Flashcards in Systemic Circulation Deck (22)
What are the three axes of pressure?
all work together to make 1 direction of flow
what does compliance do in regards to blood vessels?
the greater the volume of fluid, the greater the pressure (since C = V/P)
what happens after injecting fluid in:
with regards to pressure and volume
-no change in vessels (pressure change is infinite, but volume change = 0)
-liquid can leak out of the vessels (volume is infinite, but pressure = 0)
-liquid is contained (V > 0), and pressure builds (P > 0)
what is transmural pressure equal to?
Ptm = P in - P out
how do arterial and venous compliance differ?
venous have increased compliance (steeper V/P)
-at unphysiologically high pressures compliance (for veins, around 50 mmHg) is low
-at low transmural pressures, compliance is extremely high, as the vein becomes fully rounded (initially flat at low volumes)
arterial pressure has a steady compliance from both changes in pressure and volume
what does it mean when blood vessels are distensible?
they can expand and contract depending on the pressure, changing blood volume contained within
what is compliance of most arteries and veins at near operating pressure?
arteries: 2 mL/mmHg
veins: 100 mL/mmHg
how are systemic veins different from arteries in terms of distensibility, volume, and compliance?
8 times more distensible
3 times the volume
24 times the compliance
what does a flat or steep slope mean if:
-volume on x-axis and pressure on y-axis
-pressure on x-axis and volume on y-axis
-x-axis V and y-axis P = slope is compliance, so flat is less compliant, steep is more compliant
-x axis P and y-axis V = slope is elastance, so flat is more compliant, and steep is less compliant
how much blood does a normal adult have in the arterial system, and what is the pressure? what happens i volume drops below 400 mL?
normal amount of blood is 700 mL at 100 mmHg
-pressure falls to zero if volume goes below 400 mL
what does it mean to the blood system when compliance decreases with age?
blood pressure increases with age, because arterial volume and TPR increase
what is the Windkessel effect? what is the consequence?
storage of blood during systole
-the consequence is the maintenance of blood flow during diastole
-conversion of pulsatile flow to steady flow
Windkessel effect in vessels
instead of "on/off" output flow as would be seen in noncompliant tubes, the flow will be high, then once the source is turned off, it will will taper by emptying out what it saved in the pulsatile vessel (pressure remains pulsatile)
how long does ventricular systole and diastole last?
systole: 0.3 sec
diastole: 0.5 sec
creates average 75 BPM
pulse pressure in terms of stroke volume and compliance
PP = SV/C
how is tension related to transmural pressure and radius?
T = P * r
so tension is proportional to both P and r
what variable can promote aneurism enlargement?
tension can promote enlargement of aneurism (arterial bulge caused by weakening vessel wall)
what happens to resistance and flow in rigid vessels as pressure increases?
as pressure increases, resistance stays the same, but flow increases
what is the critical closing pressure?
what happens in hypotensive shock? how does the critial closing pressure change?
major blood loss and related will drop BP until perfusion of organs (flow) is very low
-counteracted by massive vasoconstriction to raise BP (via critial closing pressure)
-it rises from 6 mmHg to 40 mmHg
how do the compliance curves shift in response to hemorrhage?
sympathetic response (contraction of smooth muscle) would lower void volume in an attempt to keep blood pressure up, so the curves would shift to the left