15. Hemodynamics & Systemic Circulation Flashcards
what is the pressure in the As after the aorta
highest
= stressed volume
what is the pressure in arterioles compared to As
moderate P
where in the circulatory system can you change resistance to control flow
arterioles
Sm M contract to control flow by changing resistance
what determines ther degree of perfusion in capillaries
constriction/dilation of arterioles
what is the P in venules
low P
(large vol)
how can venules control BP
contract to move more blood to arteries to increase BP
what are characteristics of Vs
large capacitance
low P, large vol = unstressed vol
what are characterisitccs of capillaries
lare cross-sectional area
single endothelial lining
nutrient/waste/gas exchange
what area of circulation has to largest area
capillaries
where is blood volume least
aorta/As/arterioles
relative to the parts of circulation, what is the area and BV of the Vs
large A (but smaller than capillaries)
large BV
how does area contribute to velocity of blood flow
inverse relationship (increase A –> decrease velocity)
V = Q/A
(calculated single vessel or total summed cross sectional A of parallel circuits)
compare the velocity of the aorta & capillaries
aorta - high velocity ( bc small area)
capillaries - low velocity ( bc large crossectional A)
what is the flow from aorta to systems
flow is consistent, however the flow is divided btn the systemsl like ….
cerebral = 15%, coronary = 5 %, etc
how does flow change throughout the system
the percent division btn systems change based on hormones/activity
like… exercise - more blood sent to MSK than GI
*- based on arteriole resistance*
how does pressure gradient and resistance contribute to flow
flow (Q) = pressure gradient/R
pressure gradient directly related to flow
R inversely related to flow
how do you calculate cardiac output with pressure and resistance
=(arterial pressure - venous pressure) / total peripheral resistance
(=pressure gradient/R)
how is Resistance calculated
change R w/
- viscosity - direct relationship
- length of vessel - direct relationship
- * vessel radius * = most significant & inverse relationship
how is vessel radius controlled & what is the purpose
hormones or local factors
change resistance to regulate BP and match blood flow to metabolic needs
how do you calculate vascular resistance for vessels in series
add the resistances
(longer the tube - more resistance)
how do you calculate vascular resistance for vessels in parallel
1/R(total) = 1/R1 + 1/R2 + etc
total resistance decrease
when does laminar flow change to turbulent flow
high velocity
large cross sectional area
heavy density or
low viscosity
>2000 Reynolds number (=transition)
how does you calculate reynolds number
increases w/ density, diameter, velocity
decrease with viscosity
what can turbulent flow lead to
sound (bruits)
lesion (arteriosclerosis)
what is laminar flow
high velocity in middle &
zero on the walls (bc increased viscosity on walls)
ideally = parabolic
what is complaince
how easy it is for a vessel to expand (–> holds more volume)
change in vol/change in pressure
what has a larger compliance Vs or As
Vs
easiest to stretch –> so hold larger volume at lower pressure
what is the compliance for As
low
harder to expand –> so need larger P to hold low volumes
what happens to compliance when Sm. M of Vs contract
decrease compliance –> decrease volume (shift volume from V to A)
so in A increase P and volume
what happens to complaince with aging As
walls get stiffer –> decrease compliance
so you need higher Ps to hold same amount of volume
why do you have pulsatile pressure in aorta
compliance and distension during ejection and recoild during diastole
-lost by arterioles
what is the pulse pressure dependent on
atrial compliance
why is the pulsitile pressure higher in the large As compared to the aorta
echo effect
-waves bouncing back fron small As and arterioles
where is pulsatile pressure lost
arterioles
what happens to P in the arterioles
huge decrease bc high resistance to flow
at end around 30 mm HG
how is systolic pressure and diastolic pressure reported clinically
systolic = greatest P in large A
diastolic = lowest P in large A
why is mean pressure closer to diastolic P
spend more time in diastole than systole
= diastolic + 1/3*pulse
how do you calculated pulse pressure
systolic - diastolic
what happens if you have a decrease in compliance of arterials
increase pulse P
-increased systolic P & diastolic stays same (but could decrease)
what happens to pulse P in arteriosclerosis
decrease compliance
increase pulse P
what happens to pulse P in aortic stenosis
decrease pulse pressure bc decreased SV
what happens to the pulse pressure (and its graph) if R is increased
shift the entire graph up
*no change in shape*
What is the clinical significance of an increased left atrial pressure?
indicative of heart failure or decreased left ventricular output
What is the pulmonary wedge pressure directly proportional to?
left atrial pressure
