12 Biomedical Engineering Fundamentals
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increases with increase in oxygen consumption at an instant. The heart period which
is a reciprocal of heartbeat is generally referred to as RR interval (the time interval
between two consecutive R peaks in ECG signal). The only criterion for considering
the RR interval is that the sampling frequency should be very high (>500 Hz) to
assess the sinoatrial node activities.
The heart rate variability (HRV) is another standard term which describes heart
period oscillation as well as the oscillation between consecutive instantaneous
values of heart rate. The HRV is very closely related to the mechanism of the
autonomic nervous system which gives immediate response to any physiological
states such as respiration phase, sleep stages, and emotional activities. The HRV is
also good in representing functional integrity of a physiological process (thermal,
hormonal, neural, etc.) Therefore, the assessment of HRV gives early signs of
pathological developments such as cardiovascular diseases [34].
12.5.1.2 Respiration
In the respiration process, the lung plays a major role which delivers oxygen to
the bloodstream and releases carbon dioxide from the blood through a rhythmic
expansion and contraction process. The assessment of respiratory cycle performs an
important role in the diagnosis of various diseases. There are numerous methods to
register the respiration on which the three well-established methods are discussed
here [34].
In the first method, the mechanorespirogram signal is a mechanical biomedical
signal used to record the circumference changes of the abdomen and chest during
breathing. A periodic waveform showing respiratory rate is observed through this
process during normal breathing. On the other hand, this waveform disappears
during holding of breath. The amplitude deflection in this signal increases during
snoring in order to overcome an increased respiratory resistance. The recorded
mechanorespirogram signal from the abdomen and chest may differ in amplitude
and phase due to different strengths of abdominal and chest breathing. The waveform recorded from abdominal breathing is delayed with respect to the waveform
recorded with chest during breathing [34].
The lung sounds are also present in PCG signal during normal breathing due
to air turbulences in the lung branching airways. These sounds have much lower
amplitude; due to this reason, it cannot be easily distinguished over time. In addition,
an overlapping signal component is also recognizable during the inspiration phase
of snoring sounds. This signal component is present due to elastic oscillations of the
pharyngeal walls which may lead to a temporal closure of the airways [34].
In the third method, a mechanical biomedical signal is used which records the
airflow through the mouth considering nasal airflow is stopped using a tube with a
woven screen inside which acts as a flow resistance. This method is commonly used
in clinical practice. In this method, the airflow is considered positive and negative
corresponding to inspiration and expiration during normal breathing, respectively.
The flow is zero during holding of breath. The high-frequency oscillations of the
581
increases with increase in oxygen consumption at an instant. The heart period which
is a reciprocal of heartbeat is generally referred to as RR interval (the time interval
between two consecutive R peaks in ECG signal). The only criterion for considering
the RR interval is that the sampling frequency should be very high (>500 Hz) to
assess the sinoatrial node activities.
The heart rate variability (HRV) is another standard term which describes heart
period oscillation as well as the oscillation between consecutive instantaneous
values of heart rate. The HRV is very closely related to the mechanism of the
autonomic nervous system which gives immediate response to any physiological
states such as respiration phase, sleep stages, and emotional activities. The HRV is
also good in representing functional integrity of a physiological process (thermal,
hormonal, neural, etc.) Therefore, the assessment of HRV gives early signs of
pathological developments such as cardiovascular diseases [34].
12.5.1.2 Respiration
In the respiration process, the lung plays a major role which delivers oxygen to
the bloodstream and releases carbon dioxide from the blood through a rhythmic
expansion and contraction process. The assessment of respiratory cycle performs an
important role in the diagnosis of various diseases. There are numerous methods to
register the respiration on which the three well-established methods are discussed
here [34].
In the first method, the mechanorespirogram signal is a mechanical biomedical
signal used to record the circumference changes of the abdomen and chest during
breathing. A periodic waveform showing respiratory rate is observed through this
process during normal breathing. On the other hand, this waveform disappears
during holding of breath. The amplitude deflection in this signal increases during
snoring in order to overcome an increased respiratory resistance. The recorded
mechanorespirogram signal from the abdomen and chest may differ in amplitude
and phase due to different strengths of abdominal and chest breathing. The waveform recorded from abdominal breathing is delayed with respect to the waveform
recorded with chest during breathing [34].
The lung sounds are also present in PCG signal during normal breathing due
to air turbulences in the lung branching airways. These sounds have much lower
amplitude; due to this reason, it cannot be easily distinguished over time. In addition,
an overlapping signal component is also recognizable during the inspiration phase
of snoring sounds. This signal component is present due to elastic oscillations of the
pharyngeal walls which may lead to a temporal closure of the airways [34].
In the third method, a mechanical biomedical signal is used which records the
airflow through the mouth considering nasal airflow is stopped using a tube with a
woven screen inside which acts as a flow resistance. This method is commonly used
in clinical practice. In this method, the airflow is considered positive and negative
corresponding to inspiration and expiration during normal breathing, respectively.
The flow is zero during holding of breath. The high-frequency oscillations of the