Download Cardio-Pulmonary Module 19 October 2009 HEMODYNAMICS Jude

Cardio-Pulmonary Module
19 October 2009
Jude Eric L. Cinco, MD
HEMODYNAMICS
Objectives:
 To discuss the basic physiology of the
cardiovascular system
o Specifically, hemodynamics
I.
The Cardiovascular System:
Primary function:
 To deliver blood to the tissues, providing essential
nutrients to the cells for metabolism and removing
waste products from the cells.
Others:
 Regulation of arterial blood pressure
 Delivery of regulatory hormones from the
endocrine glands to their sites of action if target
tissues
 Regulation of body temperature
 Homeostatic adjustments to altered physiologic
states
II.
1.
2.
3.
4.
5.
The Cardiac Cycle
Atrial systole: when the atrium contracts
Isovolumetric ventricular contraction
Ventricular ejection
Isovolumetric ventricular relaxation
Ventricular filling
***check Slide 14 of lecture powerpoint for diagram***
III.
Cardiovascular Physiology
systemic circulation: left heart and the systemic arteries,
capillaries, and veins
−The left ventricle pumps blood to all organs of the
body except the lungs.
pulmonary circulation: right heart and the pulmonary
arteries, capillaries, and veins
−The right ventricle pumps blood to the lungs.
cardiac output: the rate at which blood is pumped from
either ventricle
*left Cardiac Output is always equal to right Cardiac
Output.
* If you decrease heart rate, CO will fall.
***check Slide 15 of lecture powerpoint for diagram***
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
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IV.
Circuitry
1. Oxygenated blood fills the left ventricle.
 Blood that has been oxygenated in the lungs
returns to the left atrium via the pulmonary vein.
 This blood then flows from the left atrium to the
left ventricle through the mitral valve (the AV
valve of the left heart).
* Where do you expect to find the lowest possible oxygen
saturation in the circulatory system? Just before it enters the
lungs – in the pulmonary artery.
2. Blood is ejected from the left ventricle into the
aorta.
 Blood leaves the left ventricle through the aortic
valve (the semilunar valve of the left side of the
heart), which is located between the left ventricle
and the aorta.
 When the left ventricle contracts, the pressure in
the ventricle increases, causing the aortic valve to
open and blood to be ejected forcefully into the
aorta.
 Blood then flows through the arterial system,
driven by the pressure created by contraction of
the left ventricle.
3. Cardiac output is distributed among various organs.
 via sets of parallel arteries:
o 15% of the cardiac output is delivered to
the brain
o 5% is delivered to the heart
o 25% is delivered to the kidneys and so
forth
 total systemic blood flow equals the cardiac
output.
 percentage distribution of cardiac output is not
fixed.
 three major mechanisms change blood flow to an
organ system:
a. CO remains constant, blood flow is
redistributed via selective alteration of
arteriolar resistance.
b. CO increases or decreases, but
percentage distribution of blood flow is
kept constant.
c. a combination of the first two
mechanisms
* not all organ systems receive same amount of CO; there is a
priority. All organ systems are NOT perfused equally. CO is a
constant. Arteriolar resistance alters CO, not the heart.
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
4. Blood flow from the organs is collected in the veins.
 blood leaving the organs is venous blood and
contains waste products from metabolism, such as
carbon dioxide (CO2).
 mixed venous blood is collected in veins of
increasing size and finally in the largest vein, the
vena cava.
 the vena cava carries blood to the right heart.
5. Venous return to the right atrium.
 the right atrium fills with blood (venous return.)
 In the steady state, venous return to the right
atrium equals cardiac output from the left
ventricle.
6. Mixed venous blood fills the right ventricle.
 Mixed venous blood flows from the right atrium to
the right ventricle through the AV valve in the
right heart, the tricuspid valve.
* Mixed venous blood that has returned from all tissues and
mixed in the right atrium. Mixed venous blood is taken from the
pulmonary artery.
7. Blood is ejected from the right ventricle into the
pulmonary artery.
 The RV contracts and blood is ejected through the
pulmonic valve (the semilunar valve of the right
side of the heart) into the pulmonary artery, which
carries blood to the lungs.
 In the capillary beds of the lungs, oxygen (O2) is
added to the blood from alveolar gas, and CO 2 is
removed from the blood and added to the alveolar
gas.
 Thus, the blood leaving the lungs has more O 2 and
less CO2 than the blood that entered the lungs.
 Note that the cardiac output ejected from the
right ventricle is identical to the cardiac output
that was ejected from the left ventricle.
8. Blood flow from the lungs is returned to the heart
via the pulmonary vein.
 Oxygenated blood is returned to the left atrium via
the pulmonary vein to begin a new cycle.
V.

