="$A = 0.15$"> mV.
These equations of motion given by (<A HREF="node4.html#e:pqrst">1</A>) were integrated
numerically using a fourth order
Runge-Kutta method [<A
HREF="node8.html#press92">15</A>] with a fixed time step <!-- MATH
$\Delta t = 1/f_s$
-->
<IMG
WIDTH="75" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img33.png"
ALT="$\Delta t = 1/f_s$">
where <IMG
WIDTH="19" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img34.png"
ALT="$f_s$"> is the sampling frequency.
Visual analysis of a section of typical ECG from a normal subject
was used to suggest suitable times (and therefore angles <IMG
WIDTH="17" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img35.png"
ALT="$\theta_i$">)
and values of <IMG
WIDTH="18" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img36.png"
ALT="$a_i$"> and <IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img37.png"
ALT="$b_i$"> for the PQRST points.
The times and angles are specified relative to
the position of the R-peak as shown in Table <A HREF="node4.html#t:pqrst">I</A>.
A trajectory generated by equation (<A HREF="node4.html#e:pqrst">1</A>) in three-dimensions
corresponding to <IMG
WIDTH="56" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img1.png"
ALT="$(x,y,z)$"> is illustrated in Fig. <A HREF="node4.html#f:pqrst3d">2</A>.
This demonstrates how the
positions of the events <IMG
WIDTH="89" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.png"
ALT="$P,Q,R,S,T$"> act on the trajectory in the
<IMG
WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img12.png"
ALT="$z$">-direction as it precesses around the unit circle in the <IMG
WIDTH="41" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img11.png"
ALT="$(x,y)$">-plane.
The <IMG
WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img12.png"
ALT="$z$"> variable from the three-dimensional system (<A HREF="node4.html#e:pqrst">1</A>)
yields a synthetic ECG with realistic PQRST morphology
(Fig. <A HREF="node4.html#f:pqrstcomplex">3</A>). The similarity between the synthetic
ECG and the real ECG may be seen by comparing Fig. <A HREF="node4.html#f:pqrstcomplex">3</A>
with Fig. <A HREF="node1.html#f:garipqrst">1</A>. Note that noise has not been added
to the model at this point.
<BR><P></P>
<DIV ALIGN="CENTER">
<DIV ALIGN="CENTER">
<A NAME="286"></A>
<TABLE CELLPADDING=3 BORDER="1">
<CAPTION><STRONG>Table I:</STRONG>
Parameters of the ECG model given by (<A HREF="node4.html#e:pqrst">1</A>)</CAPTION>
<TR><TD ALIGN="LEFT">Index (i)</TD>
<TD ALIGN="LEFT">P</TD>
<TD ALIGN="LEFT">Q</TD>
<TD ALIGN="LEFT">R</TD>
<TD ALIGN="LEFT">S</TD>
<TD ALIGN="LEFT">T</TD>
</TR>
<TR><TD ALIGN="LEFT">Time (secs)</TD>
<TD ALIGN="LEFT">-0.2</TD>
<TD ALIGN="LEFT">-0.05</TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT">0.05</TD>
<TD ALIGN="LEFT">0.3</TD>
</TR>
<TR><TD ALIGN="LEFT"><IMG
WIDTH="17" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img35.png"
ALT="$\theta_i$"> (radians)</TD>
<TD ALIGN="LEFT"><!-- MATH
$-\frac{1}{3}\pi$
-->
<IMG
WIDTH="36" HEIGHT="34" ALIGN="MIDDLE" BORDER="0"
SRC="img39.png"
ALT="$-\frac{1}{3}\pi$"></TD>
<TD ALIGN="LEFT"><!-- MATH
$-\frac{1}{12}\pi$
-->
<IMG
