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Heart Implants > TAH & LVAD > Flashcards

TAH & LVAD Flashcards

1
Q

What are the 7 important design issues?

A 
Anatomical fit
Physiological function
Blood compatibility
Tissue compatibility
Bench top testing
Animal testing
Human studies
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2
Q

What does BiVAD stand for?

A

Bi-ventricular assistive device

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3
Q

What does LVAD stand for?

A

Left ventricle assistive device

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4
Q

What are the two factors to consider when thinking about anatomical fit?

A

Placement

Connection to circulatory system

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5
Q

What are the two types of LVADs?

A

Pulsatile and non-pulsatile

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6
Q

Describe a BiVAD.

A

Bypasses both ventricles, i.e. blood goes from atria to aorta. Blood pump stays outside the body.

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7
Q

Describe an LVAD type 1.

A

Only left ventricle is bypassed (including valves).

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8
Q

Describe an LVAD type 2.

A

Bypasses valve between left ventricle and aorta. (Aortic valve).

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9
Q

Describe a TAH.

A
  1. Left and right failing ventricles are removed.
  2. Left and right atria, aorta and pulmonary artery remain intact.
  3. Quick connects are sewn in and the artificial heart is attached.
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10
Q

What type of pump is the left ventricle?

A

Pressure pump.

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11
Q

What type of pump is the right ventricle?

A

Volumetric pump.

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12
Q

Where is the blood pressure measured?

A

Aorta

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13
Q

What does SVR stand for?

A

Systemic vascular resistance

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14
Q

What does PVR stand for?

A

Pulmonary vascular resistance

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15
Q

What is the relationship between PVR and SVR?

A

PVR is 10x smaller.

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16
Q

Describe the difference between Novacor and Texas Heart LVADs.

A

Novacor - usually patient has some level of cardiac output, driven by a magnet.
Texas Heart - take blood from apex and pump into descending aorta, not used anymore due to signs of poor perfusion in upper body.

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17
Q

What is an advantage of non-pulsatile devices?

A

Membrane doesn’t have to move as you are continuously pushing blood through and not pumping back and forth.

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18
Q

Why are all external implants transparent?

A

To allow doc to see any protein layer build up in blood, which could travel to brain or aorta and cause death.

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19
Q

What are the six categories of physiological function?

A 
Full support (TAH, BiVAD, LVAD)
Partial support (LVAD)
Pulsatile or non-pulsatile
Short term (days, weeks)
Long term (months)
Permanent (doesn't exist)
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20
Q

What is the mean flow for both ‘circuits’?

A

3-5 L/min

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21
Q

What is the normal range for systemic arterial pressure?

A

90-140/60-90 mmHg

22
Q

What is the normal range for pulmonary arterial pressure?

A

15-39/8-14 mmHg

23
Q

What is the normal range for right atrial pressure?

A

0-7 mmHg

24
Q

What is the normal range for left atrial pressure?

A

4-12 mmHg

25
Q

What is the normal range for SVR?

A

24.6-29.8 Wood Units

26
Q

What is the normal range for PVR?

A

2.8-3.9 Wood Units

27
Q

What is the normal range for Cardiac Index?

A

2.5 - 4 L/min/m^2

28
Q

What is the diameter of the aorta?

A

22-25mm

29
Q

How do you calculate cardiac index?

A

Cardiac output/body surface area

where body surface area = square root of height x weight/36

30
Q

How do you calculate cardiac output?

A

MAP - MRAP*/SVR

where MAP = mean arterial pressure
MRAP = mean right arterial pressure

31
Q

How much mechanical power does a blood pump use?

A

1 watt

32
Q

What is the formula for power?

A

flow x pressure

33
Q

What is the rough frequency?

A

1-2 Hz

34
Q

What are the three requirements for full support?

A

Max flow rate = 8-10 L/min
Max pressure = 300 mmHg
Max ejection volume = 70-80mL

35
Q

What does partial support involve?

A

BiVAD doesn’t cover the entire CI range.
LVAD fully supports left ventricle but not right.
LVAD partially supports left ventricle.

36
Q

Why does partial pulsatile support need to be synchronised with an ECG?

A

The pump can wait for a period of time before injecting - which allows the left ventricle to pump normally and prevent back flow through the valve. Synchronisation assures that the LVAD ejects blood when the aortic valve is closed.

37
Q

What is the most important part of blood compatibility?

A

Striking the right balance between thrombus formation and hemolysis.

38
Q

What is thrombus formation? What does a high thrombus formation mean?

A

Shear stress too low. Stagnant flow.

39
Q

What is hemolysis? What is a normal value?

A

Shear stress too high. 0.8-1.2 N/m^2

40
Q

What is the max physiological stress within the cardiovascular system?

A

10 N/m^2

41
Q

What is the threshold for endothelial cell damage?

A

40 N/m^2

42
Q

What are typical values for the viscosity of normal human plasma at 37 degrees?

A

1-2 Ns/m^2

43
Q

How much free hemoglobin does the body remove per day?

A

20g: 14g by renal clearance and 6g by the reticuloendothelial system.

44
Q

What can increased hemoglobin cause? (5)

A 
Endothelial cell dysfunction
Vasomotor instability
Increased blood pressure
Renal damage
Activation of platelets
45
Q

How do we test our synthetic heart for blood compatibility?

A

Shear rate studies
Hemolysis
Thrombus formation

46
Q

What does flow studies involve? (5)

A 
Laser anemometry
Particle Visualisation
Surface washout
Stagnation areas
Valve flow
47
Q

What is laser anenometry?

A

Measures velocity at a single point

48
Q

What is the normal index of hemolysis (NIH)?

A 
[Hb x V x (100 - Ht)]/[QT/100]
where Hb = increase in free hemoglobin
V = total volume of blood
100-Ht = hematocrit
Q = flow rate
T = time
49
Q

What is the hemolysis rate index?

A

HRI = HbV(100-Ht)/T

50
Q

What are the three things to consider when thinking about tissue compatibility?

A

Material
Mechanical anchoring
Contact pressure

Heart Implants (2 decks)

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