Block 3 - Bsf: Hemodynamics

Front 1

Define flow (often called volume flow).

Back 1

Amount of volume moved through a tube per unit time.

Front 2

What is the equation for flow?

Back 2

Q = A* (change in x/ change in t)

Front 3

What is the relationship between velocity of flow and cross-sectional area?

Back 3

The velocity of flow depends on cross-sectional area
v = Q/A
Q = A*v

Front 4

T/F

Total volume flow can vary between levels of arborization.

Back 4

False!

Since F = v*A +v*A + v*A….total volume flow must be the same at any level of arborization.

Front 5

Blood leaving the aorta has a (smaller/greater) velocity than blood traveling through a capillary.

Why?

Back 5

Greater

Although capillaries are small, the total CSA across the capillary bed is much larger than the aorta so velocity, and hence flow is slower than in the aorta.

Front 6

Velocity is maximal in the aorta at a)_________ and decreases during b)_________.

Back 6

a) Systole
b) Diastole

Front 7

T/F

Heart imparts pressure in a pulsatile manner.

Back 7

True!

Front 8

a) Between velocity and pressure, which is equal to kinetic energy?

b) Which is equal to potential energy?

Back 8

a) Velocity
b) Pressure

Front 9

What is the equation for total pressure (based on different types of pressure)?

Back 9

Ptotal = Plat+ Pdyn

Plat is lateral pressure
Pdyn is dynamic pressure
Pdyn = (ρv^2)/2

Front 10

Describe Bernoulli effect.

Back 10

For horizontal fluid flow, an increase in the velocity of flow will result in a decrease in the lateral pressure.

Front 11

Why is the trade-off between velocity and pressure important?

Back 11

Reduction of lateral pressure can affect filling of vessels.

Front 12

Where are the orifice of the right and left coronary arteries located?

Back 12

In aortic sinuses of the ascending aorta, just behind the leaflets of the valves and perpendicular to the flow of blood.

Front 13

In aortic stenosis, what happens to velocity of flow, PE/KE, and lateral pressure?

Back 13

Velocity of flow increases resulting in a conversion of potential energy into kinetic energy resulting in a fall in lateral pressure.

This reduces the filling pressure of the coronary vessels.

Front 14

How are flow and pressure related?

Back 14

Flow is directly proportional to ∆P.

Front 15

∆P must be expressed in relationship to:

Back 15

some reference pressure (P1)

Front 16

What types of pressure do you need to consider when thinking of blood flow?

Back 16

Driving pressure
Hydrostatic pressure

Front 17

Pressure difference between 2 points, A1 and A2, along
the axis of a tube (vessel) is the what?

Back 17

Driving pressure

Front 18

Pressure is the same everywhere if the tube/vessel is:

Back 18

Horizontal

Front 19

Pressure increases at the bottom if the tube/vessel is:

Back 19

Upright, because of gravity

Front 20

Because the pressure at the bottom of a tube/vessel is greater than the top, this also increases what at the bottom?

This results in greater _________________________.

Back 20

Transmural pressure

Hydrostatic pressure force

Front 21

Define pressure.

Back 21

Pressure is the height blood can drive a column of liquid either mercury (mmHg) or water (cmH2O)

Front 22

What is the equation for pressure?

Back 22

P = ρgh
ρ = density of liquid; g = gravitational constant; h = height of column

Front 23

What is a sphygmomanometer?

Back 23

A blood pressure gauge

Front 24

What equation can be used to understand steady flow of blood driven by a constant pressure head?

Back 24

Ohm's law:

F = dP/ R
dP = F * R
R = dP/F

Where:
dP = pressure difference (mmHg)
between upstream (P1) and downstream (P2)
F = flow (ml/min)
R = resistance

Front 25

Flow between two columns connected by a tube at their bottoms is proportional to what?

Back 25

The difference between the pressures of the 2 columns.

Front 26

T/F

There is a small pressure gradient in the cardiovascular circuit.

Back 26

False!

There is a large pressure gradient in the cardiovascular circuit

Front 27

How do you calculate the pressure gradient in the cardiovascular circuit?

Back 27

P = LV - RA

120-2 = 118

Front 28

F(Q) = total mean flow in the circulation = HR x SV = ???

Back 28

Cardiac Output (CO) in liters/min

Front 29

Flow is (directly/inversely) proportional to resistance.

Back 29

Inversely

F = dP/R

Front 30

The factors influencing resistant to flow in a straight, rigid, cylindrical tube are described by what equation?

Back 30

Poiseuille’s equation

(8nl)/(π*r^4)

r = radius
n = viscosity
l = length

Front 31

What are the 3 factors that alter resistance?

Back 31

Radius, viscosity, and length

Front 32

What can the radius in a vessel be changed by?

