Lecture 14 - Circulation/Hemodynamics Flashcards
What is Poiseulle’s Law Equation?
- steady laminar flow of fluids through uniform cylindrical tubes
- Cardiovascular system is composed of branching, elastic tubes of varying diameter non-newtonian fluid
Flow = change in pressure/ Resistance (R)
What is the equation for flow? What does it vary directly & inversely with?
Flow = [(P1-P2 * )Pi * r^4]/ 8L*n
Directly with:
- pressure gradient
- radius to the 4th
Inversely:
- Length of vessel
- viscosity
flow = CARDIAC OUTPUT
Why do small changes in radius cause large changes in blood flow?
blood flow is related to the fourth power of the radius
- therefore, small changes in radius cause LARGE changes in blood flow (increase)
If you double the diameter, how does flow change?
Increases 16 times
If you vasoconstrict a vessel by 2, how does blood flow change?
DECREASES by 16
How does resistance relate to length, viscosity, and radius? Directly & Inversely with what?
R= 8Ln(viscosity) / Pi * r^4
Directly:
- length
- viscosity
Inversely:
- radius to the 4th
What are the most important determinants of blood flow in the cardiovascular system? Which of these is usually constant?
- Pressure Gradient
- Radius
PRESSURE is held constant, so changes in radius cause LARGE changes in blood flow to a tissue/organ
As length of a vessel increases, how does resistance change? Viscosity?
Resistance INCREASES
- as viscosity increases, resistance INCREASES
If the Left & Right Ventricle generate the same cardiac output, why is the pressure generated by the LEFT Ventricle higher?
DUE TO RESISTANCE
- increased after load in the L. Ventrile causes by arterial blood pressure
- as pressure increases, resistance increases
P= Flow * Resistance
What is VISCOSITY?
Internal frictional resistance between adjacent layers of a fluid (lack of slipperiness)
What does viscosity depend on?
Shear Stress (pressure) / Shear rate (velocity)
Define:
1. Shear Stress
- Shear Rate
- Resistance to movement between Laminae (pressure)
2. Relative VELOCITY between laminae
How is shear rate distributed in blood vessels? How does low viscosity affect this?
PARABOLIC PROFILE
- faster velocities in the middle - more axial
- outermost = slowest & therefore highest pressure
- LOWER viscosity = SHARPER parabolic profile
What are units of viscosity?
Poise
dyne sec/cm^2
What is the difference between a newtonian & non-newtonian fluid? How do they relate to viscosity?
- Newtonian = viscosity is CONSTANT & HOMOGENOUS
- over range of shear stress/ shear rate
(plasma, water) - Non- newtonian:
- velocity not constant
- NOT homogenous
(whole blood)
How does hematocrit affect viscosity?
- As hematocrit increases, viscosity increases
What are 2 examples of low and high hematocrit & their relation w/ viscosity?
- Anemia = low hematocrit = low viscosity (causes murmurs due to turbulent flow)
- Polycythemia = HIGH hematocrit
- high viscosity
What is the normal range of hematocrit?
35% - 50%
Is the relationship between viscosity & hematocrit LINEAR?
No
- at a certain hematocrit percentage (more than 50%), viscosity DRASTICALLY increases
Why is viscosity created in blood vessels?
each layer flowing against the other
- viscosity created because layers have INTERNAL FRICTIONAL RESISTANCE against each other
If shear rate increases, and no significant change in pressure, how does this change viscosity?
this causes a DECREASE in viscosity!
What is blood doping?
- injecting previously refrigerated blood to INCREASE oxygen carrying capacity
- this also increases viscosity (which is only an issue for older people)
What is axial streaming? Does this cause more or less frictional resistance?
Tendency of RBCs to accumulate in AXIAL laminae (in the middle)
- line up one by one = LESS FRICTIONAL RESISTANCE
What is plasma skimming?
Tendency of smaller vessels to contain relatively MORE plasma and less RBC’s due to axial streaming
(line up in middle in smaller vessels & much less RBC’s)
What is the hematocrit in smaller vessels as compared to larger vessels? What is the term for this?
