Hemodynamics Flashcards
hemodynamics
blood movement; the study of blood flow in the circulation
what kind of reservoir are systemic veins
volume reservoir
high compliance to expand and contract to meet demands
contraction of veins pushes blood towards heart –> increases venous return
what kind of reservoir are systemic arteries
pressure reservoir
low compliance –> greatest point of flow
what type of vessels are the major regulator of vascular resistance
arterioles
what is blood flow
the displacement of volume of blood per unit time
what does it mean that blood flow is parabolic
fluid molecules on the outside move slower than those on the inside
outside molecules have friction with the vessels wall (slow)
inside molecules “slip” against the other fluid layers (fast)
ohm’s law
pressure gradient = blood flow x resistance
deltaP = Q x R
what are the two factors affecting blood flow (according to ohm’s law)
pressure difference and vascular resistance
pressure difference & blood flow relationship
increase deltaP = increase blood flow
blood flows from high to low pressure –> greater pressure difference = stronger gradient –> faster flow
can you change the pressure gradient in order to alter blood flow
NO - pressure gradients stay constant at a particular location
what can you change to alter blood flow
resistance
vascular resistance
friction of blood as it passes along the endothelium
how does resistance affect flow
increase R = decrease flow
poiseuille’s law
predicts blood flow based on the radius of the vessel
Q = (deltaP x pi x r^4) / (8 x n x L)
how does radius affect flow
increase radius (vasodilation) = decrease resistance = increase flow
decrease radius (vasoconstriction) = increase resistance = decrease flow
viscosity
“slipperiness” of blood vessels
lower viscosity = more slippery = sharper parabola (faster central flow)
how does viscosity affect flow
increase viscosity = decrease flow
decrease viscosity = increase flow
how does length of the vessel affect flow
blood flow slows along the length of the vessel due to friction
increase length = decrease flow
decrease length = increase flow
Reynold’s number
measures the point at which blood flow increases beyond laminar flow and becomes turbulent (critical velocity)
critical velocity
the speed at which blood flow transitions from laminar to turbulent
aortic pressure
the potential energy available to move blood
how does aortic pressure change across arteries
minimal change from aorta –> arteries
increase pressure from arteries –> arterioles (high resistance vessels)
mean arterial pressure
average pressure in the arteries during the cardiac cycle
MAP equations
MAP - CVP = CO x SVR
(CVP is negligible)
MAP = CO x SVR
MAP = (SBP + 2xDBP) / 3
modified Bernoulli’s equation
estimates pressure gradients using velocity of blood across a narrowed region
deltaP = 4 x V^2
how does velocity affect pressure gradient
narrow vessels = increased velocity = increased pressure difference
wide vessels = decreased velocity = decreased pressure difference
how does Bernoulli’s equation apply to stenotic valves
aortic stenosis –> left ventricular pressure becomes significantly INCREASED compared to the pressure within the aorta (on other side of stenotic valve) –> increased velocity –> increased pressure gradient
windkessel effect
recoil of the aortic wall during diastole to release blood that was stored during diastole
allows perfusion to maintain throughout diastole
pulse pressure
palpable pulse; the difference between systolic and diastolic blood pressure
hyperdynamic pulses
bounding
occurs with increased difference between systolic and diastolic BP
(increased systolic or decreased diastolic or both)
ex. aortic regurgitation
hypodynamic pulses
weak/thready
occurs when decreased difference between systolic and diastolic BP (decreased systolic or increased diastolic or both)
ex. aortic stenosis
what is pulse pressure influenced by
heart rate and stroke volume
perfusion pressure
blood flow directed to perfuse organs
ALL organs receive the same perfusion pressure
how do organs alter local blood flow based on needs (since perfusion pressure is the same to all organs)
changing local arteriole diameter
allows organs to maintain steady blood flow despite changes in systemic BP
auto regulation of local blood flow
local response to changes in systemic perfusion pressure by changing local vascular resistance
occurs within a range of systemic BPs
systemic vascular resistance (SVR)
total peripheral resistance; the net resistance of entire systemic circulation
what are surrogate measures of SVR
blood pressure/MAP
vessels arranged in series
vessels arranged one after the other
total resistance = R(1) + R(2) + … etc
vessels arranged in parallel
vessels arranged as parallel branches
1/total resistance - 1/R1 + 1/R2 + … etc
which vessel arrangement reduces total resistance
parallel
how does resistance change as blood moves from arteriole to capillary
small radius so you would EXPECT resistance to increase as blood moves from arteriole –> capillary
BUT
capillaries are arranged in parallel so resistance decreases from arteriole –> capillary
arteriole function
gate keepers - largely control flow to specific tissues by changing vascular resistance
pulmonary vascular resistance
1/10 systemic vascular resistance
able to accommodate increases in flow from increased CO to lungs and pressure by recruitment and distention of capillaries
capillary recruitment
opening of additional capillaries to accommodate increased flow
capillary distension
widening of capillary walls to accommodate increased flow
