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Heart Implants > Study Questions > Flashcards

Study Questions Flashcards

1
Q

Define cardiac index and BSA.

A

Cardiac index is a cardiodynamic measure based on the cardiac output, which is the amount of blood the left ventricle ejects into the systemic circulation system in one minute.
BSA = body surface area

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2
Q

How do you calculate CI and BSA?

A

Cardiac output/body surface area

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

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3
Q

What are typical values for flow and pressure for an LVAD?

A

l

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4
Q

What are typical values for flow and pressure for a TAH?

A

8-10 L/min

300mmHg

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5
Q

Why do TAH designs very often preserve native atria?

A

l

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6
Q

What are the advantages of continuous flow LVADs over pulsatile flow designs?

A

Partial pulsatile support needs to be synchronized with ECG.
Non-pulsatile: membrane doesn’t have to move as you are continuously pushing blood through and not pumping back and forth.

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7
Q

Define hemolysis.

A

Shear stress too high.

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8
Q

What are the indicators of hemolysis?

A 
grey-blue colouring of nails
pale skin
jaundice
fever
dizziness
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9
Q

When does thrombus formation occur inside the LVAD, TAH chamber?

A

Stagnant flow

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10
Q

What methods are used to measure velocities inside the TAH, LVAD protoype?

A

Laser anemometry

Particle tracing

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11
Q

How do we define input impedance of the cardiovascular system?

A

Flow and pressure are not in sync, they are not in phase.

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12
Q

What animal models are used for TAH and LVAD studies?

A

Calves - TAH

Goats, sheep, rats (LVAD)

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13
Q

What is the major difference between electric current in the human body and conventional electronic devices?

A

For each frequency the phase difference and amplitude ratios are different.

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14
Q

Define NIH.

A 
Normal Index of Hemolysis:
[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
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15
Q

Define HRI.

A

Hemolysis Rate Index:

HRI = HbV(100-Ht)/T

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16
Q

Why does partial support with LVAD 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.

17
Q

What are the two typical ways of connecting LVAD to the circulatory system?

A

Atrium to aorta
Apex to aorta
Apex to abdominal aorta.

18
Q

What are the typical values for SVR and PVR?

A

SVR: 24.6-29.8 Wood Units
PVR: 2.8-3.9 Wood Units

19
Q

What feature of the circulatory system is represented by the windkessel model?

A

Rate of flow in aorta = rate of change of elastic chamber + rate of outflow into rigid tube

20
Q

What are the advantages of the distributed model of the circulatory system over the windkessel model?

A
  1. The effect of arterial distension on pressure wave velocity can be measured.
  2. Pressure wave reflections from impedance mismatches can be separated.
21
Q

What is the average shear stress in the human circulatory system?

A

0.8 - 1.2 N/m^2

22
Q

At what rate can the human body clear itself of free hemoglobin?

A

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

23
Q

Why does the optimization of the blood pump need to keep a proper balance between pressure, turbulence, shear rate and shear stress?

A

l

24
Q

What is the only FDA approved application of TAH?

A

SynCardia

25
Q

What are the advantages of receiving TAH prior to transplant? (6)

A

9.5 L/min through both ventricles
79% bridge to transplant rate
faster bridge to transplant
eliminates complications caused by a failing heart
hospital reimbursement
patient’s body automatically adjusts blood flow

26
Q

Intra-aortic balloon pump - principles of operation.

A

Increases myocardial oxygen perfusion and cardiac output.

Heart Implants (2 decks)

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