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S3: Cardio 9:00-10:00
Scribe: Sunita Jagani
Friday April 10, 2009
Proof: Sally Hamissou
Dr. Park
Hemodynamics of the Vasculature
Page 1 of 5
Dr. Parks had incomplete thoughts but I tried to follow along as best as I could. Any additional notes are in
italics.
I.
Introduction [S1]: Hemodynamics of the Vasculature
a. How things move [audio out until 0:49]
b. Difference between convection and compliance.
c. Convection is in terms of the stream, like sand being pulled with the stream, it is related to velocity of the flow,
basically pulling with it.
d. Capacitance-how well something stretches like a balloon. Balloon stretches so it’s compliant. The pressure
doesn’t go up, it just stretches and gets bigger.
e. If a hose put more pressure and going into the hose, and if it can’t stretch, then pressure goes higher.
f. If is rigid, then it has little compliance, then if you put more pressure, it can’t change, so it increases pressure.
II. Objectives [S2]
a. Distribution of blood volume, flow, pressure, vessel resistance throughout the circulatory system.
b. Discuss Poiseuille's Law and the effects of radius, length, viscosity and resistance on blood flow.
c. Limitations of applying classical hemodynamics to blood.
d. Hemodynamics can be used to express the changes we see.
III. Hemodynamics [S3]
a. Ohm’s law- old concept that has been around for a long time. Relate ohm’s law to cardiovascular physiology
b. The physical properties of blood, blood vessels and the heart and their interactions. It compares things like
pressure, flow, and resistance.
c. From Ohm’s law we get there is a flow pattern, driving force, and resistance to it. Same for voltage, current, and
resistance.
d. The mean arterial pressure is MAP. The flow is CO, and how resistance is total peripheral resistance caused by
the blood vessels in series.
e. It’s actually the pressure difference, one to another part of the vessel-delta pressure. We will be using this for
the rest of the lecture.
f. Consists of :
i. Pressure = Mean Arterial Pressure (MAP)
ii.
Flow = Cardiac Output (CO)
iii.
Resistance = Total peripheral resistance (TPR)
IV. Effect of Pressure Difference on Blood Flow [S4]
a. Looking at a cross segment of vessel, how pressure is 100 at one end, and 10 at the other end. What is the
flow? 10
b. What if you change something? Change to 500 and 410 mmHg. Nothing happens to flow. The delta pressure is
90 has not changed. The driving force is delta pressure.
c. Delta pressure is the flow.
i. Flow is proportional to pressure difference.
V. Flow is inversely proportional to vessel length [S5]
a. These are tubes made of glass, two outlet system.
b. Pressure difference determining the height of the fluid. Flow is 10 mL/s.
c. Length of A and make it twice as long as B, the flow goes down. This is proportional to vessel length.
d. The longer the vessel length, the slower the flow.
VI. Flow is dependent on 4th power of the radius [S6]
a. Same chamber, flow, diameter, and length, but change the vessel radius.
b. (Normal is from the previous slide of side A)
c. Change the radius and doubled it. The flow has gone from 160 m/s to 10 m/s, it’s to the 4th power of radius. Not
just proportional, it’s to the 4th power.
d. Radius has the most impact to the flow. If you double the flow, 2 to the 4th-> it’s 16x different. It’s the most
important concept.
VII. Effect of radius on flow [S7]
a. Change radius, the flow moves to the fourth power
VIII. Graph [S8]
a. Other things can affect it as well like viscosity which is how thick the blood is. Like oil is more vicious than water.
b. The blood has a plasma component, and a blood component that has cells and proteins to make more viscous.
c. Hematocrit- take the blood out and spin out; it’s the blood cell vs. total blood. Normal is 40%-45% blood cells
and the rest is water.
S3: Cardio 9:00-10:00
Scribe: Sunita Jagani
Friday April 10, 2009
Proof: Sally Hamissou
Dr. Park
Hemodynamics of the Vasculature
Page 2 of 5
d. Decrease the viscosity, the flow is proportional to it.
e. Can have disease that has a hematocrit of 60%-65%, high amount of red blood cells. Can’t understand then
name of the disease. Very viscous and high resistance. The treatment for the disease is bleeding. It affects the
vasculature and makes the heart work really hard.
f. Viscosity is inversely proportional to the blood flow.