Hemodynamics
refers to the principles that govern blood flow in
the cardiovascular system.
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
basic principles of physics similar to those applied
to the movement of fluids in general.
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***See Slides 38-39 for charts***
A. Velocity of Blood Flow

rate of displacement of blood per unit time.
* Relative to all the arteries and capillaries, the aorta is
smallest.
*. Aorta – has smallest surface area and largest velocity.
*In terms of cross sectional area, there are more in the
smaller vessels. Capillaries contain the largest cross
sectional area (surface area).
Sample Problem:
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V = Q/A
V = Velocity of blood flow (cm/sec)
Q = Flow (mL/sec)
A = Cross-sectional area (cm2)
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Group 2
Velocity of blood flow (v) is linear velocity and is
expressed in units of distance per unit time (e.g.,
cm/sec).
Flow (Q) is volume flow per unit time and is
expressed in units of volume per unit time (e.g.,
mL/sec).
Area (A) is the cross-sectional area of a blood
vessel (e.g., aorta) or a group of blood vessels
(e.g., all of the capillaries).
Area is calculated as A = πr2, where r is the radius
of a single blood vessel (e.g., aorta) or the total
radius of a group of blood vessels (e.g., all of the
capillaries).
Araño, Escobillo, Peña, Ronquillo, Yu
The smallest vessel represents the aorta, the
medium-sized vessel represents all of the arteries,
and the largest vessel represents all of the
capillaries.

A man has a cardiac output of 5.5 L/min.
The diameter of his aorta is estimated to be 20
mm, and the total surface area of his systemic
capillaries is estimated to be 2500 cm2.
What is the velocity of blood flow in the aorta
relative to the velocity of blood flow in the
capillaries?
Solution:
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
Hence, velocity in the aorta is 800-fold that in the
capillaries (1752 cm/min in the aorta compared
with 2.2 cm/min in the capillaries).
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* Blood loss due to stabbing in the aorta would be due to high
velocity.
The resistance of the entire systemic vasculature
(a.k.a. systemic vascular resistance).
TPR can be measured with the flow, pressure, and
resistance relationship by substituting cardiac
output for flow (Q) and the difference in pressure
between the aorta and the vena cava for ΔP.
R = ΔP/Q
Sample Problem:
B. Relationships between blood flow, pressure
and Resistance
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Blood flow through a blood vessel or a series of
blood vessels is determined by two factors: the
pressure difference between the two ends of the
vessel (the inlet and the outlet) and the resistance
of the vessel to blood flow.
The pressure difference is the driving force for
blood flow, and the resistance is an impediment to
flow.
The relationship is analogous to the relationship of
current (I), voltage (ΔV), and resistance (R) in
electrical circuits, as expressed by Ohm's law
Ohm's law ΔV = I × R or I = ΔV/R
The equation for blood flow is expressed as
follows:
Renal blood flow is measured by placing a flow meter on a
woman's left renal artery. Simultaneously, pressure probes
are inserted in her left renal artery and left renal vein to
measure pressure. Renal blood flow measured by the flow
meter is 500 mL/min. The pressure probes measure renal
arterial pressure as 100 mm Hg, and renal venous pressure
as 10 mm Hg. What is the vascular resistance of the left
kidney in this woman?
Solution:
R = P/Q
= (Pressure in renal artery – Pressure in renal vein)/ renal
blood flow
= (100 mmHg – 10 mmHg) / 500 mL / min
= 90 mmHg / 500 mL / min
= 0.18 mm Hg/mL/min
Q = ΔP/R
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Q = Flow (mL/min)
ΔP = Pressure difference (mm Hg)
R = Resistance (mm Hg/mL/min)
The direction of blood flow is always from high to
low pressure.
Increasing resistance (e.g., by vasoconstriction)
decreases flow, and decreasing resistance (e.g., by
vasodilation) increases flow.
The major mechanism for changing blood flow in
the cardiovascular system is by changing the
resistance of blood vessels, particularly the
arterioles.
In order to maintain a constant flow of blood, given the
area changes, the velocity has to adapt
Blood flow is directly proportional to pressure, and
inversely proportional to resistance. Total peripheral
resistance dictated by ohms law.
Unit is mm / Hg / mL / minute.
C.
Group 2
Total Peripheral Resistance
Araño, Escobillo, Peña, Ronquillo, Yu
D. Resistance to Blood Flow
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from blood vessels and blood itself
The relationship between resistance, blood vessel
diameter (or radius), and blood viscosity is
described by Poiseuille's equation.

