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100 Physical Prin of Medicine 1 Fall 2013 > CVT 100 #6 Physics PP Velocity > Flashcards

CVT 100 #6 Physics PP Velocity Flashcards

1
Q

Velocity for physicists, strictly speaking, involves both speed and direction. For us regular people:

A

just speed.

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2
Q

Velocity (speed):

A

distance over time e.g., miles per hour

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3
Q

UNITS

SI

A

m/sec

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4
Q

UNITS

CGS

A

cm/sec

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5
Q

UNITS

British

A

feet/sec

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6
Q

Common conversions:
m/sec to cm/sec
cm/sec to m/sec
move two decimal places

A

1.00 m/sec = 100 cm/sec

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7
Q

Velocity is influenced by

A

volume flow rate and cross-sectional area

Q and A

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8
Q

Flow cm3/sec
————– ———-
volume Area cm2

cancel cm2 to leave: cm/sec

A

—
V = Q
—
A

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9
Q

Note that this is MEAN velocity.

A

We will assume mean rather than peak velocity through this section.

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10
Q

If area decreases, what happens to velocity?

A

It goes up.

The kinked garden hose, the carotid stenosis, etc.

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11
Q

If area is cut in half (x 1⁄2), what happens to velocity?

A

If area is doubled, what happens to velocity?

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12
Q

How is the diameter of the Aorta?

A

~2.5 cm diameter

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13
Q

Aorta is ~2.5 cm diameter
What is area?
Two ways to get it:

A
  1. A = πr2
  2. A = D2 x .785 (Mayo clinic)

(2.5)2 x .785
= 4.9cm ^2 Area of aorta

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14
Q

If C.O. is 4.5 L/min, what is velocity?

A 
First convert L/min to cm3/sec
 4.5 L/min x 1000 mL/L 
                    ---------------
                     60 sec/min
 = 75 cm3/sec
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15
Q

If velocity of blood flow in the common carotid artery is 70 cm/sec, and flow through the artery is 3.6 L/min, then what is the CCA diameter?

A 
A = Q/V 
First change L/min to cm3/sec 
3.6 x 1000/60 = 
60 cm3/sec 
--------------
70 cm/sec
 Area = .86 2 cm
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16
Q 
How to get diameter from area: 
A = πr2, so r2 = A
                         ---
                          π
r2 = .86/3.14 = .27 cm
A

r2 = .86/3.14 = .27 cm
Square root of .27 is
.52 cm radius
2 x radius = diameter = 1.04 cm

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17
Q

What is diameter of aorta if
CO = 5 L/min
Velocity = 35 cm/sec?

A

Convert L/min
Calculate area
Calculate diameter

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18
Q

What is CO in L/min if
velocity = 45 cm/sec
diameter = 2.0 cm?

A

First get area
Then calculate
Then convert to L/min

19
Q

In the body, arteries branch repeatedly, so the total cross-sectional area becomes

A

progressively larger.

20
Q 
Blood moving from one vessel 
4 cm2 area to 
6 vessels 
2 cm^2 x 6 = 
12 cm^2
 total cross-sectional area
A

a

21
Q

What happens to velocity?

Flow is 75 cm^3/sec so velocity is______cm/sec in the single large parent artery.

A

For velocity in the branches, you must use the TOTAL CSA:

12cm^2

22
Q 
Formula for velocity: 
V = Q/A 
(Flow is the same as in the big parent artery.) 
V = 75 cm3/sec = 6.25 cm/sec 12 cm2 
—slower, because there’s more area.
A

a

23
Q

Aorta’s Diameter and Area

A

Diameter: 25 mm
Area: 4.9 cm2

24
Q

Capillaries Diameter and area

A

Diameter: .008 mm

Total area: 4500 cm2

25
Q

We already found velocity for 2.5 cm (diameter) aorta (with 4.5 L/min flow): 15.3 cm/sec
How about the capillaries given the same flow?

A 
V = Q/A 
= 75 cm3/sec
----------------
4500 cm2
= .017 cm/sec 
Compared to 15.3 cm/sec
26
Q

How about with scientific notation?
V = 7.5 x 10^1 cm^3/sec
————————-
4.5 x 10^3 cm2

A

= 1.7 x 10^-2 cm/sec

compared to 1.53 x 10^1 cm/sec

27
Q

Bifurcation:

A

dividing into two branches (Latin: “two-forked”)

28
Q

two factors that help to maintain constant flow through the body:

A
  1. Pressure drops

2. Parallel branching of vessels

29
Q

Problem: If C.O. is 5.5 L/min,
and aorta is 2.3 cm^2
what is the velocity of blood flow in the aorta?

A

a

30
Q

Problem: If C.O. = 5 L/min, and diameter of each of the three great vessels off the aortic arch is .8 cm, what is the velocity in the left subclavian artery?

A

a

31
Q

Convert L/min to cm3/sec
Divide flow by 3 branches
(This only works if the branches are equal.)

A

a

32
Q

Divide flow by 3 branches
(This only works if the branches are equal.)
Find area of one branch Calculate velocity in that branch
OR: Just use total area of the three branches and total flow…

A

a

33
Q

If the velocity in the arterioles is .20 cm/sec, and the total CSA of the 2,arterioles is 1000 cm what is the volume flow rate through the arterioles?

A

a

34
Q

If the velocity of blood flow in the CCA is 55 cm/sec, and flow through the artery is 1 L/min, what is the diameter of the CCA?

A

Convert the flow from L/min
Calculate area (A = Q/V)
Divide by pi, then get square root for the radius Double it for diameter

35
Q

What’s the deal with area vs. diameter?

A

It’s all about angiography…

Area is a better indicator of true effect of stenosis, but diameter is what we get with angio.

36
Q

Next concept: The continuity equation

A

—

Q = V x A

37
Q

If the system is closed, then flow is

A

the same at all levels.

38
Q

If flow is the same in both places, then what is the relationship between velocity and area in both places?

A

Q1 = Q2
Q = V x A
so V1 x A1 = V2 x A2

39
Q

You can rearrange to solve for one of the areas:
A1 = A2 x V2
———-
V1
This is used in echocardiography to solve for valve areas.

A

a

40
Q

Velocity in LVOT is 100 cm/sec
Area of LVOT is 10.2 cm2
Velocity just beyond aortic valve is 450 cm/sec What is aortic valve area?

A 
A1 = A2 x V2 
        ----------
             V1 
=10.2 cm^2 x 100 cm/sec 
-------------------------------
               450 cm/sec 
= 2.27 cm2
41
Q 
Be sure to convert to and calculate with 
cm 
so that answer will be in 
cm2. 
And find area if you’re given diameter.
A

a

42
Q

How do we get diameter/area?

A

Ultrasound image.

43
Q

How do we get velocity readings?

A

Doppler ultrasound— frequency shift due to motion.

44
Q

What is the velocity at a stenotic site in the superficial femoral artery if:
Velocity proximal to stenosis is 60 cm/sec Diameter of artery proximal to stenosis is 4 mm Diameter of artery at the stenosis is 2.6 mm

A

a

100 Physical Prin of Medicine 1 Fall 2013 (9 decks)

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