1,2- Overview of Circulation and Hemodynamics Flashcards
arteries
for high pressure to transport to organs
arterioles
for controls and distribution of flow
capillaries
to exchange nutrients, electrolytes, hormones, etc.
have the largest overall cross sectional area, in parallel with one another. blood moves the slowest here so you have time for exchange of nutrients/O2 and CO2
venules
to collect blood from the capillaries
veins
to transport of blood back to heart
Order of systemic circulation
arteries -> arterioles -> capillaries -> venules -> veins
are pulmonary and systemic circulation in series or parallel?
series but within each are parallel elements so blood is distributed to various vascular beds independently depending on what the tissues needs are. also means that disruption in blood supply to one part of circulation doesnt mean it will disrupt everywhere
is arterial or venous pressure higher?
arterial but most of the blood is in the veins (venous side is more compliant)
100ml of blood is what makes the arterial pressure
explain the pulsatile nature of the heart
pressure is most pulsatile near the “pulsing” heart. you have the largest pressure drop at the arterioles. Pressure overall drops as blood moves from arterial to venous sides of circulation and pressure becomes less pulsatile.
bloodflow in an individual vessel segment is determined by
inflow-outflow pressure
relationship between pressure/flow/resistance
change in pressure = flow x resistance
flow is always in the direction from high to low pressure
blood pressure
bp = force exerted by blood / area of vessel wall
Conductance
measure of blood flow through a vessel for a given pressure difference. Simply the inverse of resistance
1/Resistance
C~d^4 (varies in proportion of the 4th power of diameter)
Poiseuille’s Law
F= (deltaP) (Pi) r^4/ 8 (viscosity)(length)
Note: vessel radius plays greatest role in determining rate of blood flow through a vessel
Ohms law with respect to the heart
F = (deltaP) / R
laminar flow
steady state flow streamlines
hematocrit
% of cells in blood, pressure must go up to surpass viscosity factor
normal men ~42%
normal women ~38%
anemia < normal
polycythemia > normal
Calculate resistance in series and parallel
series-> add them and the total is greater than the largest
parallel-> add 1/each R together and the total is less than the smallest
systolic vs. diastolic pressure
systolic pressure- each time the heart beats it ejects blood which increases arterial bp to peak
diastolic pressure- as vessels empty, blood moves from arteries to veins the pressure falls
pulse pressure
systolic pressure - diastolic pressure
how to increase systolic pressure
goes up if vessels get stiffer and harder
how to increase diastolic pressure
goes up if you have an elevated HR
arterial pressure contours
- stroke volume ejected into arterial tree (how much blood is pumped out of heart)
- force of contraction/how hard heart is pumping (determines peak systole)
- heart rate determines time of diastolic runoff (longer time between beats the greater the runoff of the ejected volume into the venous circulation, and therefore the lower the diastolic pressure)
- arterial vascular resistance (a greater resistance reduces the runoff of blood into the veins before the next beat and therefore diastolic pressure is high)
what happens during aortic regurgitation
ejected stroke volume flows back inot the ventricle (regurgitation) during diastole; with an A-V shunt blood flows directly into the venous circulation. Both lower diastolic pressure.
what happens to a pressure vs time curve when you have arteriosclerosis
arteriosclerosis- stiffining of aorta
the graph just gets taller
what happens to the pressure vs time curve when you have aortic stenosis
stenosis- valve doesnt open all the way (closure of the aortic ring)
LV pressure is very high here and the graph becomes much shorter and flatter
what happens to the pressure vs time curve when you have patent ductus arteriosus
low R for blood to come back out of aorta (high systolic and low diastolic pressure)
graph gets taller and the little step near the top moves further down
what happens to the pressure vs time curve when you have aortic regurgitation
it becomes a tall hill without any little step near the systolic pressure top
mean arterial pressure
average of all pressures integrated and averaged over time
approximately equal to DBP + 1/3 Pulse
how do veins work
can constrict and dilate, thus serving important blood storage function
venous “muscle pumps” propels blood foward to return blood to heart (smooth muscle)
what determines pressure in veins
right atrial pressure- regulated by balance between ability of right heart to pump out blood and the tendency for blood to flow from the peripheral veins into the right atrium
*heart is responsible for setting final lowest pressure in venous pressure (if it can’t then you have edema)
blood reservoirs
venous side of circulation plays “blood storage role”
spleen liver large abdominal veins venous plexus of skin heart lungs
factors that tend to collapse veins entering thorax
- large veins have little resistance
- veins that enter thorax are compressed at certain points so flow is impeded
- intrathoracic pressure is negative which distends veins and atmospheric pressure collapses neck veins
- abdominal veins are compressed by organs and intra-abdominal pressures
gravitational/hydrostatic pressure
weight of blood in column causes greater pressure in the longer column of fluid cause of gravity
blood doesnt normally balloon out of veins b/c smooth muscle (skeletal muscle kinda does) contracts to squeeze it back to the heart. Veins are distensible so they can get larger and larger
gravitational pressure = density of blood x acceleration due to gravity (980) x vertical distance above or below heart
why is it bad to stand absolutely still for 15 mins-ish
with no leg movement, elevated pressure in legs raises capillary pressure (fluid filters out) and the leg swells
you can lose 10-20% of blood volume in 15 mins w/o moving
