Quiz 4, Part 1- Hemodynamics Flashcards
As cross sectional area increases, velocity _____
Equation?
decreases
Flow= Velocity x Area Velocity= Flow/Area
Ohm’s Law - What two factors determine blood flow thru vessel?
Equation?
voltage diff and resistance.
Q= (PressureArterial - PVenous) or ∆P= QxR
_____________________
Resistance
According to Ohm, increasing resistance ___ flow
decreases
According to Ohm, increases resistance ___ pressure
increases
Define BP
the force exerted by the blood against any unit area of the vessel wall
Conversion factor from mmHG to cmH20
1mmHg = 1.36cm h20 pressure
Cerebral perfusion pressure
MAP - CVP or ICP (whichever is higher)
What dose Poiseuille’s Law talk about?
Determinants of FLOW
1) Radius*
2) Viscosity
3) Length
4) Pressure Gradient (a.k.a gravity)
According to Poiseuille, flow is ___ proportional to the pressure gradient
directly
According to Poiseuille, flow is ____ proportional to the radius
directly
According to Poiseuille, flow is INDIRECTLY proportional to ____ and ____
viscosity and length
***According to Poiseuille’s law what factor has the greatest impact on the rate of blood flow thru a vessel
Radius to 4th power
If radius is doubled, flow increases by how much? Tripled?
16 fold
64 fold
What is resistance and can resistance be measured directly?
The impediment to blood flow in a vessel.
NO
SVR Formula?
Normal?
SVR= (MAP-CVP) x 80
_________
CO
700-1600
PVR Formula?
Normal?
PVR= (MPAP-PCWP) x 80
_________
CO
100-300
Blood vessels in series =
R total= R1+R2+R3..
The sum of resistances of each vessel
Blood vessels in parallel =
1/R1 + 1/R2 + 1/R3…
Flow thru each of the parallel vessels is determined by
the pressure gradient and its own resistance
If you add another blood vessel what happens to total vascular resistance
decreases
..d/t increase/widening of pressure gradient?
Laminar flow is most related to
Viscosity
Turbulent flow is most related to
Density
Laminar flow - blood near vessel wall is ___, blood in middle is ___
slow, fast
= parabolic nature
What formula predicts laminar vs turbulent?
Values?
Reynolds #
When > 2000, turbulence usually occurs*
<2000- laminar
2000-3000- variable
>3000- turbulent
Reynolds number formula
(density x tube diameter x mean velocity)
________________________________
viscosity
Increasing hematocrit ____ viscosity
increases
HCT= % of blood that is RBCs
Reduced hematocrit causes ___ viscosity, which causes ____ (high or low) turbulence
decreased/ high
because viscosity is inversely related to Reynolds number
Higher viscosity , ___ Reynolds #
decreases #
= more laminar flow/ less tendency for turbulent flow
As blood pressure increases within a vessel.. why does FLOW increase much greater than one would expect?
because of DILATION (arterial resistance decreased) and Sympathetic stimulation (increasing pa-pv gradient)
Flow takes the path of
Least resistance
Whats a predictor of when laminar flow becomes turbulent?
Reynolds #
What are the 3 factors that affect resistance?
Proportional or inversely proportional to resistance?
1) Radius- inversely proportional to 4th power
2) Viscosity- proportional
3) Length- proportional
Vessel RESISTANCE is ____ proportional to radius to the 4th power
inversely
FLOW is ___ proportional to radius to 4th
directly
(Bernoulli) stenosis - Velocity ___ as diameter decreases
increases
SVR is primarily determined by
vessel diameters
When the volume of flow starts to decrease, arterial resistance ___. because the organ is saying I need ____!
decreases , dilates. volume… (doesn’t constrict thinking its a BP problem)
Bernoulli Principle:
______ energy and _______ energy can be interconverted to that total energy remains unchanged
Kinetic energy
pressure energy
