Hemodynamics

Question 1

Where is the blood volume in the body?

Answer 1

Question 2

transmural pressure

Answer 2

pressure difference between the outside and inside of athe vessel wall

Question 3

hydrostatic pressure

Answer 3

pressure difference between one height and another in the body

no matter the position of the body, the pressure differential from artery to vein is equivalent in each region

Question 4

pressure gradient

Answer 4

the pressure difference between two locations

in normal circulation, pressure favors going back to the heart

may be reversed in the capillaries

Question 5

components that determine flow

Answer 5

driving pressure, resistance, and hydrostatic influences

Question 6

relationship between velocity and vascular cross secional area

Answer 6

flow = (cross-sectional area) x (blood velocity)

Q = A x V

Question 7

Poiseuille’s Law

Answer 7

Q = [(P₁-P₂)*pi*r⁴]/(8*eta*L)

P = pressure

r = radius

L = length

eta = viscosity

Q = flow

R = resistance

Question 8

Bernoulli Principle

Answer 8

total fluid energy (pressure) in flowing blood: E_total = E_potential + E_kinetic + E_gravity

E_potential: potential energy from cardiac contractionl stored in vessel walls

E_kinetic: kinetic energy in direction of blood flow; increases in proportion to blood velocity

E_gravity: gravity can increase or decrease pressure depending on position relative to heart

Question 9

What is viscosity of blood dependent on?

Answer 9

fibrinogen concentration

hematocrit

vessel radius

linear velocity

temperature

Question 10

shear stress

Answer 10

resistance to movement between laminae (pressure)

Question 11

sheer rate

Answer 11

relative velocities between laminate (velocity of blood flow)

Question 12

viscosity

Answer 12

shear stress/shear rate

(pressure/velocity)

unit = Poise (dyne sec/cm.sq.)

Question 13

laminar flow

Answer 13

flow in blood vessels occurs in longitudinal, concentric layers

central layers move faster than those near the vessel wall (parabolic velocity profile)

fluid elements remain in a given layer as they move along

Question 14

viscosity, hematocrit, and blood velocity

Answer 14

apparent viscocity of blood dcreases as the shear rate or velocity increases

the higher the hematocrit, the higher the viscosity

“shear thinning”

Question 15

turbulent flow

Answer 15

irregular flow with lateral components producing eddies and vortices - dissapates energy, may be accompanied by audible vibrations (murmurs or bruits)

predisposing factors for turbulence - sharp bends or obstructions

Question 16

viscosity effect of vessel size

Answer 16

blood viscosity is relatively insensitive to changes in vessel radius for large vessels

but decreases steeply with decreases in radius for smaller vessels

Question 17

Reynold’s number

Answer 17

index for turbulence

dimensionless number indicating propensity for turbulent blood flow

the higher the Reynold’s number (>3000), the greater the chance for turbulent blood flow to develop

N_R = (rho*D*v)/(eta)

D = vessel diameter

v = blood velocity

eta = blood viscosity

rho = blood density

Question 18

axial streaming

Answer 18

high velocity flow causes red cells to move toward the center of the stream leaving “plasma rich-RBC poor” fluid near the vessel wall

Question 19

plasma skimming

Answer 19

refers to the tendency of branching blood vessels to have relatively less RBCs

problem is solved by arterial cushions that slow down and push them into the branching vessels

Question 20

pressures in the systemic circulation

Answer 20

resistance is found precapillary

from the veins back toward the right heart, there is an even smaller pressure gradient and lower resistance

Question 21

where does the largest pressure drop occur?

Answer 21

arterioles

arteriolar constriction increases pressure in the proximal arterial system and increases the pressure drop

arteriolar dilation decreases proximal arterial pressure and decreases the pressure drop

Question 22

CV Pressure-Flow/Resistance relationships

Answer 22

in the CV system, there is no flow at a positive driving pressure, this varies with activation of the sympathetic nervous system

sympathetic activation (constriction) alters the pressure-resistance relationship

Question 23

critical closing pressure

Answer 23

the amount of pressure necessary just before flow is seen in a vessel