Chapter 8 - Arterial hemodynamics Flashcards
Hydrostatic pressure equals
- rho g h
Specific gravity of blood
1.056 g/cm3
Conservation of energy based on what principle
Bernoulli’s principle
Potential energy in blood
P + rho g h
Kinetic energy in blood
1/2 rho v2
Most common loss of energy in blood as it moves
heat
Ways of energy loss in flowing blood
1) viscous loss - friction 2) inertial loss - change in velocity/direction
Factor that dictate viscosity in blood
Hematocrit
Poisseuille’s law
EQUATION AFTER FIGURE 8.1
Resistance contribution by arterioles, capillaries and medium-sized arteries and veins
arterioles + capillaries = 60% medium sized arteries = 15% veins = 10%
Average blood flow in the human leg
300-500 ml/min
Blood flow to LE muscle
2 ml/100g/min
Exercise-induced increase in LE blood flow
5-10x
Triphasic blood flow explained
1) systolic pulse 2) reverse due to high resistance of arterioles 3) forward flow in late diastole
Boundary layer
portion of fluid adjacent to tube wall
Boundary wall separation key points
1) low shear stress 2) formation of plaques 3) intimal thickening
Vascular impedance definition
Resistance or opposition of peripheral vascular bed to pulsatile blood flow
Inertial energy losses across stenotic area due to two effects
Contraction effect - at entrance Expansion effects - at exit of stenotic segment
Critical stenosis definition
Extent of arterial narrowing to produce significant reduction in blood pressure or flow
Three components of a collateral system
1) stem arteries - large distributing branches 2) midzone - small intramuscular channels 3) reentry vessels
Collateral vs native peripheral bed difference in resistance
Collateral resistance is fixed does not change flow with exercise
Thickness of pseudointima after implantation of prosthetic graft
0.5-1 mm decreases inner diameter of grafts
Tangential stress calculation
stress = pressure x radius / thickness
