Flashcards in Lecture 14 - Circulation/Hemodynamics Deck (72)
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
- radius to the 4th
- Length of vessel
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
- radius to the 4th
What are the most important determinants of blood flow in the cardiovascular system? Which of these is usually constant?
1. Pressure Gradient
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?
- 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)
1. Shear Stress
2. Shear Rate
1. 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?
- faster velocities in the middle - more axial
-outermost = slowest & therefore highest pressure
- LOWER viscosity = SHARPER parabolic profile
What are units of viscosity?
What is the difference between a newtonian & non-newtonian fluid? How do they relate to viscosity?
1. Newtonian = viscosity is CONSTANT & HOMOGENOUS
- over range of shear stress/ shear rate
2. Non- newtonian:
- velocity not constant
- NOT homogenous
How does hematocrit affect viscosity?
- As hematocrit increases, viscosity increases
What are 2 examples of low and high hematocrit & their relation w/ viscosity?
1. Anemia = low hematocrit = low viscosity (causes murmurs due to turbulent flow)
2.Polycythemia = HIGH hematocrit
- high viscosity
What is the normal range of hematocrit?
35% - 50%
Is the relationship between viscosity & hematocrit LINEAR?
- 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
2. Hematocrit Ratio
If you decrease shear rate, how is viscosity affected?
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
- as tube diameter decreases, hematocrit DECREASES because there is more PLASMA here instead