Arterial System

Question 1

What is hydraulic filtering?

Answer 1

The compressibility of air trapped converts intermittent inflow of water to a steady outflow of water

Question 2

What does the windkessel effect explain?

Answer 2

hypertension
it separates the conduit and cushioning function of the arterial tree
an increase in TPR + decrease in arteral compliance = hypertenison

Question 3

What occurs in the windkessel effect when only resistance increases?

Answer 3

MAP rises to an equal increment in systolic and diastolic pressures

Question 4

What occurs in the windkessel effect when resistance increases and compliance decreases?

Answer 4

MAP increases to the same extent as with only increased resistance
but pressure oscillations are increased resulting in disproportionate increase in systolic BP and little changes to diastolic

Question 5

What occurs during systole with compliant arteries?

Answer 5

a substantial fraction of SV is stored in the arteries, the arterial walls are stretched
*reservoir effect

Question 6

What occurs during diastole with compliant arteries?

Answer 6

previously stretches arteries recoil, the volume of blood displaced by recoil facilitates continuous capillary flow in diastole (secondary pump to maintain diastolic pressure)

Question 7

What occurs during systole with rigid arteries?

Answer 7

virtually none of the SV can be stored in the arteries (increased force to push SV, increased speed of flow)

Question 8

What occurs during diastole with rigid arteries?

Answer 8

arteries cannot recoil
increased *MVO2

Question 9

What is the duration of cardiac SV discharge during systole?

Answer 9

about 1/3 of a cardiac cycle

Question 10

When is most of the SV pumped?

Answer 10

during rapid ejection (about 1/2 of systole)

Question 11

How is part of the energy of cardiac contraction dissipated?

Answer 11

as forward capillary flow during systole
remaining energy in distensible arteries is stored as potential energy

Question 12

What does the elastic recoil of arterial walls convert potential energy into?

Answer 12

into capillary blood flow

Question 13

What occurs to capillary flow during diastole if arterial walls are rigid?

Answer 13

capillary flow would have ceased

Question 14

What effect does hydraulic filtering have on cardiac workload?

Answer 14

decreases MVO2
more work is required to pump a given flow intermittently than steadily
*The steadier the flow, the less the excess work

Question 15

At any given stroke volume, what is the relationship of MVO2 with rigid arteries?

Answer 15

A rigid artery will increase MVO2

Question 16

What is the equation for aortic compliance?

Answer 16

Dv/DP
change in volume/change in pressure

Question 17

What is the effect of age on aortic compliance?

Answer 17

For any pressure about 80 mmHg, the aortic compliance will decrease with age

Question 18

What causes the decrease in aortic compliance with age?

Answer 18

progressive changes in collagen and elastin contents of arterial walls (decrease)
decrease in diameter of the aorta during each cardiac contraction
*offset with exercise

Question 19

How does heart failure affect the relationship between age and aortic compliance?

Answer 19

reduction in aortic compliance with age is normal
heart failure (disease) + age = magnified decrease in compliance

Question 20

What are the two major limitations of the windkessel model?

Answer 20

1. the arterial tree doesn’t separate conduit and cushioning functions
2. it makes the assumption that PWV is of infinite value

Question 21

Explain the limitations of the windkessel model: the arterial tree doesn’t separate conduit and cushioning functions

Answer 21

both are features of the aorta and its major branches which are distensible tubes
there is a progressive loss of cushioning function, from the ascending aorta to more muscular and increasing conduit function of large arteries from heart to periphery

Question 22

Explain the limitations of the windkessel model: it makes the assumption that PWV is of infinite value

Answer 22

can’t be the case because of heterogeneity of PWV along the arterial tree
- determines by cushioning and conduit functions in adjacent arterial segments
peripheral arteries are stiffer than central, leading to an increase in amplitude of pressure wave in vessels from heart to periphery
the stiffness of medium-sized peripheral arteries is modulated by vasomotor tone (how constricted) either depending on the endothelial function or sympathetic NS or renin-angiotensin system

Question 23

What is the gold standard for measuring arterial stiffness?

Answer 23

PWV

Question 24

Why is a propagative model (like PWV) widely used?

Answer 24

assumes each pulse wave has a finite value
it clearly illustrates the facts that the propagation of the pulse wave is inversely related to compliance of the artery

Question 25

What will a faster PWV do to the compliance of a vessel?