HIGHER in LARGER vessels
- lower in smaller due to PLASMA SKIMMING
As tube diameter increases, what else increases?1
- Viscosity
2. Hematocrit Ratio
If you decrease shear rate, how is viscosity affected?
INCREASES
If there is a decrease in velocity, and a decrease in DIAMETER, what is the net affect?
DECREASE IN VISCOSITY
- due to AXIAL STREAMING
What is the term for the following:
less RBC’s go off into smaller vessels because of axial streaming
PLASMA SKIMMING
- as tube diameter decreases, hematocrit DECREASES because there is more PLASMA here instead
What two reasons account for why is there a 45% hematocrit in Great Veins & 40% hematocrit in capillaries?
- Axial Streaming
- Plasma Skimming
- hematocrit in smaller vessel is less than the hematocrit of a larger vessel
What is laminar flow? Turbulent flow?
- Fluid moves in parallel concentric layers (parabolic profile)
- Disorderly pattern of fluid movement
What can turbulent flow cause (4)
- Murmurs
- damage to Endothelial Lining
- Thrombi
- Kortkoff sounds
The longer the tube, the more or less internal frictional resistance?
MORE internal frictional resistance
- pressure will INCREASE
What are Kortkoff sounds?
when we inflate the cuff & create the stenosis
- it created TURBULENT flow through the stenosis
created a CLICK due to the turbulent flow (artifically induced KOROTKOFF SOUNDS) - caused by increase in VELOCITY due to decrease in diameter
What is the term for stenosis of carotid artery causing a sound when you place the stethoscope over the carotid? Why does this occur?
BRUIT!
- stenosis causes TURBULENT flow
How do blood clots occur from turbulent flow?
damage to endothelial lining
- lead to blood clots
- break off
- rupture & cause embolisms
What is platelet aggregation?
THROMBI
What does Reynold’s number determine?
TURBULENT FLOW
- higher than 3000 = greater chance of turbulent flow
What is the equation for Reynold’s Number? What does it depend on?
RN = pDv / n (viscosity)
directly:
- density
- diameter
- velocity
Indirect:
- viscosity
What occurs at a critical velocity?
blood flow changes from LAMINAR to TURBULENT
higher velocity, density, and diameter = greater what?
REYNOLD’s number!
Why does a person with anemia develop murmurs?
- lower viscosity = higher chance of turbulent flow
- develop murmur at a stenosis
Where are you most likely to find a high reynolds number in the body, if viscosity was kept constant?
AORTA
- largest diameter
What causes turbulence in Kortkoff sounds?
VELOCITY
- by lowering diameter you increase the velocity
How does velocity change in an increase in cross-sectional area?
DECREASES!
- vary inversely
ex: putting thumb over a hose –> increases velocity by decreasing area
How are individual vessels affected vs. Capillaries by a change in area?
- Individual Vessels :
clot in carotid
- blood will squirt & you will hear a bruit - Capillary: blood will not squirt through the blocked capillary because it will find another place to go!
In a constant flow system, what happens to total energy?
stays CONSTANT
PE + KE = total energy
In a decrease in cross-sectional area (stenosis), PE is converted to what? How does pressure change & velocity?
- kinetic energy!
- Pressure DECREASED
because - VELOCITY INCREASED
The following are applications of what principle:
- Aortic Stenosis
- Atrial Stenosis
- Aneurysms
- Lateral Vs End Pressure
TOTAL ENERGY STAYES CONSTANT
- so in aneurysm as area increases (radius), velocity decreases, and pressure INCREASES
- as KE decreases, PE increases (change relative to one another to keep total energy CONSTANT)
Explain why blood from L. Ventricle can flow into the Aorta even though this is going AGAINST the pressure gradient (low to high)
Left. ventricle has decreases area upon contraction, resulting in INCREASED velocity (decreased pressure)
- the increase in velocity shows that blood flows from HIGH to LOW kinetic energy areas
Is total energy greater or less in a stenotic region as compared to regular vessel as it flows DOWN?