Stroke is caused by decreased flow due to increased
resistance

(not 'pooh-zuls', it is pronounced 'pwah-zweez'')
1.
Poiseuille Equation:
R = Resistance
η = Viscosity of blood ('eta')
l = Length of blood vessel
r4 = Radius of blood vessel raised to the fourth power

resistance to flow is inversely proportional to the
fourth power of the radius (r4) of the blood vessel.
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for example, if the radius of a blood vessel
decreases by one half, resistance does not simply
increase twofold, it increases by 16-fold (24)!
Sample Problem:
A man suffers a stroke caused by partial occlusion of his left
internal carotid artery. An evaluation of the carotid artery
using magnetic resonance imaging (MRI) shows a 75%
reduction in its radius. Assuming that blood flow through
the left internal carotid artery is 400 mL/min prior to the
occlusion, what is blood flow through the artery after the
occlusion?
Solution:
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The internal carotid artery is occluded, and its
radius is decreased by 75%. Another way of
expressing this reduction is to say that the radius is
decreased to one-fourth its original size.
The first question is How much would resistance
increase with 75% occlusion of the artery? The
answer is found in the Poiseuille equation. After
the occlusion, the radius of the artery is onefourth its original radius; thus, resistance has
increased by 1/(1/4)4, or 256-fold.
The second question is What would the flow be if
resistance were to increase by 256-fold? The
answer is found in the flow, pressure, resistance
relationship (Q = ΔP/R).
Since resistance increased by 256-fold, then flow
decreased to 1/256, or 0.0039, or 0.39% of the
original value. The flow is 0.39% of 400 mL/min, or
1.56 mL/min.
2. Series and Parallel Resistance

The total resistance of the system arranged in
series is equal to the sum of the individual
resistances
Rtotal = Rartery + Rarterioles + Rcapillaries + Rvenules + Rveins

The total resistance in a parallel arrangement is
less than any of the individual resistances
a.
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Series Resistance
illustrated by the arrangement of blood vessels
within a given organ.
each organ has a major artery and a major vein.
within the organ, blood flows from the major
artery to smaller arteries, to arterioles, to
capillaries, to venules, to veins.
arteriolar resistance is the greatest and thus
greatly determines the total resistance
The arrangement of blood vessels within a given organ
is in series
b. Parallel Resistance
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
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illustrated by the distribution of blood flow among
the various major arteries branching off the aorta
there is parallel simultaneous blood flow through
each of the circulations (e.g., renal, cerebral, and
coronary).
the flow through each organ is a fraction of the
total blood flow.
with this arrangement there is no loss of pressure
in the major arteries and that mean pressure in
each major artery will be approximately the same
as mean pressure in the aorta.
adding a resistance to the circuit causes total
resistance to decrease, not to increase.
for example: Four resistances, each = 10, are
arranged in parallel.
total resistance is 2.5 (1/Rtotal = 1/10 + 1/10 + 1/10
+ 1/10 = 2.5).
if a fifth resistance with a value of 10 is added to
the parallel arrangement, the total resistance
decreases to 2 (1/Rtotal = 1/10 + 1/10 + 1/10 + 1/10
+ 1/10 = 2).

