Biomechanical Properties of Blood Vessels Flashcards
What are the 3 layers of a blood vessel wall?
tunica intima, tunica media, tunica adventitia
What are the characteristics of tunica adventitia?
increase in collagen, no elastin, amounts remain equal
What is the trend of % composition between SMC, elastin, and collagen?
- SMC: higher % towards smaller size
- elastin: % remains the same
- collagen: higher % towards larger size
The thickness and composition of each lary vary according to what?
vessel and diameter
Large arteries contain what?
thick media layer and high amount of elastin
What is the trend of elastin in small arteries?
amount of elastin decreases
Veins contain what?
thinner media layer and less amount of elastic tissue
How does pressure change in the left heart during a cardiac cycle?
- AV valve opens
- aortic valve closes
- aortic valve opens
- AV valve closes
What is diastolic blood pressure (Pd)?
lowest arterial pressure
What is systolic blood pressure (Ps)?
highest arterial pressure
What is pulse pressure (PP)?
Ps-Pd
What is the formula for the mean blood pressure?
- Pa= Pd + .33(Ps-Pd)
- Pa is the average pressure during a complete cardiac cycle
What is meant by laminar flow?
NO sounds
What are Korotkoff sounds?
sounds produced when an artery is partially constricted and blood flow becomes turbulentcausing the artery to vibrate
What is the oscillometry method?
turbulent blood flow occurs when the cuff pressure is greater than the diastolic and less than the systolic
Pd < tuburlance < Ps
How is the ausculation method used to measure blood pressure?
- 1st sound = systolic pressure
- 2nd sound= diastolic pressure
What are the physiologic factors that determin artieral blood pressure?
cardiac output and peripheral resistance
What is cardiac output in arterial blood pressure?
volume of blood being pumped out by the heart
heart rate * stroke volume
What are the phyhsical factors that determine arterial pressure?
arterial blood volume and arterial compliances
If stroke volume increases, what are the effects on arterial blood pressure?
- within the first cycle, diastolic pressure will remain the same
- every cycle after, diastolic pressure will increase causing the pulse pressure to increase
If stroke volume decreases, what are the effects on arterial blood pressure?
- within the first cycle, diastolic pressure will remain the same
- every cycle after, diastolic pressure will decrease causing the pulse pressure to decrease
If heart rate increases, what are the effects on arterial blood pressure?
- both diastolic and systolic increase
- pulse pressure has no change b/c there is no change to stroke volume
If heart rate decreases, what are the effects on arterial blood pressure?
- both diastolic and systolic decrease
- pulse pressure has no change b/c there is no change to stroke volume
If peripheral resistance decreases, what are the effects on arterial blood pressure?
- both diastolic and systolic decrease
- pulse pressure has no change
If peripheral resistance increases, what are the effects on arterial blood pressure?
- both diastolic and systolic increase
- pulse pressure has no change
What is resistance determined by?
blood viscosity, vessel length, vessel radius
length and viscosity considered constant
How is resistance reduced?
by an increase in radius
Vessel resistance is sensitive to what?
diameter and blood flow
What vessels have the lowest cross-sectional area (highest resistance)
aortas and large arteries
From arteries to arterioles, how is cross-sectional area and resistance blood pressure affected?
cross-sectional area is increased by decreasing resistance
What is vascular tone?
degree of constriction relative to its maximally dilated state
When do all arterial and venous vessels exhibit some degree of smooth muscle contraction?
under basal conditions
How do extrinsic factors regulate blood pressure?
by altering systemic vascular resistance
How is vascular tone determined?
by balance of competing vasocinstrictor and vasodilator influences
What are intrinsic vascular tones?
- tissue metabolites
- local hormones
- myogenic -> response to “snap back”
- endothelial factors
What is vascular stenosis?
abnormal narrowing of an artery
decreasing vessel diameter
What causes vascular stenosis?
atherosclerosis
Focal vacospasm can cause what?
acute stenosis
What is critical stenosis?
critical narrowing of an artery that results in reduction in maximal flow capacity
What is an example of critical stenosis?
narrowing of an iliac artery decreases flow to piriformis muscle
What is meant by blood vessel compliance?
ability of a vessel to distend and increase volume
What is the difference between stressed and unstressed volume ?
- stressed volume: that stretched the walls
- unstressed volume: the rest
What is blood volume compliance quantified as?
change in volume (V) / change in pressure (P)
What is the formula for arterial compliance?
Ca = change in Va / change in Pa
Va = arterial volume; Pa= arterial pressure
What is the formula for arterial elastance?
Ea = change in Pa / change in Va
What is the trend of elastance and compliance between arteries and veins?
- artery: increase elastance, decrease complaince
- vein: decrease elastance, increase compliance
Why is the compliance of arteries much lower than veins?
due to higher elastin and vascular smooth muscle
What is the trend between elastin and compliance?
as elastin decreases, compliance increases
What is the result of small changes in pressure?
increase in volume chages and compliance
What is the action of aortas and large arteries during systole and diastole?
- systole: distend
- diastend: recoil
How do arteries act as a pressure resevoir?
- allows continuous blood flow
- reduces workload on heart because recoil pushes remainder of blood to capillaries
- reduce blood pressure fluctuation
What is the effect of age on compliance?
compliance decreases with age
What is the effect of age on systolic and blood pressure?
they both increase with age
What are the causes of arterial stiffness?
- increase in collagen
- decrease in elastin
- decrease in expansion ability
What are the physical properties of veins?
- high compliance
- low resistance because pressure decreases to get blood back to heart
- blood reservoir system
- venous valves provide one way to flow towards the right heart
What are the biggest determinants of venous return ot the heart?
- pressure gradient
- skeletal muscle pump with venous valves
What is a skeletal muscle pump?
major mechanism promoting venous return during normal locomotory activity
Do veins in large muscles compress or decompress during muscle muscle relaxation/contraction?
- compress during contraction
- decompress during relaxation
What happens to the respiratory pump during inhalation?
- thoracic cavity expands
- pressure in pleural cavities drops
- pulls air into lungs
- blood pulled into the IVC and right atrium from smaller veins
What happens to the respiratory pump during exhalation?
- pressure in pleural cavity drops
- pushes blood into right atrium
important during heavy exercise
What happens to the respiratory pump during relaxation?
- pressuredecreases
- increases blood flow into thoracic veins
- diaphragm relaxes
What happens to the respiratory pump during contraction?
- pressure decreases
- increased intrathoracic pressure
- diaphragm relaxes
What is the process of regulated sympathetic vasoconstriction?
increased sympathetic > vasoconstriction> increase venous pressure> increase venous return> increase EDV
How does the cardiac suction effect affect venous returns?
increases it
Pu;;ing an aorta causes what?
an increase in atrial volume
decreasae in atrial pressure drives blood into aorta
