Hemodynamics Flashcards
systole
blood into atria
contraction
diastole
blood into ventricles
arteries - flow, pump, compressibility
pulsatile flow
heart is pump
non-compressible
veins- flow, pump, compressibility
less pulsatile, phasic
leg contractions is pump
compressible
where are there valves
heart and veins
regurgitation
when the valves dont close enough
venous hemodynamic factors (2)
hydrostatic pressure
respiration
hydrostatic pressure - how does it change?
pressure supine vs standing
increases with increasing distance below heart
supine- 0 mmHg
standing- 100 mmHg
Describe how thoracic and abdominal volume (and pressure) changes with inspiration. What happens to venous return?
inspiration
increased thoracic volume, decreased pressure
decreased abdo volume, increased pressure
STOPS venous return
Describe how thoracic and abdominal volume (and pressure) changes with expiration. What happens to venous return?
expiration
decreased thoracic volume, increased pressure
increased abdo volume, decreased pressure
venous blood RETURNS from legs
what is valsalva and what does it do?
breath hold
increases abdo pressure, STOPS venous return
fluid
liquid or gas
driving force behind fluid flow
pressure, low to high
pressure formula
P = force/area
volumetric flow rate - what is it and whats the unit
volume of blood passing a point per unit time
applies to LONG STRAIGHT TUBE
mL/s
volumetric flow rate (Q) basic formula
Q = pressure/resistance (in vessel)
Resistance of a long straight tube depends on
tube length
viscosity
radius
poise
viscosity and resistance
If tube LENGTH increases what happens to flow RESISTANCE
length and resistance proportionate related
if tube RADIUS increases what happens to flow RESISTANCE
radius and resistance inversely related (to the power of 4!)
if VISCOSITY increases what happens to flow RESISTANCE
viscosity and resistance proportionately related
poise is what units
1 gram per cm^4-s
how much more viscious is plasma than water
50%
viscosity normal blood is what times that of water
5 times
what happens to flow rate if you increase resistance
Q and R are inversely related so decreases
How does resistance depend on radius? If radius doubles, what happens to resistance?
Resistance depends on radius to the 4th power
radius doubles, resistance decreases X16 (2^4)
how does vasodilation and vasoconstriction change flow resistance
vasodilation- decreases resistance
vasoconstriction- increases resistance
When do you use the poiseuille equation?
when resistance is not known
what happens to flow rate if you decrease diameter (according to poiseuille’s law)
flow rate decreases
what happens to flow rate if you increase length
flow rate decreases (because resistance increases)
volumetric flow rate in a tube depends on
pressure difference
length of tube
diameter of tube
viscoscity of fluid
what are the two types of flow
laminar and turbulent
what is laminar flow
flow in which layers of fluid slide over eachother in straight lines
types of laminar flow (3)
plug flow
parabolic flow
disturbed flow
Flow is seen at a stenosis or bifurcation
Disturbed flow
Plug flow
Flow seen at the entrance to tubes where the same speed is seen across the vessel
The fastest speed seen in parabolic flow? the slowest? what is the average flow speed?
fastest= centre
slowest= tube walls
average flow speed is 1/2 the fastest speed
Type of flow seen after significant stenosis
Turbulent flow
Flow where you’ll hear bruit
Turbulent
Characterizing factor for turbulent flow
critical reynolds number, 2000 for blood
Factors affecting reynolds number
density (p) velocity diameter ------------- viscosity
stenosis vs occulsion
partial vs complete blockage
what is pulsatile flow
non-steady, acceleration and deceleration over cardiac cycle
true or false - venous circulation is such that pressures, flow speed and patterns do not change over time
true
with pulsatile flow, blood flow speed/pressure changes. this depends on (3)
impedence
intertia
compliance
what are two things observed in compliant vessels with pulsatile flow
windkessel effect
flow reversal
what is the windkessel effect
observed in compliant vessels where
systole = vessel expands and volume increases
distole = pressure decreases, compliant vessel contracts producing extended flow without driving pressure from the heart
true or false - blood stops flowing during diastole
false
what causes flow reversal and where is it seen
reversal of flow because decreased pressure and vessel contraction without valves to prevent back flow.
Not seen in the aorta because of valves
what is the continuity rule
the volumetric flow rate is constant
the continuity rule only applies under what conditions
a short segment, usually a stenosis or narrowing of lumen
FORMULA for volumetric flow rate (continuity rule)
Q= velocity X area
what happens if you decrease the area x2
speed increases X2 to maintain constant flow
how does poiseuilles law contradict the continuity rule
- poiseuille’s law suggests that flow speed decreases with smaller diameters
- continuity rule suggests flow speed increases with smaller diameters
two situations are different because poiseuilles law = entire vessel, continuity rule is the diameter of a short portion (stenosis)
If the AREA of a stenosis is 1/2 the distal vessel what happens to flow speed?
flow speed doubles
if the DIAMETER of a stenosis is 1/2 the distal vessel what happens to flow speed?
flow speed quadrouples
When does flow rate and distal pressure drop significantly with a stenosis?
beyond a diameter reduction of 50% (area reduction 75%)
if you hear a bruit sound what has likely happened?
stenosis due to turbulence distal to stenosis
velocity at a stenosis can tell us what
how much it’s stenosed
what is the Bernoulli effect
a decrease in pressure in regions of high flow speed (velocity and pressure are inversely related)
therefore low pressure at the stenosis because high velocity
what are the conditions of an aneurysm?
there is a decrease in speed at the widening, causing increased pressure
