Hemodynamics Flashcards
most of the blood in our body is where
venous side
vascular resistance is greatest at what level
arteriole level
arteries vs. veins (which one is more compliant/distensible?)
veins
distribute blood flow, control bp, exchange solutes/fluids
blood vessels
collect fluid and proteins in interstitial spaces and return to circulation
lymphatics
why is it important to maintain bp
so blood can perfuse and supply organs
force exerted by the blood against the vessel wall
pressure
diastolic - systolic pressure
pulse pressure
refers to mean arterial pressure (MAP); dictates perfusion of the systemic organs
blood pressure
CO x SVR=
blood pressure
MAP=
DP + 1/3 PP
OR
(add twice the DP to the SP)/3
normal MAP
85 mmHg
increased arterial rigidity increases with what
age
as we age, natural arterial sclerosis occurs and vessels become stiffer and less compliant causing and increase in what
BP
PP
SP
when a person stands up, all the blood rushes to feet but what is maintained
perfusion gradient (organs are still getting their needed blood)
total amount of fluid moving past a point over time
flow
speed of fluid
velocity
what happens when there is an increase in cross sectional area at site of capillaries
speed and pressure of blood slows down and resistance increases
parabolic velocity profile of blood; blood travels fastest in the center (axial streaming)
laminar flow
the drag between individual layers; increases with increasing amount of RBC’s
viscosity
this is important for maintaining vascular homeostasis; makes it less likely for blood cells to stick to the vessel wall
shear stress profile
where velocity increases, pressure falls
Bernoulli effect
non-invasive way to measure blood flow and detect reduced perfusion; probe on skin detects sound wave from blood vessels
Doppler US
invasive way of measuring blood flow that is used in surgery; 2 electrodes placed on vessel; measures emf of charged particles in blood
electromagnetic flowmeter
2 main determinants of vascular resistance
vascular diameter
blood viscosity
important in controlling blood flow to organ beds and bp
vascular resistance
how to calculate blood flow
Ohm’s law:
flow= change in pressure/resistance
increase viscosity= increase in
resistance
increase in diameter= decrease in
resistance
small changes in arterial radius cause ______ changes in resistance
large changes (remember r^4)
in a series circuit, where will pressure increase and decrease when resistance is applied (water hose)
pressure will decrease downstream and increase upstream of added resistance
in parallel circuits, what is the distribution of pressure
the parallel branches all have the same pressure
the whole network of vascular resistors can be reduced to what
a single resistor
defined as a single resistance for the whole body (total resistance of entire systemic circulation)
systemic vascular resistance (SVR) or total peripheral resistance (TPR)
amount of blood pumped out of heart per minute
cardiac output for the heart
= stroke volume x HR
CO (heart)
defined as total blood flow of the body
cardiac output (circulation)
in circulation, cardiac output=
MAP/SVR
mean arterial pressure/systemic vascular resistance
increase SVR=
increase in arterial pressure
constriction of 1 or few arterioles has what impact on MAP
little impact
constriction of many arterioles has what impact on MAP
large impact
Newtonian fluids (constant viscosity)
water and plasma
viscosity variable (non-Newtonian); due to # of RBC’s
whole blood
can cause sludging and reduced flow
low net perfusion pressure (very low bp)
aligning of RBC’s in center of vessel can reduce what
viscosity
main determinant of blood viscosity
hematocrit
normal hematocrit % for males
45%
normal hematocrit % for females
40%
below normal hematocrit is known as
anemia
why is 40-45% optimal hematocrit
because at the percentage, oxygen delivery is optimal
control of vascular diameter is the primary mechanism for rapidly altering what in the body
resistance
blood forced through a vessel too fast (no longer parabolic)
turbulent flow
increasing velocity or decreasing viscosity can lead to what
turbulent flow
determines if flow is turbulent; >2000
Reynold’s number
atheroslerotic plaques or coarctation and anemia can lead to what
turbulent flow (bruit)
causes rushing sounds around affected valve (murmur)
Valvular stenosis or insufficency
force acting to pull or tear open the vessel wall
wall tension
tension= transmural pressure x _____
r (radius)
wall tension is highest where
aorta
high pressure and large diameter cause increase in what
wall tension