Answer 25

decreases the compliance

Question 26

What is the equation for PWV?

Answer 26

PWV = Length/change in time

Question 27

How is a tonometer used to measure PWV?

Answer 27

used at different sites difference in the onset of the wave forms with one heart contraction

Question 28

What does less time between the onset of wave forms with a tonometer indicate?

Answer 28

a faster PWV

Question 29

Is a faster or slower PWV better?

Answer 29

slower with compliance energy will be absorbed by walls without compliance energy is forced forward = increased velocity * PWV is an indication of compliance

Question 30

What is an arterial pressure waveform made up of?

Answer 30

forward pressure wave exerted by ventricular contraction + reflected wave

Question 31

Where are waves mainly reflected from in the periphery?

Answer 31

branch points or sites of impedance mismatch (sudden narrowing)

Question 32

What is the effect of reflected waves in elastic vessels?

Answer 32

because PWV is low they tend to arrive back at aortic root during diastole

Question 33

What is the effect of reflected waves in stiff vessels?

Answer 33

PWV rises and the reflected wave arrives back at the central arteries earlier (during systole), adding to the forward wave and augmenting the systolic pressure

Question 34

What is the augmentation index (Alx)?

Answer 34

difference between the second and first systolic peaks expressed as a percentage change of pulse pressure = peak of reflected wave / peak of ejection wave

Question 35

What physical factors can play an important role in wave reflection?

Answer 35

geometry number of arterioles architecture of microvascular network

Question 36

What does arterial and arteriolar constriction result in regarding reflected waves?

Answer 36

reflection points closer to the heart, leading to earlier aortic wave reflections *increased augmentation

Question 37

What does increased aortic stiffness cause regarding reflection waves?

Answer 37

waves to travel more rapidly and arrive earlier in systole superimposing on the forward wave and boosting systolic pressure

Question 38

What is the primary source of stiffness?

Answer 38

aorta

Question 39

What physiological factors affect arterial blood pressure?

Answer 39

CO (HR x SV) peripheral resistance

Question 40

What physical factors affect arterial blood pressure?

Answer 40

arterial blood volume arterial compliance

Question 41

What is pulse pressure?

Answer 41

systolic - diastolic a function of SV and arterial compliance

Question 42

During rapid ejection what occurs to blood volume? *compliance is held constant

Answer 42

the volume of blood introduced into the arterial system exceeds the volume that exits - arterial pressure and volume will increase

Question 43

When is maximum arterial blood volume reached?

Answer 43

at the end of rapid ejection, corresponds to peak pressure (systolic pressure)

Question 44

What does pulse pressure correspond to?

Answer 44

some arterial volume increment

Question 45

What does the volume increment equal?

Answer 45

volume of blood discharged by LV during rapid ejection minus volumes that that run off to the periphery during same phase of cardiac cycle *~80% of SV raises arterial volume rapidly

Question 46

What occurs to the pressures and volume increment during diastole?

Answer 46

volume and pressure will fall * peripheral runoff will exceed cardiac ejection

Question 47

If SV is suddenly doubled, what occurs to mean arterial pressure? *compliance is held constant

Answer 47

it will double arterial pressure will now oscillate with each heart beat about this new value of mean arterial pressure

Question 48

How would a normal heart eject the new greater SV? *compliance is held constant

Answer 48

during a fraction about equal to what prevailed at lower SV

Question 49

How would the greater volume increment be reflected in the pulse pressure? *compliance is held constant

Answer 49

pulse pressure would be twice as great (driven by volume)

Question 50

What occurs when both mean and pulse pressure increase? *compliance is held constant

Answer 50

the increase in systolic pressure exceeds the increase in diastolic pressure

Question 51

What is the effect of heart failure on pulse pressure and SV?

Answer 51

very small pulse pressure because SV is abnormally small

Question 52

What is the effect of a large SV on pulse pressure?

Answer 52

likely to have large pulse pressure

Question 53

What is a well-trained athlete's pulse pressure?

Answer 53

have low resting HR prolonged ventricular filling times induce the ventricles to pump a large quantity of blood per beat thus a large pulse pressure

Question 54

What is the effect of compliance on pulse pressure?

Answer 54

with the same volume increment, there will be greater pulse pressure in less compliant arteries * workload on LV will be greater even if SV, TPR, and arterial pressures are equal

Question 55

What does pulse pressure vary as a function of?

Answer 55

compliance