Study Questions Flashcards
Define cardiac index and BSA.
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
How do you calculate CI and BSA?
Cardiac output/body surface area
where body surface area = square root of height x weight/36
What are typical values for flow and pressure for an LVAD?
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What are typical values for flow and pressure for a TAH?
8-10 L/min
300mmHg
Why do TAH designs very often preserve native atria?
l
What are the advantages of continuous flow LVADs over pulsatile flow designs?
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.
Define hemolysis.
Shear stress too high.
What are the indicators of hemolysis?
grey-blue colouring of nails pale skin jaundice fever dizziness
When does thrombus formation occur inside the LVAD, TAH chamber?
Stagnant flow
What methods are used to measure velocities inside the TAH, LVAD protoype?
Laser anemometry
Particle tracing
How do we define input impedance of the cardiovascular system?
Flow and pressure are not in sync, they are not in phase.
What animal models are used for TAH and LVAD studies?
Calves - TAH
Goats, sheep, rats (LVAD)
What is the major difference between electric current in the human body and conventional electronic devices?
For each frequency the phase difference and amplitude ratios are different.
Define NIH.
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
Define HRI.
Hemolysis Rate Index:
HRI = HbV(100-Ht)/T
Why does partial support with LVAD need to be synchronised with an ECG?
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.
What are the two typical ways of connecting LVAD to the circulatory system?
Atrium to aorta
Apex to aorta
Apex to abdominal aorta.
What are the typical values for SVR and PVR?
SVR: 24.6-29.8 Wood Units
PVR: 2.8-3.9 Wood Units
What feature of the circulatory system is represented by the windkessel model?
Rate of flow in aorta = rate of change of elastic chamber + rate of outflow into rigid tube
What are the advantages of the distributed model of the circulatory system over the windkessel model?
- The effect of arterial distension on pressure wave velocity can be measured.
- Pressure wave reflections from impedance mismatches can be separated.
What is the average shear stress in the human circulatory system?
0.8 - 1.2 N/m^2
At what rate can the human body clear itself of free hemoglobin?
20g per day: 14g by renal clearance and 6g by the reticuloendothelial system
Why does the optimization of the blood pump need to keep a proper balance between pressure, turbulence, shear rate and shear stress?
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What is the only FDA approved application of TAH?
SynCardia