WIDTH="43" HEIGHT="34" ALIGN="MIDDLE" BORDER="0"
SRC="img40.png"
ALT="$-\frac{1}{12}\pi$"></TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT"><!-- MATH
$\frac{1}{12}\pi$
-->
<IMG
WIDTH="30" HEIGHT="34" ALIGN="MIDDLE" BORDER="0"
SRC="img41.png"
ALT="$\frac{1}{12}\pi$"></TD>
<TD ALIGN="LEFT"><!-- MATH
$\frac{1}{2}\pi$
-->
<IMG
WIDTH="24" HEIGHT="34" ALIGN="MIDDLE" BORDER="0"
SRC="img42.png"
ALT="$\frac{1}{2}\pi$"></TD>
</TR>
<TR><TD ALIGN="LEFT"><IMG
WIDTH="18" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img36.png"
ALT="$a_i$"></TD>
<TD ALIGN="LEFT">1.2</TD>
<TD ALIGN="LEFT">-5.0</TD>
<TD ALIGN="LEFT">30.0</TD>
<TD ALIGN="LEFT">-7.5</TD>
<TD ALIGN="LEFT">0.75</TD>
</TR>
<TR><TD ALIGN="LEFT"><IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img37.png"
ALT="$b_i$"></TD>
<TD ALIGN="LEFT">0.25</TD>
<TD ALIGN="LEFT">0.1</TD>
<TD ALIGN="LEFT">0.1</TD>
<TD ALIGN="LEFT">0.1</TD>
<TD ALIGN="LEFT">0.4</TD>
</TR>
</TABLE>
<A NAME="t:pqrst"></A>
</DIV>
</DIV>
<BR>
<DIV ALIGN="CENTER"><A NAME="f:pqrst3d"></A><A NAME="288"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 2:</STRONG>
A typical trajectory generated by the dynamical model
(<A HREF="node4.html#e:pqrst">1</A>) in the three-dimensional space given by <IMG
WIDTH="56" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img1.png"
ALT="$(x,y,z)$">. The dashed
line reflects the limit cycle of unit radius while the small circles show the
positions of the P,Q,R,S,T events.</CAPTION>
<TR><TD><IMG
WIDTH="351" HEIGHT="271" BORDER="0"
SRC="img43.png"
ALT="\begin{figure}
\centerline{\psfig{file=pqrst3d.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
<DIV ALIGN="CENTER"><A NAME="f:pqrstcomplex"></A><A NAME="128"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 3:</STRONG>
Morphology of one PQRST-complex of the ECG.</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="275" BORDER="0"
SRC="img44.png"
ALT="\begin{figure}
\centerline{\psfig{file=pqrstcomplex.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
By contrasting the dynamical model (<A HREF="node4.html#e:pqrst">1</A>) with the mechanisms
underlying the cardiac cycle, it is obvious that the time required to
complete one lap of the limit cycle is equal to the RR-interval
of the synthetic ECG signal. Variations in the length of the RR-intervals
can be incorporated by varying the angular velocity <IMG
WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img28.png"
ALT="$\omega$">.
The effects of both RSA and Mayer waves in the power spectrum
<IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$"> of the RR-intervals are incorporated
by generating RR-intervals which have a bimodal power spectrum
consisting of the sum of two Gaussian distributions,
<BR>
<DIV ALIGN="RIGHT">
<!-- MATH
\begin{equation}
S(f) = \frac{\sigma_1^2}{\sqrt{2 \pi c_1^2}}
\exp \left( \frac{(f - f_1)^2}{2 c_1^2} \right)
+ \frac{\sigma_2^2}{\sqrt{2 \pi c_2^2}}
\exp \left( \frac{(f - f_2)^2}{2 c_2^2} \right),
\end{equation}
-->
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="e:Sf"></A><IMG
WIDTH="423" HEIGHT="48" BORDER="0"
SRC="img45.png"
ALT="\begin{displaymath}
S(f) = \frac{\sigma_1^2}{\sqrt{2 \pi c_1^2}}
\exp \left( ...
