Lec 14-15 Cardiac Cycle Flashcards
How do preload and afterload affect cardiac output?
- high preload = increased cardiac output
- higher afterload = decreased cardiac output
How does Ca affect contraction strength?
small ca induced ca release [CICR] –> weak contraction
large CICR –> strong contraction
What two things does contraction strength depend on?
- Ca release
2. initial length [preload]
2 factors in force-length relation in intact heart?
- ventricular filling from veins/atria pre-stretches the ventricles [preload]
- ventricles must contract against existing arterial pressure [afterload]
When are LVP and aortic pressure closest?
at their peak, just at end of QRS is ST interval
LVP still > than aortic pressure
What causes mitral valve to open? to close?
open: LAP > LVP
close: LVP > LAP
What changes to pressure and volume between mitral valve closure and aortic valve opening?
- LVP gets bigger, volume stays the same = isovolumic contraction
What causes aortic valve to open? to close?
opens: when LVP > aortic pressure
closes: aortic P > LVP
What is happening to pressure and volume in left ventricle during ejection?
- pressure and volume both changing
What kind of relaxation in LV after aortic valve closes?
isovolumic relaxation
- volume is flat, pressure changes
What is first heart sound? and second?
first: closing AV valves [QRS wave]
second: closing aortic and pulmonary valves [just after T wave]
3 important principles illustrated by wiggers diagram?
- atrial P is low, Ventricular/aortic P is high
- valves only open when upstream P > downstream P
- heart sounds correspond to discrete events
Where are the 4 valves located [and names]
AV valves
tricuspid: RA –> RV
mitral [bicuspid]: LA –> LV
semi-lunar valves
pulmonary: RV –> pulm artery
aortic: LV –> aorta
Why are valves so important?
ensure unidirectional blood flow
4 phases of PV loop [including valve events]
MV closes 1. isovolumic contraction Aortic V opens 2. ejection Aortic V closes 3. isovolumic relaxation MV opens 4. diastolic filling
How to get SV [stroke volume] from EDV and ESV?
SV = EDV - ESV
How to get EF [ejection fraction] from SV and EDV?
EF [ejection fraction] = SV/EDV
What is the EDPVR? linear or non-linear?
- end-diastolic pressure-volume relationship
- nonlinear
- defines the lower boundary for end-diastolic P-V point of PV loop
What does the slow of the EDPVR mean?
on P-V graph: x axis = V, y axis = P
flatter = more compliant
steeper = less compliant
What does EDPVR nonlinearity mean?
low volume: small slope, ventricle compliant, easy to fill
high volume: large slope, ventricle stiff, difficult to fill
What is the ESPVR? linear or non-linear?
- end-systolic pressure-volume relationship
- linear
What do EDPVR and ESPVR do together?
define boundaries within which PV loop sites
independent of preload and afterload
Do EDPVR/ESPVR depend on preload and afterload?
No, they are independent
What is the preload? Two common ways to measure it? What point is it on PV loop?
- the load imposed on ventricle at end of diastole
- measured as end-diastolic volume [EDV] or end-diastolic pressure [EDP]
- the bottom right corner on PV loop
