Hemodynamics

Question 1

flow of blood through arterial system

Answer 1

arteries -> arterioles -> capillaries

Question 2

flow of blood through venous system

Answer 2

capillaries -> venules -> veins

Question 3

function of pulmonary and aortic valves (semilunar)

Answer 3

prevent backflow of blood into ventricles

Question 4

function of tricuspid and mitral valves

Answer 4

prevent backflow of blood into atria

Question 5

distinguishing fibers between arteries and veins

Answer 5

• arteries: contain more smooth muscle and elastic fibers
• veins: contain more collagen fibers

Question 6

what is compliance

Answer 6

the ability of a cardiac chamber (or vessel) to change its volume (V) in response to changes in pressure (P)

C=change in volume / change in pressure

Question 7

which vessel has the higher compliance: arteries vs veins

Answer 7

• C of veins is highest: can store large amount of volume of blood in veins with relatively low pressure

*steeper the slope, the higher the compliance of the vessel

Question 8

define zero compliance

Answer 8

no change in volume in the presence of infinite changes in pressure

Question 9

define infinite compliance

Answer 9

even at zero pressure, the volume of a vessel is infinite

Question 10

define finite compliance

Answer 10

“real life”

• for a given change in pressure, there will be a change in volume

Question 11

describe the change in compliance that occurs with growing pressure and volume of vessels

Answer 11

• at low pressures and volumes, compliance is much greater than at high pressures and volumes
• the change in volume for a given change in pressure is greater at higher compliance

Question 12

what is the pressure gradient of the cardiovascular system

Answer 12

• difference in pressure at two or more points along the systemic circuit
• main driving force
• ventricular ejection provides the continuous pressure gradient, allowing blood to flow

Question 13

give the equation that gives the velocity of blood flow

Answer 13

v = Q/A

• v = velocity of blood flow (cm/sec)
• Q= flow (ml/sec)
• A= cross sectional area (cm2)
• A = πr²

Question 14

describe why velocity of blood flow through the capillaries is slow even though v=Q/A

Answer 14

• blood flow is identical throughout the vascular tree
• need to take into consideration the surface area of ALL of the capillaries (which is much larger than the aorta)
• velocity of flow is inversely proportional to the TOTAL cross sectional area

Question 15

what is the relationship between blood flow, pressure, and resistance

Answer 15

Flow (Q) = change in pressure / resistance

* change in pressure is the driving force and resistance is the impediment to flow

Question 16

what is vascular resistance

Answer 16

measure of hindrance to blood flow caused by friction between moving blood and the vessel wall

Question 17

what is Poiseuille’s equation: determines resistance

Answer 17

R = 8 n l / πr⁴

• R = resistance
• n = viscosity of blood
• L= length of blood vessel
• r= radius

* most important factor is radius

Question 18

what is the major determinant of flow rate

Answer 18

radius: R = 1/r⁴
* small radius confers more resistance because blood “rubs” against a larger surface area

Question 19

how do you determine resistance in a series

Answer 19

R total = R1 + R2 + R3 …

Question 20

how do you calculate resistance in parallel

Answer 20

1/R total = 1/R1 + 1/R2 + 1/R3

Question 21

with a series arrangement, total flow through each level equals what? What happens to the pressure as blood flows through each component?

Answer 21

• it is the same; output from the aorta = venous return
• pressure decreased as blood flows through each component

Rtotal = R artery + R arteriole + Rcapillary + Rvenule + Rvein

Question 22

the cardiac output is distributed in % among the organs. what equations show that

Answer 22

Qi = Q1 + Q2 + Q3

Qi / (Pi-Po) = Q1/ (Pi-Po) + Q2/ (Pi-Po) + Q3/ (Pi-Po)