Download Cardio92-Hemodynamics

Cardio #92
Thurs, 01/30/03, 9am
Dr. Smith
Jennifer Uxer
Page 1 of 5
Hemodynamics
I.
Dr. Downey
 Dr. Downey spoke for about the 1st ten minutes to complete the highlights of
yesterday’s lecture. This material is now testable.
A. Valvular Dysfunction
1. This is not stressed in detail but know and understand the following
rudimentary points.
2. Stenosis—means the valve does not open normally
 If it doesn’t open normally, more pressure than usual is dissipated
through the stenotic valve.
 Aortic valvular stenosis—
 Initially, there is decreased blood pumped out of the ventricle and
more blood inside the ventricle at the end of systole. End diastolic
volumes increase. Ventricle responds with a more forceful
contraction. Muscle mass of the chamber increases (hypertrophy)
due to the constant distending force.
 Left ventricular peak pressure is significantly elevated
(150mmHg or higher) to get a nearly normal stroke volume
through a smaller than normal opening. Systemic arterial
pressure is about normal due to the body’s control mechanisms.
This creates a significant pressure gradient across the
stenotic valve.
 Stenotic valves cause higher resistance to blood flow. So, greater
pressure is needed to force the same amount of blood (as compared
to normal) through them.
3. Incompetent—blood leaks back across the valve
 If the aortic valve is incompetent, each stroke volume must be greater
than normal to pump away the blood that regurgitated retrogradely.
 The left ventricle must work harder to pump away the blood from the
pulmonary circulation AND the regurgitated blood.
4. Know that the left ventricle must work harder for each condition.
5. Increase in preload is a compensation for larger than normal end systolic
volumes. Moving up the Starling curve, you use more optimal sarcomere
length to deal with the increase in pressure. The increase in afterload is
compensated by the increase in preload.
6. Cardiac Output
 Know this principle (remember equation) for measuring cardiac
output. Applies or an individual organ or to the entire system.
Cardio #92
Thurs, 01/30/03, 9am
Dr. Smith
Jennifer Uxer
Page 2 of 5

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II.
III.
Resting person uses about 250ml O2/minute
Arterial: 20ml of O2/100ml of blood
Venous: 15ml of O2/100ml of blood (You get a sample of mixed
venous blood from the pulmonary artery using a catheter.)
 Be able to work problems using these to determine the cardiac
output.
7. Splitting of the Second Heart Sound—Dr. Downey didn’t read the power
point, but commented that he’d seen board questions on this. The 2nd heart
sound is often 2 sounds. The splitting can be increased by inspiration,
which sends more blood into the right heart. It takes a little longer for
pulmonic valve to close because there’s temporarily a larger stroke volume
from the right ventricle.
Dr. Smith lecture
 In depth information on valves and their disorders will be covered for our 6th
exam in 2 weeks.
 We’ll review pressure/volume loops and Wigger’s Diagram changes with
valvular disorders.
 The review questions were skipped in the interest of time.
Basic Principles
A. Arteries vs Veins
1. Form and function are directly linked due to the wall thickness, lumen/wall
ratio, and amount of elasin present
2. Pressures and Compliance (capacitance)
 Arterial tree is a high pressure system for blood delivery (primary
function)
 Venous system is a compliant system.
3. Most of our blood is in the veins.
B. Ohm’s Law
1. Pressure is a function of flow and resistance (in the arteries and in the
systemic circulation)
2. ΔP = Q * R
C. Flow through a vessel
1. Laminar vs. Turbulent—normal blood flow is laminar when there is not
branching.
a. Laminar Flow
 Smooth, quiet flow that occurs in a conical shape. This shape is
made up of layers parallel to the vessel walls.
Cardio #92
Thurs, 01/30/03, 9am
Dr. Smith
Jennifer Uxer
Page 3 of 5

