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Veins are ____ times more distensible than arteries
What is vascular tone?
the normal semi-contracted state blood vessels exhibit
How does the distensibility of a tube affect flow?
increased distensibility allows more flow for a given perfusion pressure
Does a small distensible blood vessel exposed to high pressures exhibit more or less resistance than the same vessel exposed to lower pressure?
As the pressure increases the radius of the vessel increases which decreases resistance and increases flow
What is tension?
the internal force generated by a structure
What is the formula for LaPlace's Law for for cylinders?
T = P x R
As a structure expands, the tension (force in the wall of the structure) increases or decreases?
What does Laplace's Law mean for the thickness of walls of small and large vessels?
In order to withstand the same pressure, a vessel with a large diameter must have thicker walls
How does LaPlace's Law relate to the Frank-Starling law?
Greater the filling pressure = greater the tension
LaPlace = increased tension with increased filling
Frank Starling = increased tension = increased stroke volume
How do you calculate vascular distensibililty?
(increase in volume)/(increase in pressure x original volume)
So if volume increases by 1 ml and pressure increases by 1 mmHg and original volume was 10 ml, the distensibility is 10%
How does the same volume fit in the systemic circulation as the pulmonary circulation?
Pulmonary vasculature is 6x more distensible than systemic vasculature
What is vascular capacitance or compliance? What two things contribute to compliance?
the total quantity of blood that can be stored in a given portion of the circulation for each mmHg of pressure
Distensibility and volume
Are the veins more or less compliant than arteries?
24x more compliant
What happens to the compliance of our vessels as we age?
They become stiffer, less distensible, and less compliant so to hold the same volume, the pressure will increase much more
What is delayed compliance or "Stress-relaxation?"
- a vessel has an initial increase in pressure when exposed to an increase in volume but the smooth muscle eventually stretches and the pressure returns to baseline.
- The reverse is true for a decreased pressure.
What does the dicrotic notch (incisura) represent?
produced when the aortic valve closes which causes a brief period of retrograde flow from aorta back toward the valve that briefly causes aortic pressure to be less than systolic pressure
What is the formula for MAP?
(systolic x diastolic x diastolic) / 3
What 2 factors affect pulse pressure?
- 1: stroke volume output
- 2: compliance of arterial tree
What 2 things contribute to the decreased presence of pulse waves in the smaller arteries?
- 1: increased resistance
- 2: increased compliance
Why is the pulse pressure wider in the large arteries than in the aorta?
aorta is more compliant
What is the driving force for blood flow in arteries?
mean arterial pressure
How does arteriosclerosis change your pulse pressure?
increases (d/t decreased compliance)
How does aortic stenosis change your pulse pressure?
decreases (d/t decreased outflow)
How does a patent ductus arteriosis change our pulse pressure?
increases - increased systolic, slightly decreased diastolic
large portion of blood pumped from LV flows back into pulmonary artery
How does aortic regurgitation change your pulse pressure?
increases - diastolic may approach zero, systolic elevated
blood pumped from LV flows immediately back into LV.
No dicrotic notch because no aortic valve closure.
What are 5 things that narrow pulse pressure?
- - tachycardia
- - severe aortic stenosis
- - constrictive pericarditis
- - pericardial effusion
- - ascites
What is a normal MAP?
70 - 110
The spleen is a reservoir for what 2 things?
blood and RBC's
How does an increased right atrial pressure affect venous pressure?
it causes blood to back up into the venous system which increases venous pressure
What is a normal CVP? What is the low limit?
0. Lower limit is -3 to -5
What 4 things increase RAP?
- - increased blood volume
- - increased venous tone
- - dilation of arterioles
- - decreased cardiac function
What is the pressure in legs when standing?
If abdominal pressure increases, what has to happen to the venous pressure in the legs? why?
it also has to increase to overcome abdominal pressure and flow back to heart
Why is there a risk for venous air embolism during a craniotomy/opening of sagittal sinus?
veins inside the skull are negative pressure because they are in noncollapsible chamber