Thus if you graft a vessel directly to the aorta, total
resistance will decrease.

on the other hand, if the resistance of one of the
individual vessels in a parallel arrangement
increases, then total resistance increases.
for example: four blood vessels, each resistance =
10 and with total resistance = 2.5.
if one of the four blood vessels is completely
occluded, its individual resistance becomes
infinite.
the total resistance of the parallel arrangement
then increases to 3.333 (1/Rtotal = 1/10 + 1/10 +
1/10 + 1/∞).
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Turbulent Flow
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E.
Laminar and Turbulent Flow
Laminar Flow
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The length of the arrows shows the approximate
velocity of blood flow.
Laminar blood flow has a parabolic profile, with
velocity lowest at the vessel wall and highest in
the center of the stream.
Turbulent blood flow exhibits axial and radial flow.
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Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
Ideally, blood flow in the CV system is laminar, or
streamlined.
In laminar flow, there is a parabolic profile of
velocity within a blood vessel, with the velocity of
blood flow highest in the center of the vessel and
lowest toward the vessel walls.
The parabolic profile develops because the layer of
blood next to the vessel wall adheres to the wall
and, essentially, does not move.
The next layer of blood (toward the center) slips
past the motionless layer and moves a bit faster.
Each successive layer of blood toward the center
moves faster yet, with less adherence to adjacent
layers.
The length of the arrows shows the approximate
velocity of blood flow.
Laminar blood flow has a parabolic profile, with
velocity lowest at the vessel wall and highest in
the center of the stream.
Turbulent blood flow exhibits axial and radial flow.
When an irregularity occurs in a blood vessel (e.g.,
at the valves or at the site of a blood clot), the
laminar stream is disrupted, and blood flow may
become turbulent.
In turbulent flow, the fluid streams do not remain
in the parabolic profile but, instead, the streams
mix radially and axially.
Because energy is wasted in propelling blood
radially and axially, more energy (pressure) is
required to drive turbulent blood flow than
laminar blood flow.
Turbulent flow is often accompanied by audible
vibrations called murmurs.
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Reynold’s Number (NR)

a dimensionless number that is used to predict
whether blood flow will be laminar or turbulent.
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NR = Reynold's number
Has no unit
ρ = Density of blood ('rho')
d = Diameter of blood vessel
v = Velocity of blood flow
η = Viscosity of blood ('eta')
If (NR) is less than 2000, blood flow will be
laminar.
If it is greater than 2000, there is increasing
likelihood that blood flow will be turbulent.
Values greater than 3000 always predict turbulent
flow.
The major influences on Reynold's number in the
cardiovascular system are changes in blood
viscosity and changes in the velocity of blood
flow.
Decreases in viscosity (e.g., decreased hematocrit)
cause an increase in Reynold's number.
Narrowing of a blood vessel, which produces an
increase in velocity of blood flow, causes an
increase in Reynold's number.
The effect of narrowing a blood vessel (i.e.,
decreased diameter and radius) on Reynold's
number is initially puzzling because, according to
the equation, decreases in vessel diameter should
decrease Reynold's number (diameter is in the
numerator).
however, the velocity of blood flow also depends
on diameter (radius), according to the earlier
equation, v = Q/A or v = Q/πr2.
Thus, velocity (also in the numerator of the
equation for Reynold's number) increases as
radius decreases, raised to the second power.
Hence, the dependence of Reynold's number on
velocity is more powerful than the dependence on
diameter.
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To illustrate the application of Reynold's number
in predicting turbulence:
Anemia is associated with a decreased hematocrit
(decreased mass of red blood cells) and, because
of turbulent blood flow, causes functional
murmurs. Reynold's number, the predictor of
turbulence, is increased in anemia due to
decreased blood viscosity.
A second cause of increased Reynold's number in
patients with anemia is a high cardiac output,
which causes an increase in the velocity of blood
flow (v = Q/A).
To illustrate the application of Reynold's number
in predicting turbulence.
Thrombi are blood clots in the lumen of a vessel.
Thrombi narrow the diameter of the blood vessel,
which causes an increase in blood velocity at the
site of the thrombus, thereby increasing Reynold's
number and producing turbulence.
F.
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Compliance of Blood Vessels
The compliance or capacitance of a blood vessel
describes the volume of blood the vessel can hold
at a given pressure.
Compliance is related to distensibility and is given
by
the
following
equation:
C=V/P
C = Compliance (mL/mm Hg)
V = Volume (mL)
P = Pressure (mm Hg)

