Hemodynamics Flashcards
What is Poiseuille’s Law?
F = (change)P/R
How is blood flow affected by diff variables?
-blood flow is directly proportional to the pressure gradient
(better gradient, better flow)
-blood flow proportional to r^4
(lil increase in diameter increases blood flow dramatically)
-blood flow inversely proportional to resistance
(higher resistance, harder to flow)
-blood flow inversely prop to length and viscosity
(the longer the tube and the thicker the fluid, the slower the blood will flow)
How is resistance affected by diff variables?
proportional to length and viscosity
(cuz the longer the thicker, the higher the resistance)
inversely proportional to r^4
(the bigger the vessel, the lower the resistance)
What is the most important determinant of blood flow/
pressure gradient and r^4
pressure usually constant, so change in radius = major!
What is viscosity?
internal frictional resistance b/w adjacent layers of a fluid
What is a non-Newtonian fluid?
fluid whose viscosity changes over a range of shear rates and shear stress
aka blood! the diff layers [hetero: RBC, proteins etc] have diff velocities (higher in the middle)
so u get parabola!
How does hematocrit affect viscosity?
as hematocrit increases, have higher viscosity
normal: b/w 35-50%
What is anemia?
low hematocrit aka low viscocity
What is polycythemia?
high hematocrit aka high viscosity!
How is blood flow affected by viscosity?
as it slows down, viscosity goes up cuz higher chance of interaction b/w components
What is axial streaming?
RBC accumulate in the middle, line up
What is plasma skimming?
since RBC accumulate in middle, get more plasma to the sides
so this plasma is the one that goes into the smaller vessels
=hematocrit lower in smaller vessels
What is laminar flow?
fluid moves in parallel concentric layers within a tube
parabola!
fastest at middle and slower @ sides
What is turbulent flow?
disorderly pattern of fluid movement
When can you get turbulent flow?
murmurs, damage to endothelial lining (smoking), thrombi, korotkoff sounds
What is Reynold’s number?
indicates propensity for turbulent blood flow
What are the determinants of Rey’s #?
NR = DV/viscosity
the larger the vessel and velocity, the higher the chance
Velocity of blood flow varies inversely with cross sectional area.
What does that mean?
the smaller the vessel, the faster it goes
the larger the vessel or the larger the total cross sectional area, the slower the blood will flow (e.g. capillaries)
What is the Bernoulli principle?
in a constant flow system, the total energy remains constant
What happens to the flow when there is an abrupt decrease in cross sectional area?
potential energy (pressure) is converted to kinetic energy (flow) so! the velocity of blood increases
How do you explain blood flowing from lower to higher pressure after stenoic region??
blood flows from a higher to a lower total energy
-total energy continuously decreases
What is the Laplace relationship?
Tension = Pressure x Radius / wall thickness
How does Laplace explain why aneurisms rupture?
@ the aneurysm there is a buldge
-bigger radius!
-thinner wall! (cuz stretching)
-higher are so blood slows down => higher potential energy! (lateral P)
all those add up to a higher tension so distends a lil more
+ feedback
how do you explain that capillaries don’t rupture when jump too hard?
They have small radius so low tension: can withstand large pressures ^^
Why is it easier to vasoconstrict arteries?
Cuz larger wall thickness than lumen diameter
= low tension!
-super lil changes can make a diff
Why are dilated hearts dangerous?
they have a larger radius so larger wall tension so higher afterload to overcome
this requires more O2 consumption
Tell me about resistance in series
you add the individual resistances to get the total resistance
How are arteries and veins of the circulatory system arranged?
series!
aorta-large arteries-small arteries-arerioles-capillaries-venules-veins-vena cava
What is the primary site of arterial resistance?
arterioles
Tell me about resistance in parallel
the total resistance is less than the individual!
cuz add it 1/R
What is arranged in parallel?
organs and vessels!
Where does the larger drop of arterial pressure happen?
at largest resistance! which is at arterioles
Why do capillaries have the lowers resistance?
cuz have largest total resistance!
Why do veins hold 60% of the total blood volume??
cuz larger cross sectional area
plus high compliance
Compare and artery and a vein
- artery has an elastic lamina, veins dont
- arteries have more smooth muscle than veins
- arteries have less connective tissue than veins
What is the compliance properties of arterial wall components?
most compliant: elastic lamina
mid: smooth muscle
least: collagen (connective tissue)
What is a continuous capillary?
no fenestrations (holes) in wall
tight junctions between cells
continuous basal lamina
found in muscle & connective tissue
What is a fenestrated capillary?
holes with or without diaphragms (openings)
con’t basal lamina
found in kidney, intestine
What is a discontinuous (sinusoidal) capillary?
le swiss cheese: discont cells separated by wide spaces
discont basal lamina
found in liver, bone marrow, spleen
Which vessel has the most elastic tissue?
aorta- most compliant
distends + recoils the best <3
Which vessels are the easiest to control (lowest wall tension)? Least?
arteriole and precapillary sphincter
thick wall, small lumen
least: veins: thin walls with large diameters
Why is compliance important in aortic function?
blood passive by creates P
when have a high compliance:
the wall distends decreases pressure (used to move wall)
when the aortic valve closes the wall has some stored KE energy and recoils
The energy is put back into the pressure
=> holds the diastolic pressure high!
When low compliance: none of the P is converted into KE, all goes into PE => higher systolic
no recoil so dont add extra energy => lower diastolic
Why is an increase in pulse pressure bad?
cuz u changing the afterload!
Why does compliance decrease at higher volumes?
cuz stretched out the elastic! now trying to stretch the collagen =.= (aint gonna work)
-if keep stretching can lead to higher pressures
Why is the aorta a hydraulic filter?
the distended aortic wall recoils and acts as a secondary pump
What happens when the aorta is less compliant? Why would this happen?
if less compliant: wider pulse pressure and more work for the heart
why? cuz old V.V
Why are arteries called resistant vessels?
cuz have constant low compliance at all pressures
Why are veins called capacitance vessels?
cuz they have a high compliance due to geometry
can accommodate very large volumes of blood with little increase in pressure
*at higher pressure the compliance is low: allow saphenous veins to be used as coronary bypass grafts
What is a pressure pulse?
a wave that travels down the wall (depends on compliance)