There’s relative drag on the particles from 1 layer to the next.
Greatest drag is on the outer layer. At the edge of the blood vessel
lumen, there’s virtually no velocity in the blood flow.
 As you move toward the center of the vessel, each layer moves with
a faster velocity due to decreased drag.
 Maximum velocity of blood flow is at the center of the blood vessel.
 Flow is more efficient.
b. Turbulent Flow
 Reynold’s number has reached a threshold.
 Wavelets are created, and the conical profile of movement is
destroyed. Eddies are created—what occurs at a bifurcation.
 Vibrations and noise are produced. This is what we can hear.
 Flow velocity is decreased.
2. Bifurcations—most common place for turbulence where there is not
pathology
3. Reynold’s number
 Can be calculated, but we won’t be asked to do this.
 A high Reynold’s number, above a certain threshold, is indicative of
turbulent flow. A number of factors can contribute to this.
 Is a function of the velocity, density and viscosity of the substance
flowing (blood), and the diameter of the tube.
 Use this concept to measure blood pressure. Shift the flow from laminar
to turbulent where it can be heard.
D. Poiseuille’s Law
1. Derived during the mid 1800s by a French physicist using a rigid glass tube;
however our blood vessels are distensible. So, it doesn’t work perfectly.
2.
Q = ΔP r4
ηL
3. Flow is a function of
 The pressure gradient—a direct/linear relationship. This is also related
to Ohm’s Law. Relate the 2 equations.
 The radius of the vessel to the 4th power.
 Take Home message: Primary control mechanisms for blood flow to
tissue are vasoconstriction and vasodilation. Small changes in the vessel
cause large changes in flow due to the radius change. System regulates
the radius of vessels, not the pressure gradient.
4. η is viscosity. Isn’t changed on a moment to moment basis, so it’s usually
not a factor (although it can affect the flow). Main determinant of viscosity
is hematocrit.
5. L is the length of the tube. This can affect the flow, but the body doesn’t
change this to regulate systems. So, it’s irrelevant in this case.
6. By the equation, there’s a linear relationship between flow and pressure
change. In reality, this isn’t true. If you increase the pressure, the tube will
Cardio #92
Thurs, 01/30/03, 9am
Dr. Smith
Jennifer Uxer
Page 4 of 5
distend, enlarging the radius. This increases the flow even more for that
given pressure.
7. Where is resistance in here? Functionally, it has to do with the radius.
Flow is inversely related to resistance. Radius is inversely related to
resistance. Ohm’s law—think with it when considering systemic circulation
(blood pressure). Poiseuille’s law—think with it when you’re considering
blood flow to a tissue—local control.
 If you exercise, you engage muscles. Nothing really changes in the
kidney and GI. Only muscle metabolism increases, so vessels increase
radius to dilate.—Poiseuille’s Law. (Actually the vessels in the kidney
and GI constrict to compensate to maintain blood pressures since the
muscle vessels are dilated.)
8. Graph showing the effect of change in viscosity:
 Top line doesn’t occur because you don’t have a hematocrit of 0.
 Polycythemia—large number of RBCs, so blood is thick and viscosity is
increased. For a given pressure, flow is decreased. This is the principle
of blood doping—take some blood out and give it back later to increase
the # of RBCs. Helps in endurance activities because of the increased
O2 carry capacity. Can carry it too far and impair flow.
E. Blood Flow Velocity
1. v = Q/A
2. Won’t use this in terms of physiology in the clinic. It’s used in
measurement making.
3. Velocity is
 Directly related to flow
 Inversely related to the cross sectional area of the blood vessel.
4. It is used in Doppler measurements with ultrasound. These are used to
measure velocity through the blood vessels in a non-invasive way. The
measurement of flow velocity will allow you to calculate flow.
5. Cross sectional area is greatest in the capillaries, so flow velocity is lowest
in the capillaries.
6. Ultrasound measurements of flow velocity were shown. The normal shape
looked like this:


Velocity increased as a pulse of blood moves through the vessel and
decreases as the blood passes.
In carotid artery stenosis, velocity decreases, there are no crisp
peaks (key element) as shown above, and you’ll hear sounds due to
turbulence.
Cardio #92
Thurs, 01/30/03, 9am
Dr. Smith
Jennifer Uxer
Page 5 of 5
F. Systemic Vascular Resistance
1. Rearrange Ohm’s Law to solve for this.
2. Resistance is directly related to pressure gradient and inversely related to
cardiac output.
3. SVR = ΔP/Q
4. Change in systemic resistance can represent a change in afterload to the
heart. Increase in resistance decreases flow.
G. Resistance in Series
1. Resistance can be oriented in series—1 right after the other—heart to aorta
to arteries to smaller arteries to arterioles to capillary bed.
2. At any given point is a resistance that’s a function of pressure gradient and
flow.
3. Total resistance is the sum of the resistances at each level of the circuit as
you passed through it. Calculate the resistances for the arterial side, venous
side.
4. SVR=ΔP / Q
 For systemic vascular resistance:
 Through the entire systemic circulation, what’s the pressure
gradient?
Thinking mean arterial pressure: 100mmHg out of the
heart and 0mmHg back into the heart. So, ΔP is mean arterial
pressure = 100mmHg.
 Cardiac output is 5.
 SVR=ΔP / Q = 100 / 5 = 20 mmHg/L/min
 If you have heart failure and blood backs up, you have to take this
into account for the pressure calculation.
5. Aorta through the major arteries through the capillaries—How is flow
changing? It’s the same through all of them. Pressure changes at each
level.
6. As you move through the circuit, you have resistances. The largest
resistance is in the arterioles—the largest pressure gradient. Next greatest is
through the capillaries. Venous system is generally low resistance.
7. Use the chart of easy values provided to make total resistance calculations to
ensure understanding.