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the higher the compliance of a vessel, the more
volume it can hold at a given pressure.
veins are most compliant and contain the
unstressed volume (large volume under low
pressure).

Veins are the capacitance vessels of the body. Veins
have higher compliance than the arteries.

arteries are much less compliant and contain the
stressed volume (low volume under high
pressure).
Laminar Flow and Reynold’s Number:
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
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flows from the arteries, to the arterioles, to the
capillaries, to the veins, and back to the heart.
This decrease in pressure occurs as blood flows
through the vasculature because energy is
consumed in overcoming the frictional resistances.
Mean pressure in the aorta is very high, averaging
100 mm Hg. Arterial walls have low compliance due
to thicker walls.
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The slope of each curve is the compliance.
Compliance of the veins is high; in other words,
the veins hold large volumes of blood at low
pressure. Compliance of the arteries is much lower
than that of the veins; the arteries hold much less
blood than the veins, and they do so at high
pressure.
The characteristics of the arterial walls change
with increasing age: The walls become stiffer, less
distensible, and less compliant.
At a given arterial pressure, the arteries can hold
less blood. Another way to think of the decrease in
compliance associated with aging is that in order
for an "old artery" to hold the same volume as a
"young artery," the pressure in the "old artery"
must be higher than the pressure in the "young
artery."
Arterial pressures are increased in the elderly due
to decreased arterial compliance.
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This high mean arterial pressure is a result of two
factors: the large volume of blood pumped from
the left ventricle into the aorta (cardiac output)
and the low compliance of the arterial wall.
The pressure remains high in the large arteries,
which branch off the aorta, because of the high
elastic recoil of the arterial walls.
Thus, little energy is lost as blood flows from the
aorta through the arterial tree.
Beginning in the small arteries, arterial pressure
decreases, with the most significant decrease
occurring in the arterioles.
At the end of the arterioles, mean pressure is
approximately 30 mm Hg.
This dramatic decrease in pressure occurs because
the arterioles constitute a high resistance to flow.
Arterioles have high resistance
Since total blood flow is constant at all levels of
the cardiovascular system, as resistance increases,
downstream pressure must necessarily decrease
(Q = ΔP/R, or ΔP = Q × R).
In the capillaries, pressure decreases further for
two reasons: frictional resistance to flow and
filtration of fluid out of the capillaries.
When blood reaches the venules and veins,
pressure has decreased even further.
Pressure in the vena cava is only 4 mm Hg and in
the right atrium is even lower at 0 to 2 mm Hg.
G. Pressures in the Cardiovascular System


Blood pressures are not equal throughout the
cardiovascular system.
If they were equal, blood would not flow, since
flow requires a driving force (i.e., a pressure
difference).
***See Slides 78 and 79***
Pressure Profile in the Vasculature

