Systemic Circulation

Question 1

What are the three axes of pressure?

Answer 1

hydrostatic pressure
driving pressure
transmural pressure
all work together to make 1 direction of flow

Question 2

what does compliance do in regards to blood vessels?

Answer 2

the greater the volume of fluid, the greater the pressure (since C = V/P)

Question 3

what happens after injecting fluid in:
-zero compliance
-infinite compliance
-finite compliance
with regards to pressure and volume

Answer 3

• 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)

Question 4

what is transmural pressure equal to?

Answer 4

Ptm = P in - P out

Question 5

how do arterial and venous compliance differ?

Answer 5

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

Question 6

what does it mean when blood vessels are distensible?

Answer 6

they can expand and contract depending on the pressure, changing blood volume contained within

Question 7

what is compliance of most arteries and veins at near operating pressure?

Answer 7

arteries: 2 mL/mmHg
veins: 100 mL/mmHg

Question 8

how are systemic veins different from arteries in terms of distensibility, volume, and compliance?

Answer 8

8 times more distensible
3 times the volume
24 times the compliance

Question 9

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

Answer 9

• 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

Question 10

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?

Answer 10

normal amount of blood is 700 mL at 100 mmHg

-pressure falls to zero if volume goes below 400 mL

Question 11

what does it mean to the blood system when compliance decreases with age?

Answer 11

blood pressure increases with age, because arterial volume and TPR increase

Question 12

what is the Windkessel effect? what is the consequence?

Answer 12

storage of blood during systole

• the consequence is the maintenance of blood flow during diastole
• conversion of pulsatile flow to steady flow

Question 13

Windkessel effect in vessels

Answer 13

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)

Question 14

how long does ventricular systole and diastole last?

Answer 14

systole: 0.3 sec
diastole: 0.5 sec
creates average 75 BPM

Question 15

pulse pressure in terms of stroke volume and compliance

Answer 15

PP = SV/C

Question 16

how is tension related to transmural pressure and radius?

Answer 16

T = P * r

so tension is proportional to both P and r

Question 17

what variable can promote aneurism enlargement?

Answer 17

tension can promote enlargement of aneurism (arterial bulge caused by weakening vessel wall)

Question 18

what happens to resistance and flow in rigid vessels as pressure increases?

Answer 18

as pressure increases, resistance stays the same, but flow increases

Question 19

what is the critical closing pressure?

Answer 19

6 mmHg

Question 20

what happens in hypotensive shock? how does the critial closing pressure change?

Answer 20

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

Question 21

how do the compliance curves shift in response to hemorrhage?

Answer 21

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

Question 22

Reynaud’s syndrome

• what is it
• what kind of defect causes Primary Reynauds?
• how do the resistance (or flow) X pressure curves shift?
• what happens during a Reynaud’s attack?

Answer 22

brief episodes of vasospasm triggered by cold or emotional stress

• usually affects fingers and toes
• primary caused by functional defect in vasculature (more common)
• secondary consequence of another disease (more severe)
• shifts resistance (or flow) X pressure curves to the right
• digits turn white (ischemia), blue (deoxygenation), then red (reperfusion), and blood flow returns with discomfort