Hemodynamics Flashcards
what can blood flow through an organ be considered (circuit)
blood flow through a series network
how is blood flow to different organs controlled in the absence of difference in arterial blood pressure?
differences in resistance within the organs dictates the difference
which vessels have the largest resistance? what implication does this have to the overall resistance of an organ?
arterioles
means that the overall resistance in an organ is determined by the resistance of the arterioles and therefore their radius
how is blood flow controlled in organs?
by varying the tension in the smooth muscles of the arterioles
what is the overall resistance to flow through the circulation called? what is the equation?
total peripheral resistance
1/TPR=1/R1+1/R2+1/R3…
what is the equation relating TPR to friction?
TPR=frictional losses/Cardiac output
what equation relates TPR to MAP (mean arterial pressure)
MAP=COxTPR
what can we assume the central venous pressure is during calculations?
zero
describe the relationship between flow and driving pressure?
it is linear and beginning at zero. the slope of each line equals 1/R
how can one change the flow vs pressure graph?
by changing he resistance by changing the pressure of the system and/or the cardiac output
what is the normal value of TPR at rest?
1.2 PRU
what is the reynolds number and what does it determine?
Re=disruptive forces/cohesive forces
describes when flow is turbulent or not
what values of reynolds number constitute which type of flow?
Re3000 is turbulent flow
what is viscosity and what does it determine?
measure of intermolecular attractions in the liquid and it determines the steepness of the velocity gradient
when does laminar flow break down? what happens at this point?
when the velocity reaches a critical point
the flow depends less on pressure gradient because the effective resistance increases
what is the breakdown of laminar flow called? which flow has less flow for the same change in pressure and what does this demonstrate?
turbulent flow
there is less flow in turbulent flow (loss of kinetic energy)
how can clinicians detect turbulent flow? what is this called?
laminar flow is silent but turbulent flow generates sound (ascultatory sounds)
what are murmurs?
audible sounds due to vibrations in heart or vessel walls
what are “innocent” systolic murmurs caused by?
when cardiac output increases during exercise causing turbulence in the aorta during systole
what are korotkoff sounds?
the sounds that are used during blood pressure measurement
what causes abnormal murmurs?
aortic or mitral stenosis causing regurgitation
why are thrombi more likely with turbulent flow?
because the arterial wall may be damaged by turbulence
what is the mean circulatory pressure? what is its value?
the equilibrium pressure that would result if the heart stopped beating.
7 mmHg
how does gravity affect blood pressure?
it either adds to or subtracts from the pressure generated by the heart depending on the relative position to the heart
how is the gravitational pressure on arteries counterbalanced?
by the gravitational pressure at the same level in the corresponding veins
at what level should blood pressure be taken and what happens if it is taken below this point?
it should be taken at the level of the heart because below this there will be an overestimation of blood pressure
although gravity does not affect the driving pressure on the blood, what does it affect?
it affects the distribution of blood throughout the system and therefore affects the transmural pressure
what changes the energy in a vessel?
applied pressure, changes in gravitational energy and changes in velocity
what is static pressure? describe its properties?
static pressure is present whether the blood is moving or not. composed of applied lateral pressures in wards from the other fluid and is outwards against the vessel wall.
what is dynamic pressure? describe its properties
dynamic pressure is due to kinetic energy and most pressures are in the opposite direction than static pressure. there is pressure inwards from the walls and laterally in the direction of flow
what happens to dynamic pressure as velocity decreases? as the vessel radius narrows?
velocity decreases, dynamic pressure becomes a smaller fraction of the total
as vessel radius narrows dynamic pressure increases
how does dynamic pressure change when radius is decreased by half?
it increases four fold
when does dynamic pressure in the aorta become important?
when cardiac output increases
how does the total and lateral pressure compare with a high velocity fluid vs a slow fluid in a vessel?
the total pressures are the same, but a high velocity vessel has lower lateral pressure
in which direction in relation to flow is the pressure in a vessel highest?
in the direction that flow is coming from
how is sheer stressed created?
flowing blood on the endothelial wall directed along the long axis of the vessel
what is sheer stress proportional to?
viscosity and sheer rate (rate at which the axial velocity changes from the wall to the lumen)
describe the velocity profile in a rigid cylindrical tube
it is parabolic with the outermost layer having zero velocity because of friction
what is the axial velocity and how does it relate to mean velocity in a vessel?
it is the maximal velocity because it has minimal frictional retardation
it is twice the mean velocity
how does stenosis affect flow?
there is more turbulent flow near the initiation of narrowing.
what is the direct effect of atherosclerosis on sheer stress and flow?
causes local increase in velocity and increases dynamic pressure and decreases lateral pressure. this increases turbulence and changes sheer stress
if the lateral pressure decreases too much do to narrowing of an artery, what will happen? what is a possible complication from this?
the artery will collapse and the flow will stop momentarily
this could result in the ruure of a plaque and the formation of emboli