Group 2
The mean pressure is highest in the aorta and
large arteries and decreases progressively as blood
Araño, Escobillo, Peña, Ronquillo, Yu
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
Systemic arterial pressure during the cardiac
cycle. Systolic pressure is the highest pressure
measured during systole. Diastolic pressure is the
lowest pressure measured during diastole. Pulse
pressure is the difference between systolic
pressure and diastolic pressure.
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H. Arterial Pressure in the Systemic Circulation
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although mean pressure in the arteries is high and
constant, there are oscillations or pulsations of
arterial pressure.
These pulsations reflect the pulsatile activity of the
heart: ejecting blood during systole, resting during
diastole, ejecting blood, resting, and so forth.
Each cycle of pulsation in the arteries coincides
with one cardiac cycle.
Diastolic pressure is the lowest arterial pressure
measured during a cardiac cycle and is the
pressure in the artery during ventricular relaxation
when no blood is being ejected from the left
ventricle.
Systolic pressure is the highest arterial pressure
measured during a cardiac cycle. It is the pressure
in the artery after blood has been ejected from the
left ventricle during systole.
The "blip" in the arterial pressure curve, called the
dicrotic notch (or incisura), is produced when the
aortic valve closes. Aortic valve closure produces a
brief period of retrograde flow from the aorta
back toward the valve, briefly decreasing the
aortic pressure below the systolic value.
Pulse pressure is the difference between systolic
pressure and diastolic pressure.
If all other factors are equal, the magnitude of the
pulse pressure reflects the volume of blood
ejected from the left ventricle on a single beat, or
the stroke volume.
Pulse pressure can be used as an indicator of
stroke volume because of the relationships
between pressure, volume, and compliance.
Assuming that arterial compliance is constant,
arterial pressure depends on the volume of blood
the artery contains at any moment in time.
Mean arterial pressure is the average pressure in
a complete cardiac cycle and is calculated as
follows:
Mean Arterial Pressure = diastolic pressure + 1/3 pulse
pressure
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
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MAP = Diastolic pressure + 1/3 (Systolic pressure –
Diastolic pressure)
MAP = 3/3 Diastolic pressure + 1/3 Systolic
pressure – 1/3 Diastolic pressure
MAP = 2/3 Diastolic pressure + 1/3 Systolic
pressure
Notice that mean arterial pressure is not the
simple mathematical average of diastolic and
systolic pressures. This is because a greater
fraction of each cardiac cycle is spent in diastole
than in systole. Thus, the calculation of mean
arterial pressure gives more weight to diastolic
pressure than systolic pressure.
The pulsations in large arteries are even greater
than the pulsations in the aorta.
In other words, systolic pressure and pulse
pressure are higher in the large arteries than in the
aorta.
It is not immediately obvious why pulse pressure
should increase in the "downstream" arteries.
The explanation resides in the fact that, following
ejection of blood from the left ventricle, the
pressure wave travels at a higher velocity than the
blood itself travels (due to the inertia of the
blood), augmenting the downstream pressure.
Furthermore, at branch points of arteries, pressure
waves are reflected backward, which also tends to
augment pressure at those sites.
Given that blood flows from the aorta to the large
arteries, it may seem odd that systolic pressure
and pulse pressure are higher in the downstream
arteries.
The answer is that the driving force for blood flow
in the arteries is the mean arterial pressure, which
is influenced more by diastolic pressure than by
systolic pressure.
Note in that while systolic pressure is higher in the
large arteries than in the aorta, diastolic pressure
is lower; thus, mean arterial pressure is lower
downstream.
Although systolic pressure and pulse pressure are
augmented in the large arteries (compared with
the aorta), from that point on, there is damping of
the oscillations.
The pulse pressure is still evident, but decreased,
in the smaller arteries; it is virtually absent in the
arterioles; and it is completely absent in the
capillaries, venules, and veins.
This damping and loss of pulse pressure occurs for
two reasons:
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o
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(1) The resistance of the blood vessels,
particularly the arterioles, makes it
difficult to transmit the pulse pressure.
o (2) The compliance of the blood vessels,
particularly of the veins, damps the pulse
pressure-the more compliant the blood
vessel, the more volume that can be
added to it without causing an increase in
pressure.
Several pathologic conditions alter the arterial
pressure curve in a predictable way
pulse pressure will change if stroke volume
changes, or if the compliance of the arteries
changes.
pressure, pulse pressure, and mean pressure all
will be decreased.
Aortic regurgitation
 When the aortic valve is incompetent (e.g., due to
a congenital abnormality), the normal one-way
flow of blood from the left ventricle into the aorta
is disrupted.
 Instead, blood that was ejected into the aorta
flows backward into the ventricle.
 Such retrograde flow can occur because the
ventricle is relaxed (is at low pressure) and
because the incompetent aortic valve cannot
prevent it, as it normally does.
I.
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
Venous Pressure in the Systemic Circulation
By the time blood reaches the venules and veins,
pressure is less than 10 mm Hg; pressure will
decrease even further in the vena cava and the
right atrium.
The reason for the continuing decrease in pressure
is now familiar: The resistance provided by the
blood vessels at each level of the systemic
vasculature causes a fall in pressure.
Pressure and Velocity in the Systemic Circulation
Effect of arteriosclerosis and aortic stenosis on arterial
pressures.