Back 32

Factors that influence vascular diameter such as vasoconstriction and/or dilation.

Front 33

What is the most impacting factor in resistance?

Back 33

Radius

Doubling the radius decreases resistance by a factor of 16! (and increases flow)

Front 34

What can the viscosity in a vessel be altered by?

Back 34

By changing hematocrit which changes the thickness of blood.

Front 35

What can alter length of a vessel?

Back 35

Length is not usually altered physiologically so it remains constant.

Front 36

What are the 6 assumptions of Poiseulle's relation?

Back 36

1) flow must be laminar
2) velocity of thin fluid layer at wall is zero
3) tube is straight, rigid cylinder w/constant radius
4) fluid is incompressible
5) viscosity of fluid must be constant
6) flow must be steady

Front 37

Describe laminar flow or “viscous” flow.

Back 37

Fluid moves in a series of layers with each stratum moving at a different velocity from the neighboring layer. In a tube, fluid along the wall is motionless and fluid in the center has maximal velocity.

Front 38

What is the ratio of shear stress, τ, to shear rate, du/dy?

Back 38

Viscosity

Front 39

The “thicker” the fluid the (lesser/greater) force that needs to be applied to move the plate on the surface.

Back 39

Greater

Front 40

In general, in any flow, layers move at a)(the same/different) velocities and the fluid's b)___________ arises from the shear stress between the layers that ultimately opposes any applied force.

Back 40

a) Different
b) Viscosity

Front 41

What is the term for the volume of whole blood that is cells, mostly red blood cells?

Back 41

Hematocrit

Front 42

Which condition has decreased RBC's and viscosity?

Back 42

Anemia

Front 43

Which condition has increased RBC's and viscosity?

Back 43

Polycythemia

Front 44

What is the equation for total peripheral resistance?

Back 44

R total = dP (change in pressure)/ F (cardiac output)

where dP is change in pressure across entire circulation (Paorta – Pveins)

Front 45

The total resistance (Rt) equals the sum of the individual resistances when resistances are arranged in:

Back 45

Series

Front 46

The total resistance (Rt) equals the sum of the reciprocal of individual resistances when resistances are arranged in:

Back 46

Parallel

Front 47

Total resistance is less than any individual resistance when resistances are arranged in:

Back 47

Parallel

Front 48

What is it called when blood flows smoothly along the tubes with fastest flow in the center of the vessel?

Back 48

Laminar flow

Front 49

What is it called when flow is not smooth but random with loss of kinetic energy?

Back 49

Turbulent flow

Front 50

What are the ranges for laminar to turbulent flow in regards to Reynold's number?

Back 50

Re < 2000 laminar
Re 2000-3000 some turbulence
Re > 3000 turbulent

Front 51

In regards to Reynold's number, a larger velocity results in what?

Back 51

Greater chance for turbulence

Front 52

In regards to Reynold's number, a larger diameter vessel (such as aorta) results in what?

Back 52

Greater chance of turbulent flow, because there's more area available for flow.

Front 53

In regards to Reynold's number, higher viscosity results in what?

Back 53

Less chance of turbulent flow, because the blood moves slower.

Front 54

In regards to Reynold's number, higher density blood results in what?

Back 54

Greater chance for turbulent flow

Front 55

What can produce audible vibrations often heard as murmurs?

Back 55

Turbulence

Front 56

In what 2 ways can murmurs due to turbulence occur in anemia?

Back 56

Anemia reduces viscosity (increased reynold's number)

High flow velocities because of increased cardiac output in anemia (increased reynold's number)

Front 57

When do changes in cross-sectional area contribute to murmurs from turbulence?

Back 57

Just after a branch point
Blood passing through a narrowed cardiac valve
Blood passing through an abnormal widening such as an aneurysm

Front 58

What are more likely to form in areas of turbulent flow?

Back 58

Thrombi (blood clots)

Front 59

What is the maximal pressure imparted by the heart?

Back 59

Systole ~ 120mmHg

Front 60

What is the minimal pressure imparted by the heart?

Back 60

Diastole ~ 80mmHg

Front 61

Pulse pressure is calculated by:

Back 61

Systole minus diastole

Front 62

In talking about flow, usually think in terms of what?

Back 62

Mean arterial pressure (MAP)

This is not the mean of systole and diastole, must take into account time spent in each part of cardiac cycle.

Mean pressure ~ 95mmHg

Front 63

What allows steady state flow in the heart?

Back 63

Aortic compliance

Front 64

Compliance decreases with age, causing what?

Back 64

Flow is less “steady” and pressure pulses are not dampened as easily.

Front 65

Decreased compliance is usually a manifestation of what?

Back 65

Increased vessel rigidity (arteriosclerosis).

Front 66

Does decreased compliance increase or decrease cardiac work?

Back 66

Decreased compliance increases cardiac work.