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Some Ideas for Visualizing Cardiac Sounds
Since 1997apr03, I've been talking (emailing) with Joan Freedman and W. Reid
Thompson about the possibility of a tool for visualizing cardiac sounds, to aid
students in learning to recognize and distinguish features of those sounds.
I've created this document as a place to collect, summarize, and share some
ideas about such a tool.
To the extent that I can, I will say where these ideas came from. Please let me
know if anything I've written here is unclear. And most important: if there's
something you think I should add, please tell me!
1997apr03 It was Joan Freedman's idea that a display along the lines of the
Music Animation Machine could be used to highlight the differences in
heart sounds, and thus teach pediatricians to distinguish normal heart sounds
from abnormal ones. I told her that although the Music Animation Machine
display itself wasn't suitable, some sort of special-purpose sonogram (such
a tool designed for visualizing the singing voice) could be invented.
1997apr04 I suggested having visual artists listen to heart sounds and draw
pictures of what they heard, as a way to generate useful analogies
between aural and visual patterns. I also suggested doing an AI neural network
sort of approach, having a neural net trained by expert cardiologists.
Since the heartbeat is a cyclic pattern, it might be useful to have a
visualization which reflected this, which used a circular, rather than linear,
representation of time. In this way, changes between cycles of the
heartbeat would become animations of a single object (at the same approximate
position in the display); changes in heartrate would appear as displacements
around the circle, etc. Some sketches for this are here.
Later (1997apr09) I had the idea of an "average" heartbeat accumulating in this
picture (either by actually averaging the data from multiple cycles, or by just
drawing one cycle on top of another).
1997apr09 W. Reid Thompson explained that his project was twofold: a) to make a
web-based teaching module, and b) to collect a database of normal and abnormal
cardiac recordings to aid in the search for recognizable differences
that could be incorporated into an automated diagnostic screening tool.
1997apr09 After listening to some sample cardiac sounds, I realized that
differences between one recording and another could be caused by many factors
that had little or nothing to do with the heart's functioning (e.g. the
microphone, fatty tissues between the heart and the microphone, etc.), and that something
akin to a stereo system's "graphic equalizer" would be useful for removing
insignificant differences. A related idea was to somehow calibrate this
by applying a known sound to the patient's body. 1997apr11, Reid
pointed out that the diagnostician's hearing was also a factor, and that we need
a way to calibrate that.
1997apr09 Animations of the heart. Currently, there are sonograms (and x-rays?)
of the heart; an addition to this would be an animated schematic picture of the
heart, showing the parts that are different when there is an
abnormality. 1997apr10, Reid said he was planning to include motion video from
sonograms. I started thinking about how we go from a sound to the idea
of the object or action that produced that sound, and wondered whether a
schematic (animation) could serve as an intermediate point between the sounds
of the heart and the structures/events which created them. Reid pointed
out that infant heart sounds presented special problems, because the
faster beatrate could be misleading.
The sound of a heartbeat is the final result of a chain of things:
electrical impulses result in muscle tension, which results in motion of
muscles and other tissues, leading to blood flow (and turbulence), valves
closing, etc.; these sounds are (selectively) absorbed as they pass through
tissue. Differences at each stage can contribute to differences in the final
sound. How could this chain of cause and effect be represented (and
viewed) in the visualization of the sound? One possible way is to look at not
just the final waveform, but various transformations of it (more description
and pictures here).
Various attributes of a sound, once extracted algorithmically, could be
presented visually in different ways (also discussed and diagrammed
"Compared to what?" is a useful question; with a heartbeat, the usual answer is "compared
to a normal heartbeat." So, we could have a display which showed not
just the waveform (or some transformation of it), but the differences between
the patient's waveform and a normal one (discussed and pictured
1997apr11 Reid explained that there was a typical way for the rhythm of the
heartbeat to change when the period changed. It might be useful to have
something which made it obvious when changes did not fit the typical pattern.
1997apr11 A fundamental principle for a diagnostic tool: the diagnostician
using the tool needs to understand what the tool does. This means that even if a
tool is technically complex, it should be conceptually simple.
1997apr11 A heartbeat synthesizer could be useful in several ways:
A related idea is a tool which allows a "morph" between two sounds: a
way to create a waveform which is an interpolation point between two sounds.
This could be used to create a small amount of a certain feature, to sensitize
a student to it.
Just in designing and refining it, you'd have to
develop a systematic way of thinking about heart sounds; you'd have to build a
model that could account for all the typical variations. This model might
suggest ways of describing the sounds that wouldn't occur to you normally.
You could use it to probe the expertise of cardiac
authorities. A researcher could change various parameters, and the expert
would say, at a certain point, "okay, now it's sounding a little less like
____ and a little more like ____." If you were trying to build an AI-style
expert system, this kind of probing could be very useful.
For teaching, it could be used to generate samples of
conditions which meet certain otherwise hard-to-find criteria (for example, a
really subtle example of a certain condition, or two conditions at the same
time, or something which is never heard).
As an exercise, a student could be given some samples (taken from real
patients) and told, "synthesize heart sounds which sound the same." This would
train them to hear the differences better. (As well I know, having done
analogous things in music; once you have the responsibility for control of something, you
become much more aware of it's nature!)
And of course, it could be used as part of a teaching module, to generate a
variety of heart sounds without having to store samples. (The downside to this
is that they aren't real, and might be misleading)
1997may04 We haven't said this explicitly anywhere, though we're assuming it: use
FFTs and related tools for extraction of features of the heartbeat.
2005sep19 Eldon Nelson read this page and took the idea as the subject of a thesis for his Biosystems Instrumentation class.
2005dec19 Eldon Nelson (tenthousandfailures.com) posted Investigations into Visualization and Significance of Phase Relationships in Cardiac Rhythms
Last update 2006mar16.