Hemodynamics Flashcards
blood flow
Q (L/min) = velocity * cross sectional area
A = pie r^2
equation of continuity
system is closed amt of blood flowing is constant
Qa=Qb=Qc or vA=vA=vA
Poiseulle’s equation
describes fluid flow through rigid pip
Q = (diffPpier^4) / (8lengthviscosity)
relationship bet Q and P
Q is proportional to diff P
no pressure no flow = heart failure
relationship bet Q and vessel radius
Q proportional to r^4 small change in dia = great change in flow resistence arterioles so, 2r = 16x inc in Q and 1/2r = 16x dec in Q
relationship bet vessel length and Q
Q proportional to 1/L
irrelevant bc w cant change it
greater dist = greater R = less flow
relationship bet viscosity and Q
Q = 1/viscosity
more viscous greater resistance to flow
life at high altitudes
inc hematocrit to comp for dec O2 availability
inc RBC -> inc viscosity = dec Q
polycythemia vera
overproduction of red blood cells
increased viscosity decreased flow
severe dyhydration
decrease of plasma
thus inc viscosity and dec flow
sickle cell anemia
reduce pliability of RBCs - increase resistence, increase apparent viscosity , so decreases flow
resistence in series
Rtotal= R1+R2+R3 etc
1+2+3=6
resistence in parallel
decreases total R
change one R doesnt affect others or total R
Resistance is at resistance arterioles (capillaries don’t contribute)
1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc
=o.55
systemic vascular resistance (SVR)
total peripheral resistance (TPR)
sum of all resistances that lie bet aorta and vena cava
TPR/SVR = (mean art P - central venous P) / CO
normal; 15-18mmHg
pulse pressure =
PP = SystolicBP - DiastolicBP
mean arterial pressure =
MAP = DiastolicBP + (PP/3)
note; this is not an average bc the heart spends more time relaxed (2/3) than contracted (1/3)
shock and TPR/SVR
most shock = Increase in TPR
septic shock = lrg Decrease in TPR
cardiogenic shock
inc Preload, dec CO, inc SVR
hypovolemic shock
dec Preload, dec CO, inc SVR
distributive/septic shock
dec/normal Preload, and CO change, Dec SVR
obstructive shock
inc Preload, dec CO, inc SVR
pulmonary embolism shock
dec Preload, dec CO, inc SVR
deviations from Poiseuille’s Law
1) laminar vs. turbulent flow
2) viscosity changes w velocity
3) compliance of blood vessels
streamline/laminar flow
velocity center>velocity at edge
flow:pressure
fluid in middle flows the fastest
turbulent flow
chaotic velocities (as velocity inc pattern becomes unstable and breaks down into turbulence)
flow : sqr root of Pressure
so, greater P require to push same amt of blood (to get same amt of Q)
Reynolds number
dimensionless number analyzes flow through tubes
Nr > 2000 = turbulent flow
Nr = (veldiadensity) / viscosity
so ratio of;
inertial forces (disrupt laminar flow)
to, viscous forces (stabilize laminar flow)
murmurs
the sounds of turbulent flow
relationship between viscosity and velocity
viscosity - 1/velocity
low velocity gets gunky
speed up, breaks those interactions - less viscous (more like water)
relationship of compliance
compliance = how much they dilate - the change in volume for a given pressure change
veins - highly compliant
= change in Vol / change in Pressure
Poiseulles equation
Q = (diff P* pie * r^4) / (8 * length * viscosity)
fluid flow through a rigid pipe
