Biomedical Engineering Reference
In-Depth Information
3000
Heart Rate (1st Harmonic)
2500
Respiration
2000
2nd Harmonic
1500
3rd Harmonic
1000
500
0
0
10
20
30
40
50
60
70
80
m (DFT sample number)
FIGURE 11.34
DFT of pressure data from Figure 11.2. The first, second, and third harmonics of the heart rate
are clearly visible.
frequencies (similar to Fourier transform), and suppressing, denoising, and/or compressing
signals.
For comparison purposes, discrete Fourier transforms and discrete wavelet transforms
are illustrated for the pressure waveforms shown in Figure 11.2. Figure 11.34 shows details
of the DFT on the entire record of data. The beat-to-beat differences are reflected by the
widened and irregular values around the harmonics of the heart rate. The respiration influ-
ence is apparent at the very low frequencies.
Finally, an example from the MATLAB Wavelet Toolbox is shown that uses the same pres-
sure waveform. Figure 11.35 is a 2D rendering of the wavelet transform coefficients. The
x
-axis shows the scales, with the low scales on the bottom
and the high scales on the top. The top scale clearly shows the two respiratory cycles in the
signal. More informative than the transform coefficients, however, is a selective sample of
the signal details and approximations. As the scale is changed from a1 to a7, the approxima-
tion goes from emphasizing the heart rate components to representing the respiration compo-
nents. The details show that the noise at the heart rate levels is fairly random at the lower
scales but moves to being quite regular as the heart rate data become the noise (Figure 11.36).
-axis shows the positions and the
y
11.9 ARTIFICIAL INTELLIGENCE TECHNIQUES
Artificial intelligence (AI) is a broad field that focuses on the application of computer
systems that exhibit intelligent capabilities. AI systems can be built from a number
of separate technologies, including fuzzy logic, neural networks, and expert systems. The
principal aim of AI is to create intelligent machines that can function under adverse and
unpredictable circumstances. The term
intelligent
as it applies to machines indicates