...c_2^2}}
\exp \left( \frac{(f - f_2)^2}{2 c_2^2} \right),
\end{displaymath}"></TD>
<TD WIDTH=10 ALIGN="RIGHT">
(3)</TD></TR>
</TABLE>
<BR CLEAR="ALL"></DIV><P></P>
with means <IMG
WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img46.png"
ALT="$f_1,f_2$"> and standard
deviations <IMG
WIDTH="39" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img47.png"
ALT="$c_1,c_2$">. Power in the LF and HF bands are given by
<IMG
WIDTH="21" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
SRC="img48.png"
ALT="$\sigma_1^2$"> and <IMG
WIDTH="21" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
SRC="img49.png"
ALT="$\sigma_2^2$"> respectively whereas the variance
equals the total area <!-- MATH
$\sigma^2 = \sigma^2_1+\sigma^2_2$
-->
<IMG
WIDTH="95" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
SRC="img50.png"
ALT="$\sigma^2 = \sigma^2_1+\sigma^2_2$">,
yielding an LF/HF ratio of <!-- MATH
$\sigma^2_1/\sigma^2_2$
-->
<IMG
WIDTH="46" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
SRC="img51.png"
ALT="$\sigma^2_1/\sigma^2_2$">.
Fig. <A HREF="node4.html#f:Sf">4</A> shows the power spectrum <IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$"> given
by <IMG
WIDTH="61" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img52.png"
ALT="$f_1 = 0.1$">,
<IMG
WIDTH="69" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img53.png"
ALT="$f_2 = 0.25$">, <IMG
WIDTH="68" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img54.png"
ALT="$c_1 = 0.01$">, <IMG
WIDTH="68" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="img55.png"
ALT="$c_2 = 0.01$"> and <!-- MATH
$\sigma^2_1/\sigma^2_2 = 0.5$
-->
<IMG
WIDTH="87" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
SRC="img56.png"
ALT="$\sigma^2_1/\sigma^2_2 = 0.5$">.
The Gaussian frequency distribution is motivated by the
typical power spectrum of a real RR tachogram [<A
HREF="node8.html#malik95">7</A>].
<DIV ALIGN="CENTER"><A NAME="f:Sf"></A><A NAME="145"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4:</STRONG>
Power spectrum <IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$"> of the RR-interval process
with a LF/HF ratio of <!-- MATH
$\sigma_1^2/\sigma_2^2 = 0.5$
-->
<IMG
WIDTH="87" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
SRC="img3.png"
ALT="$\sigma _1^2/\sigma _2^2 = 0.5$">.</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="275" BORDER="0"
SRC="img57.png"
ALT="\begin{figure}
\centerline{\psfig{file=Sf.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
A RR-interval time series <IMG
WIDTH="34" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img58.png"
ALT="$T(t)$"> with power spectrum <IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$"> is generated by
taking the inverse Fourier transform of a sequence of complex numbers with
amplitudes <IMG
WIDTH="53" HEIGHT="37" ALIGN="MIDDLE" BORDER="0"
SRC="img59.png"
ALT="$\sqrt{S(f)}$"> and phases which are randomly
distributed between 0 and <IMG
WIDTH="22" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img60.png"
ALT="$2 \pi$">.
By multiplying this time series by an appropriate
scaling constant and adding an offset value, the resulting time series can be
given any required mean and standard deviation.
Suppose that <IMG
WIDTH="34" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img58.png"
ALT="$T(t)$"> represents the time series generated by the RR-process
with power spectrum <IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$">. The time-dependent
angular velocity <IMG
WIDTH="33" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img61.png"
ALT="$\omega(t)$"> of motion around the limit cycle is then given
by
<BR>
<DIV ALIGN="RIGHT">
<!-- MATH
\begin{equation}
\omega(t) = \frac{2 \pi}{T(t)}.
\end{equation}
-->
<TABLE WIDTH="100%" ALIGN="CENTER">
<TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><IMG
WIDTH="88" HEIGHT="42" BORDER="0"
SRC="img62.png"
ALT="\begin{displaymath}
\omega(t) = \frac{2 \pi}{T(t)}.
\end{displaymath}"></TD>
<TD WIDTH=10 ALIGN="RIGHT">
(4)</TD></TR>
</TABLE>
<BR CLEAR="ALL"></DIV><P></P>
In this way the series of RR-intervals of the resultant
synthetic ECG will also have a power spectrum equal to <IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$">; this will be
demonstrated in the next section.
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<H1><A NAME="SECTION00050000000000000000"></A>
<A NAME="s:results"></A>
<BR>
Results
</H1>
The synthetic ECG (Fig. <A HREF="node5.html#f:ecgsynthetic">5</A>) illustrates
the modulation of the QRS-complex due to RSA.