IX. Flow is inversely proportional to viscosity [S9]
a. More viscous, the flow goes down proportionally. 50% is normal, here is the water, plasma, and you can see
blood.
X. Poiseuille’s Law [S10]
a. Most important relationship, and based on the ohm’s law little bit.
b. Q = ΔP π r4
c.
ήL 8
d. It has: Q= is the flow, change in pressure, radius (has pi R-squared), viscosity and length terms.
e. You have to know this equation. With this you know all about the vessel and how it’s going to respond. Here is
the flow coming in, should know what happens to the blood flow.
f. It there is the change of the radius there will be a dramatic increase or decrease, if you double it, changes it 16x,
if you half it, it decreases by 16x.
g. The length, viscosity will affect it all well. All these terms in one equation.
h. [S11] Assumptions for this P Law
i. Flow is steady (constant)
1. Not really true because the pump (heart) is pulsatile
2. Also that arterial vessels dampen changes but they actually do, but not steady
ii. Flow is laminar
1. Generally true except at bifurcations
iii. Fluid is Newtonian
1. Newtonian fluid is homogeneous, fixed viscosity
2. Is suspension, non-homogeneous
3. Viscosity increases with increasing hematocrit
i. Assumptions, not absolute but to get handle on how fluid relates to these concepts.
j. [S12] Know the equation
i. Take the equation, and solve for the various variables. We take the law to solve for resistance, or ohm’s
law.
ii. Know the main equation.
iii. Know how resistance changes the blood flow, and know the Poiseuille’s law.
iv. Q = ΔP π r4
v.
ήL 8
vi. Q = ΔP/R
vii. R = ΔP/Q
viii. R = 8 ή L
ix.
π r4
x. Where: R = Resistance ή = Viscosity of Blood L = length of blood vessel R4 = radius of blood vessel
raised to the 4th power
XI. Effect of the diameter of the blood vessel on the velocity of blood flow [S13]
a. Summary slide. Read off the slide. Change the area to 10 X, the velocity goes down.
b. Basically change in diameter affects the velocity of the flow.
XII. Cardiovascular Dynamics [S14]
a. Contrast enhanced MRI angiogram. We are looking at flow, it’s compared by colors, high velocity is red, blue is
slow velocity. Red is the bottom, something happened to the flow to changes the velocity. See at the
bifurcations which is branching to different systems (renal etc). Some pattern of change in flow.
XIII. Coarctation of the Aorta [S15]
a. See a lot of red-high velocity flow inside the normal blue color. Something causing turbulence because we have
coarctation stenosis of the aorta that is disrupting the normal flow pattern. Velocity is somehow changing.
Seems to be associated with change in the diameter of the vessels and bifurcation of the vessels.
XIV.
Laminar Flow [S16]
a. Normally, the vessel looks like this. It’s called laminar. As the blood goes across the vessel, there is a little bit of
resistance that slows it down. It goes further from the resistance it has a faster flow rate and the Vmax is in the
center because it has the least amount of resistance there.
S3: Cardio 9:00-10:00
Scribe: Sunita Jagani
Friday April 10, 2009
Proof: Sally Hamissou
Dr. Park
Hemodynamics of the Vasculature
Page 3 of 5
b. So the flow forms a bullet form pattern of cylinders. If you look at the cross-section of the velocity, its sticking to
the blood vessel on the outside, and in the middle it’s going the maximum flow rate. There is a concentric layer
of fluid, that’s the pattern and very energy efficient and easy for the heart and blood vessels.
c. Whenever possible, you want laminar flow.
XV. Figure: Velocity Profiles [S17]
a. Normal– laminar. You can get something coming back is that is turbulent flow. It goes backwards on itself, not
energy efficient. There are velocity changes that cause it to go from laminar flow to turbulent flow. Something
causes it to be not efficient anymore. There is a consequence of that, still need blood to come through, so you
run into a problem.
XVI.
Figure: Laminar vs. Turbulent Flow [S18]
a. Velocity-highest velocity is parabolic.
b. Turbulent- going against yourself. It takes more force to put the same amount of blood through.
