Hemodynamics

Question 1

hemodynamics

Answer 1

blood movement; the study of blood flow in the circulation

Question 2

what kind of reservoir are systemic veins

Answer 2

volume reservoir

high compliance to expand and contract to meet demands

contraction of veins pushes blood towards heart –> increases venous return

Question 3

what kind of reservoir are systemic arteries

Answer 3

pressure reservoir

low compliance –> greatest point of flow

Question 4

what type of vessels are the major regulator of vascular resistance

Answer 4

arterioles

Question 5

what is blood flow

Answer 5

the displacement of volume of blood per unit time

Question 6

what does it mean that blood flow is parabolic

Answer 6

fluid molecules on the outside move slower than those on the inside

outside molecules have friction with the vessels wall (slow)

inside molecules “slip” against the other fluid layers (fast)

Question 7

ohm’s law

Answer 7

pressure gradient = blood flow x resistance

deltaP = Q x R

Question 8

what are the two factors affecting blood flow (according to ohm’s law)

Answer 8

pressure difference and vascular resistance

Question 9

pressure difference & blood flow relationship

Answer 9

increase deltaP = increase blood flow

blood flows from high to low pressure –> greater pressure difference = stronger gradient –> faster flow

Question 10

can you change the pressure gradient in order to alter blood flow

Answer 10

NO - pressure gradients stay constant at a particular location

Question 11

what can you change to alter blood flow

Answer 11

resistance

Question 12

vascular resistance

Answer 12

friction of blood as it passes along the endothelium

Question 13

how does resistance affect flow

Answer 13

increase R = decrease flow

Question 14

poiseuille’s law

Answer 14

predicts blood flow based on the radius of the vessel

Q = (deltaP x pi x r^4) / (8 x n x L)

Question 15

how does radius affect flow

Answer 15

increase radius (vasodilation) = decrease resistance = increase flow

decrease radius (vasoconstriction) = increase resistance = decrease flow

Question 16

viscosity

Answer 16

“slipperiness” of blood vessels

lower viscosity = more slippery = sharper parabola (faster central flow)

Question 17

how does viscosity affect flow

Answer 17

increase viscosity = decrease flow

decrease viscosity = increase flow

Question 18

how does length of the vessel affect flow

Answer 18

blood flow slows along the length of the vessel due to friction

increase length = decrease flow

decrease length = increase flow

Question 19

Reynold’s number

Answer 19

measures the point at which blood flow increases beyond laminar flow and becomes turbulent (critical velocity)

Question 20

critical velocity

Answer 20

the speed at which blood flow transitions from laminar to turbulent

Question 21

aortic pressure

Answer 21

the potential energy available to move blood

Question 22

how does aortic pressure change across arteries

Answer 22

minimal change from aorta –> arteries

increase pressure from arteries –> arterioles (high resistance vessels)

Question 23

mean arterial pressure

Answer 23

average pressure in the arteries during the cardiac cycle

Question 24

MAP equations

Answer 24

MAP - CVP = CO x SVR
(CVP is negligible)

MAP = CO x SVR
MAP = (SBP + 2xDBP) / 3

Question 25

modified Bernoulli's equation

Answer 25

estimates pressure gradients using velocity of blood across a narrowed region deltaP = 4 x V^2

Question 26

how does velocity affect pressure gradient

Answer 26

narrow vessels = increased velocity = increased pressure difference wide vessels = decreased velocity = decreased pressure difference

Question 27

how does Bernoulli's equation apply to stenotic valves

Answer 27

aortic stenosis --> left ventricular pressure becomes significantly INCREASED compared to the pressure within the aorta (on other side of stenotic valve) --> increased velocity --> increased pressure gradient

Question 28

windkessel effect

Answer 28

recoil of the aortic wall during diastole to release blood that was stored during diastole allows perfusion to maintain throughout diastole

Question 29

pulse pressure

Answer 29

palpable pulse; the difference between systolic and diastolic blood pressure

Question 30

hyperdynamic pulses

Answer 30

bounding occurs with increased difference between systolic and diastolic BP (increased systolic or decreased diastolic or both) ex. aortic regurgitation

Question 31

hypodynamic pulses

Answer 31

weak/thready occurs when decreased difference between systolic and diastolic BP (decreased systolic or increased diastolic or both) ex. aortic stenosis

Question 32

what is pulse pressure influenced by

Answer 32

heart rate and stroke volume

Question 33

perfusion pressure

Answer 33

blood flow directed to perfuse organs ALL organs receive the same perfusion pressure

Question 34

how do organs alter local blood flow based on needs (since perfusion pressure is the same to all organs)

Answer 34

changing local arteriole diameter allows organs to maintain steady blood flow despite changes in systemic BP

Question 35

auto regulation of local blood flow

Answer 35

local response to changes in systemic perfusion pressure by changing local vascular resistance occurs within a range of systemic BPs

Question 36

systemic vascular resistance (SVR)

Answer 36

total peripheral resistance; the net resistance of entire systemic circulation

Question 37

what are surrogate measures of SVR

Answer 37

blood pressure/MAP

Question 38

vessels arranged in series

Answer 38

vessels arranged one after the other total resistance = R(1) + R(2) + ... etc

Question 39

vessels arranged in parallel

Answer 39

vessels arranged as parallel branches 1/total resistance - 1/R1 + 1/R2 + ... etc

Question 40

which vessel arrangement reduces total resistance

Answer 40

parallel

Question 41

how does resistance change as blood moves from arteriole to capillary

Answer 41

small radius so you would EXPECT resistance to increase as blood moves from arteriole --> capillary BUT capillaries are arranged in parallel so resistance decreases from arteriole --> capillary

Question 42

arteriole function

Answer 42

gate keepers - largely control flow to specific tissues by changing vascular resistance

Question 43

pulmonary vascular resistance

Answer 43

1/10 systemic vascular resistance able to accommodate increases in flow from increased CO to lungs and pressure by recruitment and distention of capillaries

Question 44

capillary recruitment

Answer 44

opening of additional capillaries to accommodate increased flow

Question 45

capillary distension

Answer 45

widening of capillary walls to accommodate increased flow