Observational uncertainty is incorporated by adding normally
distributed measurement errors with mean zero
and standard deviation 0.025 mV (Fig. <A HREF="node5.html#f:ecgcomparison">6</A>a),
yielding a similar signal to a segment of real ECG from a normal human
(Fig. <A HREF="node5.html#f:ecgcomparison">6</A>b).
In order to illustrate the
dynamics of the RR-intervals obtained from this synthetic ECG, peak detection
was used to identify the times of the R-peaks.
In the noise-free case, a simple algorithm which looks for local maxima
within a small window is sufficient. For ECGs with noise and artefacts it
may be necessary to use more complicated methods [<A
HREF="node8.html#pan85">2</A>,<A
HREF="node8.html#kaplan91">3</A>].
A comparison between the continuous process with power spectrum <IMG
WIDTH="37" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img2.png"
ALT="$S(f)$">
given by (<A HREF="node4.html#e:Sf">3</A>) and the piecewise constant
reconstruction of the RR-process obtained from the R-peak detection
(Fig. <A HREF="node5.html#f:rrinout">7</A>) illustrates the measurement errors that
arise when computing heart rate variability statistics from
RR-intervals.
The RR-intervals (Fig. <A HREF="node5.html#f:rrsynthetic">8</A>a) and corresponding
instantaneous heart rate (Fig. <A HREF="node5.html#f:rrsynthetic">8</A>b)
in units of beats per minute (bpm)
for a mean of 60 bpm and standard deviation of 5 bpm
display variability due to both RSA and Mayer waves.
A spectral estimation technique
for unevenly sampled time series, the Lomb periodogram
[<A
HREF="node8.html#press92">15</A>,<A
HREF="node8.html#laguna98">16</A>], was used to calculate the power
spectrum (Fig. <A HREF="node5.html#f:rrsynthetic">8</A>c) from the RR tachogram,
derived from 5 minutes of data as recommended
by [<A
HREF="node8.html#malik95">7</A>,<A
HREF="node8.html#eursoccard96">10</A>].
Despite the loss of information in going from the continuous process to the
piecewise constant reconstruction, a comparison between Fig. <A HREF="node4.html#f:Sf">4</A> and
Fig. <A HREF="node5.html#f:rrsynthetic">8</A>c illustrates that it is still
possible to obtain a reasonable estimate of the power spectrum.
<DIV ALIGN="CENTER"><A NAME="f:ecgsynthetic"></A><A NAME="168"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5:</STRONG>
ECG generated by dynamical model: (a) 10 seconds and (b) 50 seconds.</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="275" BORDER="0"
SRC="img63.png"
ALT="\begin{figure}
\centerline{\psfig{file=ecgsynthetic.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
<DIV ALIGN="CENTER"><A NAME="f:ecgcomparison"></A><A NAME="173"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 6:</STRONG>
Comparison between (a) synthetic ECG with additive normally
distributed measurement errors and (b) real ECG signal from a normal human.</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="275" BORDER="0"
SRC="img64.png"
ALT="\begin{figure}
\centerline{\psfig{file=ecgcomparison.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
<DIV ALIGN="CENTER"><A NAME="f:rrinout"></A><A NAME="296"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 7:</STRONG>
Reconstruction of RR-process from R-peak detection:
the underlying RR-process generated using (<A HREF="node4.html#e:Sf">3</A>) (black line)
and the RR-interval time series obtained using R-peak
detection of the synthetic ECG (grey line).</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="275" BORDER="0"
SRC="img65.png"
ALT="\begin{figure}
\centerline{\psfig{file=rrinout.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
<DIV ALIGN="CENTER"><A NAME="f:rrsynthetic"></A><A NAME="298"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 8:</STRONG>
Analysis of RR-intervals from R-peak detection of the ECG signal
generated by the dynamical model (<A HREF="node4.html#e:pqrst">1</A>) with mean heart rate 60 bpm
and standard deviation 5 bpm: (a) RR-intervals,
(b) instantaneous heart rate and (c) power spectrum of the RR-intervals.
