Hemodynamics Flashcards
Formula for Viscosity
Shear Stress / Shear Rate
What happens when there is friction in blood vessel?
Flow is fastest at the center, slowest at the wall
Poisseuille’s Equation
Q = Pi r^4 (P1 - P2) / 8nL
Q= Volume flow per unit time (cm3/sec) (P1-P2)= Pressure Gradient R = Radius n = Viscosity (dyne-sec/cm^3) L = Length of tube (cm)
Ohm’s Law
Q = P1-P2 / R
Systemic Vascular Resistance Equation
SVR = 80 x MAP-CVP/CO
Pulmonary Vascular Resistance Equation
PVR = 80 x MPAP-PCWP/CO
MPAP: Mean Pulmonary Arterial Pressure
PCWP: Pulmonary Capillary Wedge Pressure
Fahreus-Lindqvist Effect
Solid particles are not homogenously distributed, RBC occupy middle or fastest layer forming single file
What is Assumption #2?
Why is it false?
The liquid does not slip at the wall
Blood vessels have heparin acting as a slippery coat
Assumption #3?
Why is it wrong?
Flow is laminar.
Flow is not laminar, it is fastest at the middle than at the side
Reynold’s Number
Re = pvD/n
p = Fluid Density V = Velocity D = Diameter n = Viscosity
Reynold’s Number For:
- Laminar Flow
- Turbulent Flow
- Transitional
- Re < 2000
- Re > 3000
- 2000 < Re < 3000
Disturbance of laminar flow usually occurs here
Bifurcation of blood vessel
Most common plaque location
Carotid Sinus
Assumption #4?
Why is it wrong?
Rate of flow is constant
Flow of blood is pulsatile, not continuous
Assumption #5?
Why is it wrong?
The tube is long compared to the region studied.
It’s not, this is the only correct assumption
