1. ARTERIAL PRESSURE
• The mean arterial pressure (MAP) is defined as the
average arterial pressure during a single cardiac cycle .
• As blood is pumped out of left ventricle in to the
arteries pressure is generated . The MAP is determined
by Cardiac Output (CO).Systemic Vesicular Resistance
(SVR) and Central Venous Pressure (CVP).
• MAP= (CO*SVR ) + CVP
• (As CVP is near 0 mm Hg relationship can be simplified
as below)
• MAP = (CO*SVR)
2. • In practise the mean arterial pressure (MAP) is derived
from a patients Systolic Blood Pressure (DBP )
• Normal(MAP)is between 65 mm and 110 mm of Hg
• MAP=DP+1/3 Pulse Pressure ( PP=SP-DP)
CLINICAL SIGNIFICANCE
• MAP is better indicator of tissue perfusion than SBP
• Hence MAP is calculated for the management of
patients with acute conditions when there is a concern
for appropriate organ perfusion.
3. Pulse wave velocity (PWV) is a measure of arterial stiffness.
The properties of the arterial wall, thickness and the arterial
lumen diameter are the major factors influencing (PWV).
Velocity of pulse wave is independent and much higher than
the velocity of blood flow max velocity of blood flow is only 50
cm/s.
The rate of travel of the pulse wave is about
• 4 meters sec in aorta and its branches.
• 8 meters /sec in the large arteries .
• 16 meters /sec in the small arteries .
Aortic pulse wave velocity is a measure of aortic stiffness. It is
measured with ultrasound
Aortic pulse wave velocity is the predictor of cardiovascular
mortality in the hypertensive subjects
Velocity of circulation of pulse waves
4. Cardiac cycle causes flow & pressure waves
Relationship of pressure to flow is not simple
resistance but mechanical impedance which is time
dependent resistance is time dependent
Mechanical impedance consists of
• Viscous impedance that opposes flow.
• Compliant impedance that opposes volume.
• Inertial impedance that opposes change of flow.
Because of these resisive compliant and inertial
properties the pressure and flow waves are different .
5. Cardiac cycle causes flow & pressure waves
With increasing distance from the heart in the
large arteries the pressure curves become
steeper and the peak narrower and an
important secondary pressure oscillation
appears during diastole .
As the pressure wave travels down the large
arteries it gets distorted but not damped .
MAP falls slightly with increasing distance
from the heart.
6. Distortion of pressure waves
The pressure wave in the aorta is more
complex than a simple sine wave.
The complex waveform can be thought of the
algebric sum of many individual sine cosine
waves each with its own amplitude frequency
and phase.
The precise mathematical method by which
complex waveforms are broken down into
simpler components is called Fourier analysis.
7. Cardiac cycle causes flow & pressure waves
In terminal arteries and arterioles damping of
pressure waves predominates over distortion
because
Increase in number of parallel vessels
increases aggregate compliance damping the
pressure waves.
Having a small radius increases resistance
In capillaries damping is so severe that pulsations
do not occur and blood flow is continuous
8. Pulse wave harmonics
One of the most useful tools of arterial dynamics is the
Fourier analysis of the complex pulse waves in to their
simple sinusoidal harmonic components.
These harmonics are the simple functions described by
relatively simple mathematics so that calculations on
them are feasible .
Principle of superposition is applied in the arteries .
Summation of these harmonics leads in to a new
complex waves.
Digital computer is used to carry out the Fourier
analysis .
9. Evaluation of pulse wave morphology
by Fourier’s harmonic analysis
Evaluation of pulse waves on five segments of
lower limb in a recumbent healthy subject by
means of Fourier's analysis show following
phenomenon
:: constant and marked accentuation of the
amplitude of the second harmonic.
:: distinct diminution of the amplitudes of
further higher harmonics.
:: relative augmentation of amplitude in a distal
direction as a manifestation of mounting
impedance towards periphery.
10. Distortion of pressure waves
• Vessels become more stiffer towards the
periphery increasing wave velocity especially for
higher frequency components.
• Pressure waves bounce off the end of the arterial
tree and reflect back up the vessels.
• When we summate these various effect on the
sine wave and cosine wave components
downstream the reconstructed pressure wave
has a different (distorted) shape than the original
wave.
11. Circulation time
The time required for the blood to flow between two
given points .
It measures the average linear velocity of blood.
The time taken for the blood to pass through a given
circuit of the vascular system, for Ex; the pulmonary or
systemic circulation, from one arm to another, from
one arm to tongue, or from arm to lung; it is measured
by the injection into an arm vein of a substance, such
as sodium dehydrochlorate,ether,fluorescein,
histamine, or a radium salt which can be detected
when it arrives at another point in the vascular system.
12. Factors influencing circulation time
• Increased cardiac output.
• Exercise.
• Excitement.
• Adrenaline.
• Rise of BMR-all these factors increase the velocity
of blood and decrease C.T.
• C.T is important in diagnosis of right and left
sided failure, in differentiating bronchial and
cardiac asthma , myxoedema etc.