Note the two active frequencies belonging to RSA (0.25 Hz) and Mayer
waves (0.1 Hz).</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="272" BORDER="0"
SRC="img66.png"
ALT="\begin{figure}
\centerline{\psfig{file=rrsynthetic.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
An increase in the RR-interval implies that the trajectory has more time to
get pushed into the peak and trough given by the R and S events.
This is reflected by the strong correlation between the RR-intervals and the
RS-amplitude as shown in Fig. <A HREF="node5.html#f:rsrr">9</A>. A technique for deriving a measure
of the rate of respiration
from the ECG has been proposed [<A
HREF="node8.html#moody85">5</A>,<A
HREF="node8.html#moody86">6</A>].
This ECG-derived respiratory signal (EDR) is of clinical use in
situations where the ECG, but not respiration, is recorded.
The synthetic ECG provides a means of testing the robustness of such
techniques against noise and the effects of different sampling frequencies.
<DIV ALIGN="CENTER"><A NAME="f:rsrr"></A><A NAME="190"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 9:</STRONG>
RS-amplitudes versus RR-intervals for the synthetic ECG.</CAPTION>
<TR><TD><IMG
WIDTH="351" HEIGHT="275" BORDER="0"
SRC="img67.png"
ALT="\begin{figure}
\centerline{\psfig{file=rsrr.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
As a consequence of constructing the model with a variable angular frequency
<IMG
WIDTH="33" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img61.png"
ALT="$\omega(t)$">, the time taken to
move from the Q event to the T event, known as the QT-interval, varies with
the RR-interval on a beat-to-beat basis.
The relationship between the QT-interval and the
RR-interval is linear as shown in Fig. <A HREF="node5.html#f:qtrr">10</A>.
Such a linear relationship has been reported for real ECGs and
has been used to calculate a corrected QT-interval [<A
HREF="node8.html#davey99">4</A>].
It is interesting that this relationship is a direct consequence of the
model. Furthermore it may be possible to use the model to assess how much of
the variation in the QT-interval is due to RR-interval variability so that
this effect can be factored out.
<DIV ALIGN="CENTER"><A NAME="f:qtrr"></A><A NAME="197"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 10:</STRONG>
QT-intervals versus RR-intervals for the synthetic ECG.</CAPTION>
<TR><TD><IMG
WIDTH="352" HEIGHT="275" BORDER="0"
SRC="img68.png"
ALT="\begin{figure}
\centerline{\psfig{file=qtrr.eps,width=7.75cm}}
\end{figure}"></TD></TR>
</TABLE>
</DIV>
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<H1><A NAME="SECTION00060000000000000000"></A>
<A NAME="s:conclusions"></A>
<BR>
Conclusions
</H1>
A new dynamical model has been introduced which is capable of replicating
many of the important features of the human ECG.
Moreover, many of the morphological changes observed in the human ECG
manifest as a consequence of the geometrical structure of the model.
Model parameters may be
chosen to generate different morphologies for the PQRST-complex.
The power spectrum of the RR-intervals can be selected <I>a priori</I> and used
to drive the ECG generator. This allows the operator to prescribe specific
characteristics of the heart rate dynamics such as the mean and standard
deviation of the heart rate and
spectral properties such as the LF/HF ratio.
In addition the average morphology can be controlled by specifying the
positions of the P,Q,R,S and T events and the magnitude of their effect
on the ECG.
Having access to a realistic ECG provides a benchmark for testing
numerous biomedical signal processing techniques. In order to establish
the operational properties of these techniques in a clinical setting,
it is important to know
how they perform for different noise levels and sampling frequencies.
A number of applications and simple extensions of the model are possible:
(i) By fitting (see [<A
HREF="node8.html#mcsharry99a">17</A>]) the model
to the morphology of a particular subject's ECG
and the power spectrum of their RR-intervals,
a database of realistic ECGs could be created.
This database could be employed for statistical hypothesis testing.
Furthermore, it may be possible derive a corrected QT-interval which is
independent of the heart rate.
(ii) The synthetic ECG could be used to assess the effectiveness of
different techniques for noise and artefact removal.
These could be evaluated by adding noise and/or artefact onto the
synthetic signal and then comparing the original with the processed signal.
