12/2/2014 Medical Physiology Systemic Circulation Amit S. Dhamoon

Question 1

What does the concept of compliance refer to in general?

Answer 1

Compliance = V/P

• blood vessels have finite compliance

Question 2

In blood vessels, the greater the volume of fluid, the ___ the pressure

Answer 2

greater

Question 3

Define compliance (C) of an elastic vessel

Answer 3

Proportionality factor
that relates the change in volume, ∆V, to a change in transmural pressure, ∆P(tm)
∆V = C∆P(tm)
or
C = ∆V/∆PTM

Question 4

What is another name for compliance?

Answer 4

Capacitance (ml/mm Hg)

Question 5

Define transmural pressure

Answer 5

P(tm) –> difference in pressure between the inside and the outside of the vessel

Question 6

A rigid tube has a compliance of ___

Answer 6

zero

Question 7

Define elastance (E)

Answer 7

Inverse of compliance

E = ∆P(tm)/∆V

Question 8

Define distensibility (D) or specific compliance

Answer 8

Fractional change in volume for a given change in pressure

D = ∆V/V∆P(tm) = C/V.

Question 9

What determines vascular compliance?

Answer 9

The relative proportion and arrangement of smooth muscle, and elastin and collagen fibers in the vessel wall

Question 10

Describe the function of each type of vessel

Answer 10

1) aorta
- conduit of blood from the heart
- high pressure vessel.

2) arterioles
- resistance vessels
- regulate blood flow through individual organs
- affected by sympathetic nervous system

3) capillaries
- exchange vessels

4) veins
- capacitance vessels
- contain >50% of blood volume

Question 11

Because blood vessels are ___, they can expand and contract depending upon the pressure, changing blood volume contained within

Answer 11

distensible

Question 12

Compliance is the medically important measure of how the distensible ___ changes volume with pressure

Answer 12

blood vessel

Question 13

Vascular compliance is determined by arrangement of ___ and ___ and is not homeostatically regulated parameter like pressure

Answer 13

elastic fibers; smooth muscle

Question 14

Compliance is measured from the ___ of a Pressure-Volume curve

Answer 14

slope

Question 15

Another way to quantify the elastic properties of vessels is ___

Answer 15

distensibility

Question 16

Why do arteries function as resistance vessels?

Answer 16

They have low volume capacity, expand modestly and maintain resistance over wide pressure levels

Question 17

Why do veins function as volume reservoirs or capacitance vessels?

Answer 17

They expand greatly (also change shape) with small pressure changes due to the high compliance and have large volume changes

Question 18

With increasing age, vascular compliance ___ dramatically, and the heart must work
___ to pump blood through stiffer vessels

Answer 18

decreases; harder

Question 19

A given stroke volume would produce a ___ pulse pressure in older individuals than in younger ones

Answer 19

greater

Question 20

With increasing age the Windkessel effect is ___, causing pulsatile flow to persist in the capillaries

Answer 20

decreased

Question 21

Regular exercise ___ cardiac contractility and stroke volume so that the heart may pump
blood through vessels that are stiffer and that may also have higher resistance due to ___

Answer 21

increases; atherosclerosis

Question 22

What is the Windkessel effect?

Answer 22

German for wind chamber –> the storage of blood during systole by the aorta, pulmonary artery and their major branches

Question 23

What is the consequence of the Windkessel effect?

Answer 23

The maintenance of blood flow during diastole

Question 24

For a given cardiac output, Q, the mean pressure decreases with increasing distance from the heart in accordance with Poiseuille’s law:

Answer 24

P2 = P1 - (8ηQ/πr4)L

Question 25

The greatest pulse pressure is in the ___

Answer 25

left ventricle

Question 26

Why does blood flow?

Answer 26

Because cardiac contractions create pressure in the fluid contained within the heart, thus establishing a pressure gradient of about 100 mm Hg between the aorta and the vena cava

Question 27

Is the pressure on the arterial side pulsatile in the systemic circulation?

Answer 27

Yes

Question 28

What facilitates the damping of the pressure oscillations and the steadiness of the blood pressure as the large resistance of the smaller arterioles is encountered?

Answer 28

The Windkessel effect

Question 29

Why is pulmonary resistance less than systemic resistance?

Answer 29

Because in the pulmonary capillaries the pressure remains pulsatile, oscillating between lower limits than in the systemic circulation

Question 30

The arterial pulse contour shows the time course of the ___ in the arteries of the systemic circulation during a single cardiac cycle

Answer 30

transmural pressure

Question 31

As the heart beats, a continuous sequence of ___ pressure waves is generated at a frequency of 1-2 Hz (hertz, cycles per second)

Answer 31

pulsatile

Question 32

Define systolic pressure, Ps

Answer 32

Maximum pressure reached by the arterial pressure as blood is ejected from the heart during systole

Question 33

Define diastolic pressure, Pd

Answer 33

Minimum pressure reached by the arterial pressure as the heart relaxes and refills during diastole

Question 34

The mean arterial pressure is equal to the steady pressure required to maintain the ___ through the total peripheral resistance

Answer 34

cardiac output

Question 35

What does the shape of arterial pulse contour reflect?

Answer 35

Events of cardiac cycle and elastic properties of the vessels

Question 36

What is the anacrotic limb?

Answer 36

Rising part of aortic pressure wave

Question 37

What causes the anacrotic limb?

Answer 37

Blood entering aorta from left ventricle during systolic ejection

Question 38

What is peripheral runoff?

Answer 38

Flow of blood from arteries into capillaries

Question 39

What is the dicrotic notch or incisura?

Answer 39

Momentary reversal of blood flow, which closes the aortic valves and creates a transient increase in aortic pressure

Question 40

Pulse pressure is directly proportional to ___ and inversely proportional to ___

Answer 40

stroke volumen; compliance