XVII. Laminar and Turbulent Flow [S19]
a. Laminar Flow
i. all points in fluid move parallel to walls of tube
ii. Each layer of blood stays at same distance from wall
iii. Blood cells go to center of vessel, plasma goes to the outside
b. Turbulent Flow
i. At bifurcations of blood vessels
ii. Pressure drop greater than with laminar flow, with laminar flow coming back on top of itself.
iii. Makes heart work harder
iv. Blood clots and thrombi much more likely to develop at the branch points
XVIII. Effect of turbulence on pressure-flow relationship [20]
a. Here is the flow pattern and the turbulent flow. For pressure, this is efficient.
b. Need higher pressures to get the same flow out.
c. Turbulent Flow- decreases flow at any given pressure. Is less efficient.
XIX.
Pressure-Flow Relationship [S21]
a. You can relate this using Reynolds number. It’s a dimensionless number relates inertial forces (movement of
flow through) to viscous forces. And that’s what we’re talking about for laminar vs. turbulent flow.
b. You have a driving force, there is no noise
c. You hear noise in the turbulent flow because it keeps hitting the vessel back and forth. There is critical velocity
which is Reynold’s number about 2,000, just a certain point where we are not efficient anymore.
d. Plaque could cause changes in the normal smooth pattern of the vessel. Can hear this by doing an ultrasonic on
it and hear noise. Hear noise in the aorta and carotid and can measure it. Noisy pattern means not efficient.
e. Also have a problem in clotting. Don’t want clots!
XX. Figure v=(Q/A) [S22]- skipped
XXI.
Parallel and Series Circuits [S23]
a. Systemic circuit is made up of two different parts. There is branching up here and those are parallel circuits.
b. The most common pattern in our body is through the artery system through series of capillaries network and
then to venous system and back up to the heart. That’s in series.
c. Our anatomical system consists of a series of parallel and series circuits. Whether we are in a parallel or series
arrangement, resistance is different.
XXII. Series and Parallel resistance [S24]
a. You have Flow, pressure pushing things along, the two pressures determined by resistance. If you put a resistor
here, then get a change in voltage.
b. Resistances determined by the pressure at the end. It’s changed by the resistors.
c. The parallel circuit-branch off, we get two kinds of resistances and pressures. This is a different change in
resistance than in series.
XXIII. Figure Student Consult [S25] **initially skipped but came back at the end
a. This is related to systolic and diastolic pressure. There is the highest pressure is the systolic part contracting
and pushing all the cardiac output into the vessel. The cardiac output is how much is ejected by the heart in
course of a minute. Each stroke volume times your heart rate. Heart rate is about 70 beats per minute. Every
beat we eject this out. Cardiac output is about 5-6 L/min. The heart goes up to 120. The diastolic pressure
pushes all the blood vessel (muscular type), at the end of that heart beating the heart has gone down, it’s the 2 nd
force.
b. Mean arterial pressure is near the diastolic pressure than systolic pressure. Mean pressure is not half way
between. We will talk about the physiological reason later.
c. Pulse pressure is the difference between the diastolic and systolic. Sometimes gets larger or smaller. Can have
hypertension, and then higher systolic pressure and maybe the diastolic stays the same. Some ppl can have
S3: Cardio 9:00-10:00
Scribe: Sunita Jagani
Friday April 10, 2009
Proof: Sally Hamissou
Dr. Park
Hemodynamics of the Vasculature
Page 4 of 5
diastolic pressure being higher. These can different consequence. If you don’t have the second force pushing
the vessel back in, can have lots problem and less blood delivery during the diastolic phase.
d. Heart gets its blood supply during relaxation and the heart is perfused during diastole. If the heart rate
increases, less time for the delivery to the heart. If you keep going higher, then you get a point where the blood
can’t supply the heart anymore. Then you can get more consequences like pains because not enough blood
supply to the heart called angina. Can get metabolic changes as well.
e. When listening through a stethoscope through the arm, hear a sound because of flow. Listening for an absence
of sound. When you start deflating the cuff, the first thing you hear is sound related to blood coming through
which can be related to the hear pushing out blood in systole. Get systolic pressure, when getting diastolic
pressure, the sound goes away. Pump above systolic, listen for the presence of the sound, and then loss of the
sound is how you get the blood pressure.