(iii) Abnormal morphological changes with time could be introduced
by using a parameter to control the position of any of the P,Q,R,S or T events.
This extension would be particularly useful for testing techniques
which aim to detect ST depression or elevation by decreasing or
increasing the <IMG
WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img12.png"
ALT="$z$">-position of the T wave over time.
Similarly QT prolongation could be replicated by moving the T point away
from the Q point in the <IMG
WIDTH="41" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img11.png"
ALT="$(x,y)$"> plane (increasing
<!-- MATH
$\theta_T - \theta_Q$
-->
<IMG
WIDTH="59" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img69.png"
ALT="$\theta_T - \theta_Q$">).
(iv) The model could be used to produce multi-lead ECG signals by
introducing a measurement function which maps from the
<IMG
WIDTH="56" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img1.png"
ALT="$(x,y,z)$"> model space to the ECG signal: <IMG
WIDTH="94" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
SRC="img70.png"
ALT="$s = h(x,y,z)$">. Different lead
configurations and modulations due to respiration and movement of the
cardiac axis could be modelled using time-dependent functions for <IMG
WIDTH="13" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img71.png"
ALT="$h$">.
(v) Abnormal beats, such as ectopics, can be simulated by
modifying the position of the R-peak for one cycle of the dynamics.
The new model presented here reflects a data-driven approach to modelling the
electrical activity of the heart. Key physiological features have been
incorporated using motion of a trajectory throughout a three-dimensional state
space. The quasi-periodicity of the cardiac cycle is represented by
attraction towards a limit cycle.
The model produces QT-intervals and R-peak height variation (RSA)
which vary linearly with the RR-intervals
as has been found in real ECGs [<A
HREF="node8.html#moody86">6</A>,<A
HREF="node8.html#davey99">4</A>].
It is hoped that this model will provide a valuable tool
for testing biomedical signal processing algorithms applied to ECG signals
with different sampling frequencies and
levels of noise and/or movement artefact.
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<H1><A NAME="SECTION00070000000000000000">
Acknowledgements</A>
</H1>
This research was supported by EPSRC grant GR/N02641 and Oxford BioSignals.
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<H2><A NAME="SECTION00080000000000000000">
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<IMG
WIDTH="553" HEIGHT="148" ALIGN="BOTTOM" BORDER="0"
SRC="img72.png"
ALT="\begin{biography}{Patrick E. McSharry} was born in Leitrim, Ireland in 1972.
H...
...cal modelling,
forecasting and biomedical signal processing.
\end{biography}">
<BR>
<BR>
<IMG
WIDTH="554" HEIGHT="148" ALIGN="BOTTOM" BORDER="0"
SRC="img73.png"
ALT="\begin{biography}{Gari D. Clifford}
was born in Alton, Hampshire, UK in 1971.
...
...sis, biomedical signal processing
and mathematical modelling.
\end{biography}">
<BR>
<BR>
<IMG
WIDTH="556" HEIGHT="208" ALIGN="BOTTOM" BORDER="0"
SRC="img74.png"
ALT="\begin{biography}{Lionel Tarassenko} MA, DPhil, FREng, FIEE was born in
Paris ...
...d
to a Fellowship of the Royal Academy of Engineering in 2000.
\end{biography}">
<BR>
<BR>
<IMG
WIDTH="554" HEIGHT="152" ALIGN="BOTTOM" BORDER="0"
SRC="img75.png"
ALT="\begin{biography}{Leonard A. Smith} received a BS in Physics,
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... the definition of noise; and nonlinear time series
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\end{biography}">
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<STRONG>A dynamical model for generating synthetic electrocardiogram signals</STRONG><P>
This document was generated using the
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Copyright &#169; 1993, 1994, 1995, 1996,
<A HREF="http://cbl.leeds.ac.uk/nikos/personal.html">Nikos Drakos</A>,
Computer Based Learning Unit, University of Leeds.
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Copyright &#169; 1997, 1998, 1999,
<A HREF="http://www.maths.mq.edu.au/~ross/">Ross Moore</A>,
Mathematics Department, Macquarie University, Sydney.
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