Arteriosclerosis
 In arteriosclerosis, plaque deposits in the arterial
walls decrease the diameter of the arteries and
make them stiffer and less compliant.
 In order to preserve flow, you need higher pressure.
 Because arterial compliance is decreased, ejection
of a stroke volume from the left ventricle causes a
much greater change in arterial pressure than it
does in normal arteries (C = ΔV/ΔP or ΔP = ΔV/C).
 Thus, in arteriosclerosis, systolic pressure, pulse
pressure, and mean pressure all will be increased


TA: total cross-sectional area of the vessels, which
increases from 4.5 cm2 in the aorta to 4500 cm2 in
the capillaries
RR: relative resistance which is highest in the
arterioles
Arteriosclerosis is different from atherosclerosis,
athero is for the whole body, arterio is in the arteries.
Aortic stenosis
 If the aortic valve is stenosed (narrowed), the size
of the opening through which blood can be
ejected from the left ventricle into the aorta is
reduced. Thus, stroke volume is decreased, and
less blood enters the aorta on each beat. Systolic
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
Page 10 of 11
BATCH 2014  HEMODYNAMICS
K. The Law of Laplace
Wall tension (T) is equal to the product of the transmural
pressure (P) and the radius (r) divided by the thickness of
the wall (w):
T=Pr/w
J.






Venous Pressures
Circulation
in
the
Pulmonary
The entire pulmonary vasculature is at much lower
pressure than the systemic vasculature.
The pattern of pressures within the pulmonary
circulation is similar, however.
Blood is ejected from the right ventricle into the
pulmonary artery, where pressure is highest.
Thereafter, the pressure decreases as blood flows
through the pulmonary arteries, arterioles,
capillaries, venules, and veins and back to the left
atrium.
An important implication of these lower pressures
on the pulmonary side is that pulmonary vascular
resistance is much lower than systemic vascular
resistance.
This conclusion can be reached by recalling that
the total flow through the systemic and pulmonary
circulations must be equal (i.e., cardiac output of
the left and right hearts is equal).

Though the left ventricle is thicker than the right
ventricle (due to higher pressure exerted), both
produce the same Cardiac Output.

Because pressures on the pulmonary side are
much lower than pressures on the systemic side,
to achieve the same flow, pulmonary resistance
must be lower than systemic resistance (Q =
ΔP/R).
Group 2
Araño, Escobillo, Peña, Ronquillo, Yu
In chronic hypertension
(1) heart walls will thicken
(2) radius decreases
(3) chest pain is present, which is caused by lack of oxygen in the
heart. (as the heart muscle hypertrophies, coronary arteries
don’t hypertrophize)
(4) Eventually, the heart will become thinner and dilated due to
low oxygen received.
(5) When the heart fails, given low wall thickness, high pressure,
high radius, there is high tension.
“When in doubt, arterioles is the key.“
-Jude Eric L. Cinco, MD, 2009
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