XXIV. Figure [S26]
a. This showing the arrangement of the arteries, arterioles, veins, venules all in series. The resistance is the sum
of each individual resistances (1st +2nd ….). all these determine the end point.
b. Then you have the aorta, branching of in parallel. It’s 1/resistance. It’s the sum of inverse of the resistances.
c. There is a different pattern of resistances in series and parallel.
XXV. Law of LaPlace [S27]
a. Resistance is different in terms of parallel and series. We will talk later about this in terms of pathology.
b. Another concept is the law of LaPlace. This is concept is tricky.
c. This is looking at a tube, making a cut, and how it affects the wall tension.
i. Forces is that is going to push in open, another force that pushes back.
1. One of the forces inside is the pressure coming in and pushing outside which is called the
intravascular pressure.
2. The other force is outside trying to pushing it back in is called tissue pressure and they are related.
ii. Wall tension is what we are feeling right now, it is the tension the tear we have. We are looking at the
radius, and the length of vessel. These determine the tension in the vessel wall.
d. Vessels are built to handle the tension. But if there is an increase in the intravascular pressure, the wall tension
increases. If there more stuff placed in there, there is a stretching the vessel. The vessel will have increase in
the tension, the smooth muscle is going to go backwards and push it back together which is the opposing force.
e. The smooth muscles contracts back and wall tension goes back to normal.
f. Those two forces determine law of LaPlace. Possible test question
XXVI. Law of LaPlace [S28]
a. Tension is related to the change in pressure which is the transmural pressure. Transmural means across the
vessel- the difference between the outside and inside. It’s related to the radius and wall thickness.
b. T = (∆P*r) / µm
Where T = tension in the vessel wall
∆P = Transmural pressure
r = radius of the vessel
µm = wall thickness
XXVII. Law of LaPlace [S29]
a. Here is a balloon. The pressure is the same across the balloon because we put the same amount of air.
b. In middle part, the tension is related to the pressure and the radius. So the radius here is much larger. If there is
constant pressure and high radius, then there will be high tension. If 4x radius, then 4x up tension because we
have stretched it.
c. If it’s half that side further along the balloon, the wall tension is less because it’s not as stretched.
d. At the end where no radius, almost no wall tension.
e. Can see differences in how it’s stretched into wall tension. The more is stretches, more wall tension and that
causes aneurysm. It has some physiological problems in the resistance, delta pressure and resistance.
f. The wall tension should be maintained, and can oppose it by changing a smooth muscle tissue pressure.
XXVIII. LaPlace’s Law Explains [S30-31] went back and forth between the slides
a. At given a pressure, for a constant pressure, increasing the radius, leads to increase in tension.
b. That explains why the arteries have to have thicker wall because has higher pressure. It has thicker walls to
dissipate the wall tension. Higher blood pressure in arteries.
i. The other part of the equation is devised by the wall thickness
ii. If there is thicker wall, then tension is less. These arteries have wall thickness to keep the tension right.
c. Capillaries have low pressure so there is very thin wall. Less tension because of less pressure and thinner walls.
d. So looking at the arrangement that determines very thick arteries, very thin capillaries based on LaPlace Laws.
e. Also:
i. Aneurysms
S3: Cardio 9:00-10:00
Scribe: Sunita Jagani
Friday April 10, 2009
Proof: Sally Hamissou
Dr. Park
Hemodynamics of the Vasculature
Page 5 of 5
ii. Blood vessel distensibility
iii. Effects of ventricular dilatation on contraction-Wall thickness applies to the heart and thickness of the
ventricular walls and chamber walls
f. This is the take home.
g. For given BP, increasing the radius of the vessel leads to a increase in tension.
h. Arteries must have thicker walls than veins because they carry much higher BP.
i. Capillaries also carry significant BP, but unlike arteries, capillary walls are thin. Small size leads to reduced level
of tension so thick walls not needed.
j. Conclusions: Properties of this relationship helps us understand the variable thickness of arteries, veins, and
capillaries.
End [32:38]