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R. B. Pachori and V. Gupta
flattened in a reproducible way. The flattening removes the tangential forces in the
arterial wall and the rounded probe is barely exposed to the artery pressure. During
flattened artery, the applied force by the rounded probe is opposite and equal to the
pulsatile force. This force exerts in such way that the pressure of blood exerts on the
flattened arterial wall. This rounded probe is connected to a pressure sensor which
reflects waveform of blood pressure. This method requires an initial calibration
with the patient to compensate changes of arterial mechano-elastic function among
patients in order to obtain absolute blood pressure values [34].
Blood Flow
The recording way of blood flow is analogous to blood pressure. The blood flow can
also be recorded in invasive and noninvasive ways. The stroke volume, blood flow
velocity, and pulsatile flow waveform are the parameters of interest in blood flow
registration [34].
The invasive methods for blood flow monitoring have fewer acceptances due to
invasiveness and related complications. Some of the invasive methods are indicator
method, electromagnetic method, and transit-time ultrasonic method [34].
In indicator method, the oxygen is used as an indicator which is introduced into
the stream of blood flow and the resulting arterial as well as venous concentrations
from this indicator are measured based on Fick principle. Alternatively, a thermistor
catheter is used to introduce a bolus of ice-cold saline into the right atrium. This
catheter is also used to detect the resulting drop in temperature of the blood which
is present in the pulmonary artery. The amount of indicator injected divided by the
area under the blood temperature dilution curve represents the cardiac output in this
method. In the second method, the blood vessel with flowing blood is exposed to
electromagnetism. The blood vessel is placed in transverse magnetic field which
induced a potential difference in the blood vessel with flowing blood. This potential
difference is directly proportional to internal diameter of the vessel and the mean
blood flow velocity which can be used to measure the blood flow. In the last transittime ultrasonic method, an ultrasound beam (wave) passes through the blood vessel.
There are two ultrasound receivers placed diagonally on either side of the vessel.
The difference of time taken for the ultrasound to pass in one direction as opposed
to the other is used to obtain waveform for the flow velocity of blood [34].
The noninvasive methods for the determination of blood flow parameters are
frequently acceptable. There are many methods for the noninvasive registration of
blood flow from which three of the most popular are echocardiographic method,
impedance cardiography method, and pressure pulse contour method [34].
The echocardiographic method is based on ultrasonic Doppler effect. In this
method, an ultrasound beam in the frequency range of a few MHz is backscattered
from the moving blood cells. The blood velocity is related to frequency shift due
to backscattered sound. In other words, the frequency increases when the blood
moves toward the ultrasound probe. The volumetric blood flow can be computed
from the velocity profile over the cross-sectional area of the vessel combined with
R. B. Pachori and V. Gupta
flattened in a reproducible way. The flattening removes the tangential forces in the
arterial wall and the rounded probe is barely exposed to the artery pressure. During
flattened artery, the applied force by the rounded probe is opposite and equal to the
pulsatile force. This force exerts in such way that the pressure of blood exerts on the
flattened arterial wall. This rounded probe is connected to a pressure sensor which
reflects waveform of blood pressure. This method requires an initial calibration
with the patient to compensate changes of arterial mechano-elastic function among
patients in order to obtain absolute blood pressure values [34].
Blood Flow
The recording way of blood flow is analogous to blood pressure. The blood flow can
also be recorded in invasive and noninvasive ways. The stroke volume, blood flow
velocity, and pulsatile flow waveform are the parameters of interest in blood flow
registration [34].
The invasive methods for blood flow monitoring have fewer acceptances due to
invasiveness and related complications. Some of the invasive methods are indicator
method, electromagnetic method, and transit-time ultrasonic method [34].
In indicator method, the oxygen is used as an indicator which is introduced into
the stream of blood flow and the resulting arterial as well as venous concentrations
from this indicator are measured based on Fick principle. Alternatively, a thermistor
catheter is used to introduce a bolus of ice-cold saline into the right atrium. This
catheter is also used to detect the resulting drop in temperature of the blood which
is present in the pulmonary artery. The amount of indicator injected divided by the
area under the blood temperature dilution curve represents the cardiac output in this
method. In the second method, the blood vessel with flowing blood is exposed to
electromagnetism. The blood vessel is placed in transverse magnetic field which
induced a potential difference in the blood vessel with flowing blood. This potential
difference is directly proportional to internal diameter of the vessel and the mean
blood flow velocity which can be used to measure the blood flow. In the last transittime ultrasonic method, an ultrasound beam (wave) passes through the blood vessel.
There are two ultrasound receivers placed diagonally on either side of the vessel.
The difference of time taken for the ultrasound to pass in one direction as opposed
to the other is used to obtain waveform for the flow velocity of blood [34].
The noninvasive methods for the determination of blood flow parameters are
frequently acceptable. There are many methods for the noninvasive registration of
blood flow from which three of the most popular are echocardiographic method,
impedance cardiography method, and pressure pulse contour method [34].
The echocardiographic method is based on ultrasonic Doppler effect. In this
method, an ultrasound beam in the frequency range of a few MHz is backscattered
from the moving blood cells. The blood velocity is related to frequency shift due
to backscattered sound. In other words, the frequency increases when the blood
moves toward the ultrasound probe. The volumetric blood flow can be computed
from the velocity profile over the cross-sectional area of the vessel combined with