Module 8 : Hemodynamics Flashcards
what is hemodynamics
- study of blood flow in the circulatory system
what is the circulatory system comprised of and what type of circuit is it
- closed circuit
- heart, arteries, capillaries, veins
what is the venous heart
- contracting muscles that help pump blood back to the heart especially in the lower extremity
what is blood composed of
- plasma
- erythrocytes
- leukocytes
- platelets
what is the hematocrit
- the amount of blood that is made up by cells
in which portion of the circulatory system is the most blood contained
- veins
what type of flow is seen in the capillaries
- low volume and velocity
what is required for any fluid to flow
- pressure different / gradient
what results from an increase in the pressure
- increased flow rate
what is a pressure gradient
- pressure difference divided by the distance between two pressure locations
what is the volume flow rate
- volume of blood passing a point per unit time
what happens to the volume flow rate if the pressure gradient increases
- flow increases
what happens to volume flow rate is the resistance increases
- flow decreases
what is pouselles equation for resistance
- R = 8 x length x viscosity / ii x radius ^4
what will increase resistance to flow
- longer length
- increased viscosity
- decreased radius
what factor will have the greatest effect on the resistance to flow
- change in radius because of exponent
what are the 5 different flow patterns
- plug
- laminar
- jet
- disturbed
- turbulent
characteristics of plug flow
- seen at opening of large vessels
- all RBCs travelling at same velocity
characteristics of laminar parabolic flow
- most common
- RBC move in concentric layers with the ones at the centre moving the fastest
characteristics of jet flow
- seen when there is significant reduction in diameter
- velocities within narrowing are the fastest
characteristics of disturbed flow
- occur naturally with tapering curves and bif
- not all layers moving in laminar fashion
characteristics of turbulent flow
- type of flow just past stenosis
- flow velocities vary in velocity and direction
- not normal except near the heart
what is Reynolds number
- can predict the onset of turbulence in a vessel
what is the number that must be exceeded for turbulence to occur
- 2000
what is the continuity rule
- in the presence of a stenosis the volume of flow must stay the same proximal, within and distal to stenosis
what must happen to the velocity of blood is a stenosis reduced the vessel diameter to less than 50%
- velocity must double within stenosis
what is Bernoulli describing
- pressure and energy must also remain the same through a vessel with a. stenosis
what is Bernoulli’s principle
- at a stenosis a pressure drop is necessary for the fluid to accelerate through the stenosis and decelerate past stenosis
- pressure/ potential energy is converted to kinetic energy at the stenosis then back to potenital after stenosis
what is the simplified Bernoulli equation
- P = 4(v^2)
what is tardus parvus flow
- flow afer a stenosis where there is a drop in acceleration time and PSV
- stenosis detracts from pressure gradient that was created by the heart
what is the windkessel effect
- continued forward flow in diastole because of the elasticity of the vessel walls contracting to its original diameter
what can cause flow reversal in the vessels other than disease
- the pressure wave along the walls of the vessel travels faster than the blood
- when wave reaches en dog arterial system there is a reflected wave that causes the vessel to expand and contract against blood flow
