12
Other Biomedical Signals
12.1 INTRODUCTION AND OVERVIEW
Besides the main biomedical signals introduced in the previous chapter, there are
some other signals captured from other biomedical system that are used for medical
diagnostics. In this chapter, we briefly introduce some of these signals and discuss
their applications in medicine.
12.2 BLOOD PRESSURE AND BLOOD FLOW
In our description of an electrocardiogram (ECG), we reviewed the functions
of the cardiovascular system. Blood pressure is one of the vital signals used to
detect a wide range of abnormalities. In typical measurements of the blood pressure, many clinical processes are limited to measurement of only systolic and
diastolic pressures (as opposed to the entire signal). However, when the entire
blood pressure signal is collected, much more information can be extracted from
the data.
Typical measurements of blood pressure signal can be categorized as extravascular and intravascular measurements. The typical measurement of blood pressure,
which is often limited to measurement of systolic and diastolic pressure, is the popular sphygmomanometer and stethoscope system, which is considered as the gold
standard of extravascular blood pressure measurement systems. On the other hand,
the intravascular measurement of blood pressure signal is often conducted using
arterial catheter placement. The catheter placement is often used to measure the
entire blood pressure signal as opposed to recording only the high and low peaks in
the sphygmomanometer and stethoscope system.
A typical blood pressure signal over two pulses is shown in Figure 12.1. As can
be seen in the figure, this stochastic but periodic signal can be readily analyzed using
Fourier techniques. In practical applications, after decomposition using Fourier
transform or FT (or more precisely discrete Fourier transform or DFT), the amplitude of the FT (or the poser spectrum in stochastic analysis of the signal) in six
frequencies are calculated and analyzed. These six frequencies are the pulse rate, f 0 ;
its second harmonic, 2f 0 ; the third harmonic, 3f 0 ; the forth harmonic, 4f 0 ; the fifth
harmonic, 5f 0 ; and finally the sixth harmonic, 6f 0 . The reason for the popularity of
these frequencies is the fact that most of the energy of the blood pressure signal is
contained in these harmonics. Moreover, the relative strength or weakness of these
harmonics is often associated with certain abnormalities. The preceding discussion
explains why Fourier analysis is often used for processing and analysis of blood
pressure signal.
237
Other Biomedical Signals
12.1 INTRODUCTION AND OVERVIEW
Besides the main biomedical signals introduced in the previous chapter, there are
some other signals captured from other biomedical system that are used for medical
diagnostics. In this chapter, we briefly introduce some of these signals and discuss
their applications in medicine.
12.2 BLOOD PRESSURE AND BLOOD FLOW
In our description of an electrocardiogram (ECG), we reviewed the functions
of the cardiovascular system. Blood pressure is one of the vital signals used to
detect a wide range of abnormalities. In typical measurements of the blood pressure, many clinical processes are limited to measurement of only systolic and
diastolic pressures (as opposed to the entire signal). However, when the entire
blood pressure signal is collected, much more information can be extracted from
the data.
Typical measurements of blood pressure signal can be categorized as extravascular and intravascular measurements. The typical measurement of blood pressure,
which is often limited to measurement of systolic and diastolic pressure, is the popular sphygmomanometer and stethoscope system, which is considered as the gold
standard of extravascular blood pressure measurement systems. On the other hand,
the intravascular measurement of blood pressure signal is often conducted using
arterial catheter placement. The catheter placement is often used to measure the
entire blood pressure signal as opposed to recording only the high and low peaks in
the sphygmomanometer and stethoscope system.
A typical blood pressure signal over two pulses is shown in Figure 12.1. As can
be seen in the figure, this stochastic but periodic signal can be readily analyzed using
Fourier techniques. In practical applications, after decomposition using Fourier
transform or FT (or more precisely discrete Fourier transform or DFT), the amplitude of the FT (or the poser spectrum in stochastic analysis of the signal) in six
frequencies are calculated and analyzed. These six frequencies are the pulse rate, f 0 ;
its second harmonic, 2f 0 ; the third harmonic, 3f 0 ; the forth harmonic, 4f 0 ; the fifth
harmonic, 5f 0 ; and finally the sixth harmonic, 6f 0 . The reason for the popularity of
these frequencies is the fact that most of the energy of the blood pressure signal is
contained in these harmonics. Moreover, the relative strength or weakness of these
harmonics is often associated with certain abnormalities. The preceding discussion
explains why Fourier analysis is often used for processing and analysis of blood
pressure signal.
237