5.0 Analysis
5.1 Introduction:
All twelve subjects successfully completed full analysis sessions lasting
approximately 45 minuets with no adverse effects. Each session consisted of a
familiarisation period, a free breathing analysis session and then the audio and
visual training / feed-back sessions. Each session was conducted in a quiet, preprepared room specifically set up for the measurements – see chapter 4 –
experimental method.
5.2 Free Breathing and the ubiquitous sine-wave formulation
It has been common practice for several years and advocated by several
research groups, to replicate a patient’s breathing pattern using a single
compartment model.
Such a model, described by Bloes et al,
results in a
formalism that describes the breathing displacement time graph using a single
sine wave with a fixed period and amplitude. Unfortunately all the evidence in
the literature points to anything but such a model. Shown if figures ?? and XX
are samples of free breathing patterns from two subjects measured during this
work. The individual traces correspond to isolated inhale-exhale cycles (of which
we are showing seven in each plot for brevity). What is clearly evident is that the
amplitude, the position of maximal inhalation (corresponding to the phase) and
the period vary from cycle to cycle. The effect is subject dependent as can be
seen by comparing figures ?? and XX.
In figure ?? the variation in all parameters is quite pronounced – for example the
peaks of the green and black plots (peaks marked as B and A respectively)
occur at quite different times - approximately 54.2 seconds and 55 seconds
respectively. The subject shown in figure XX, exhibits a more tightly controlled
breathing pattern. This variation in period, amplitude and phase appears both
across cycles for a single subject and also across subjects - for all subjects
studied in this work. Clearly then it is inappropriate to fit a single compartment
model in which the parameters are purely deterministic to such data in order to
analyse the effects of different feedback protocols on the breathing patterns of
subjects. In this chapter we use the methods discussed in chapter XXX(theory)
to analyse the results.
220
A - peak of black plot
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Displacement
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B - peak of green plot
100
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Time Sec
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57.5
Figure ??; The figure shows the variation in free-breathing pattern for subject 1.
Each curve represents a measured inhalation-exhalation cycle. In this figure,
seven cycles are shown. Clearly the shape, period and location of maximum
changes from cycle to cycle as does the mean breathing level. That the phase is
changing is seen by the times at which the peaks marked A and B occur.
110
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Displacement
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Time Sec
Figure XX:The figure shows the variation in free-breathing pattern for subject 2.
Each curve represents a measured inhalation-exhalation cycle. Seven cycles
are shown. Here the location of the maxima, the mean level and the period are
more consistent from cycle-to-cycle in comparison with that of subject 1 – figure
??
Figures aa – dd demonstrate the effects of video feed-back on the breathing
pattern of a subject – the kernel of this thesis. Figure aa shows that during the
free breathing session the subject continuously modified their mean breathing
position, as seen by the positive slope to the mean breathing depth (dotted arrow
in the figure). This corresponds to the subject not completely exhaling. Also
seen are non-periodic changes in the overall local shape of the graph with some
large excursions in breath – presumably to compensate for the slowly increasing
lack of lung emptying. Figure bb is the breathing pattern from the same subject
as in aa but this time the subject is attempting to follow a visually presented
synthetic breathing pattern. The synthetic pattern is a simple sinusoid with a
period equal to the average period of the subject’s free breathing trace and
amplitude equal to the mean amplitude from the free-breathing trace. Clearly
evident in figure bb is the now stable mean breathing position as compared with
the free-breathing case. Also, the amplitude appears to be much more stable
throughout the measurement period. Figure cc shows a short-time window of the
data in bb. We can see quite clearly that the subject is matching quite well the
period and phase of the training signal – shown in black. That this consistency
continues over the whole of the measurement period can be seen in figure dd –
this is figure aa but with the training waveform included.
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Relative displacement
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0
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Time Sec
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Fig: aa Free breathing trace for subject 2. The subject had no training, notice the
irregularity in the breathing pattern, the changing mean breathing depth
(corresponding to a change in the subject’s mean chest position at exhale.(sal) –
and shown by the dotted arrow-line.
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Relative Displacement
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0
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Time Sec
Fig: bb Video trained breathing trace for subject 2 – the training signal has been
removed for clarity. Notice how the breathing pattern doesn’t show the mean
breathing depth drift present in the free breathing trace Figure aa).
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Amplitudes
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0
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Time Sec
Fig: cc Video trained breathing trace (blue) for subject B –including the training pattern
(black) – for clarity we have limited the time axis to 80 seconds but the pattern persists
beyond this – see figure dd. We can see that the subject is matching the peaks-and
troughs of the training signal (breathing period and phase) very well. Also the amplitude
(depth of breathing) is remaining relatively constant.
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Relative Displacement
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130
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90
70
0
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Time Sec
Fig: dd Video trained breathing trace (Blue) for subject 2 –including the training
pattern (Black) for the whole measurement period. Consistency is maintained
throughout.(Sal- Chart video 2)
5.3
Free-breathing analysis.
Video phase
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SynthTime-Subj Time
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SynthTime-Real phase
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Synth Time
Fig; showing the video phase of subject