GREATER
- since velocity increased, energy is higher which allows it to flow down an ENERGY gradient (high to low)
What is the equation for wall tension?
Wall tension = Pressure * Radius/Wall Thickness
Define the wall tension for the following:
- Capillaries
- Arteriolar vasoconstriction
- Aneurysm
- Dilated Hearts
- Low WT due to SMALL RADIUS
- can withstand large pressure - low WT due to large WALL thickness/diameter ratio
- HIGH WT due to INCREASED RADIUS
= cannot withstand high transmural pressures = RUPTURE - HIGH WT - LARGE RADIUS - higher after load & more systolic work & higher oxygen consumption to overcome high wall tension
What do dilated hearts increase?
- systolic work
- (work to overcome after load)
- OXYGEN consumption
Wall tension is the force that does what?
RIPS something apart
- force pulling the heart or vessel apart (ex aneurysm or dilated heart)
The large diameter of a dilated heart causes an increase in what that impedes shortening?
AFTERLOAD
- Wall tension opposes shortening & generates enormous amount of systolic work & O2 consumption
In an aneurysm, how are the following changed:
- Flow
- Pressure
- Wall thickness
- decreased flow - due to increased radius
- Increased pressure (KE converted to PE - velocity has decreased)
- Wall thickness decreases - stretching a balloon (it is the denominator)
What is the major difference in resistance for systems in series and in parallel?
Series: total resistance is always higher than any resistance in a system
Parallel: total resistance is always LESS than any resistance in system (1/R total)
What is the primary site of arterial resistance? (largest resistance site?)
ARTERIOLES
What ar some vessels in series? Parallel?
Series: aorta, large arteries, small arteries, arterioles, capillaries, veins, venues, vena cava
Parallel: capillaries
Where is the largest CHANGE (drop) in arterial pressure?
ARTERIOLES!
- largest resistance (lowest pressure)
DO capillaries have low or high total resistance? Is the drop in pressure across the capillaries significant?
LOW total resistance since has LARGEST cross-sectional area (even though they have the smallest diameter)
- low drop in pressure because of this
What are two reasons that veins hold 60% of total blood volume (majority of our blood is in venous system)?
- HIGH COMPLIANCE
2. Larger cross-sectional area than arteries ***
Describe the following for Capillaries:
- Velocity
- Area
- Pressure
- SLOWEST velocity (largest area - varies inversely)
- LARGEST area
- smallest pressure drop/change
P=F/A
What are two reasons that Arteries hold only 18% of total blood volume?
- Small total area
2. LOW COMPLIANCE
What occurs during exercise to decrease overall peripheral resistance?
OPEN additional capillaries in parallel
– therefore total resistance DECREASES
What occurs during hemorrhage to INCREASE Total Peripheral Resistance?
- blood flow to many organ systems in parallel is SHUT DOWN
- so under sympathetic stimulation, blood is shunted to brain,heart, lungs
= INCREASE total resistance
- raising blood pressure
Why do the capillaries have a small amount of blood in them, even though they have the largest cross-sectional area? Why do they have the slowest velocity?
- SHORTEST LENGTH
2. Slow - so they can effectively exchange O2/CO2
Administering whole blood/saline during hemorrhage does what to the venous curve?
shifts venous curve UP
- increases CVP
- increases preload
- increases cardiac output
- INCREASE BP!
What is the reason that the viscosity of capillaries does not rise, since it has the slowest velocity (shear rate)?
Because of the small diameter - RBC’s line up in a line, more AXIAL streaming & PLASMA SKIMMING
so net viscosity is DECREASED
Where is the largest pressure drop? Why is this not the capillaries?
ARTERIOLES
- largest internal resistance since viscosity is increasing (lamina flowing against each other increasing the internal friction)
= DECREASE IN PRESSURE because of increase in frictional resistance
Flow = P/R
- because there is a large amount of capillaries, the pressure is distributed amongst them
Where is there NO pulse pressure?
CAPILLARIES
