Cardiac Performance Flashcards
Cardiac Output eqn
CO = HR x SV
heart rate x stroke volume
Stroke Voulme eqn
SV = EDV - ESV
Regulation of EDV and ESV determine what?
cardiac performance
3 regulators of Cardiac Performance
1) preload
2) afterload
3) contractility
Preload is?
Vol of blood inside and tension of heart chamber before contraction.
Wall stress at end diastole
Frank-Starling Law
↑ stretch = ↑ contraction force
stretch depends on preload
Summation and recruitment do not occur in which type of mm?
cardiac
Cardiac mm does or does not fxn at the peak of length-tension?
Does not
Stretch causes ↑ tension how? (3)
1) overlap of think/thin filaments (lines myosin up with correct location on actin)
2) ↑ Ca2+ sensitivity (stretch of troponin ↑ desire to bind Ca2+)
3) ↑ Ca2+-induced Ca2+ release by activating stretch-activated Ca2+ channels
Stiffness of cardiac mm affects tension how? (2)
1) high resting tension
2) small ∆ in length produces large ∆ in tension
↑ in LV End Diastolic Fiber Length will ↑ what?
Stroke Volume
Preload influenced by? (3)
1) vent filling time
2) vent compliance
3) atrial systole
Preload dictates?
vent filling pressure
↑ heart rate affects vent filling time how?
↓ length of reduced filling phase = ↓ EDV and ↓ SV
Mechanism that preserves SV when HR ↑?
Contractility (via sympathetic stim)
Compliance is? Compliance eqn?
Heart’s ability to distend under pressure.
C=∆vol/∆pressure
Inability for Compliance leads to?
↓ ED fiber length, ↓ SV
Atrial Systole fills vent how much at rest?
10-20%
Atrial Systole most important for?
↑ HR (e.g. exercise).
Contributes ~40% of SV
Afterload is?
Mean Aortic Pressure
Pressure req’d for vent to eject blood
Afterload affected by? (3)
Factors that oppose vent ejection:
1) Peripheral Resistance
2) Blood Viscosity
3) Valvular Dysfxn (e.g. stenosis, insufficiency)
↑ Afterload means ↑ pressure needed to do what?
pressure req’d to eject blood
Mean Aortic Pressure eqn
MAP = Pdia + 1/3 (Psys-Pdia)
Pressure-Vol loops provide info about what?
Vent performance
4 phases of Press-Vol loop?
1) Isovolumetric contraction (contr against closed chamber)
2) Vent ejection
3) Isovol relaxation
4) Vent filling
Isovolumetric Contraction set up
(Pressure-Volume Loop)
Mitral and Aortic valves closed
Fixed vol of blood (vol is constant)
Huge LVP ↑
Vent Ejection set up
(Pressure-Volume Loop)
Mitral valve closed
LVP > aortic pressure Ѧ aortic valve opens
LVP stays ↑ thru contraction
LV vol ↓ significantly
Isovolumetric Relaxation set up
(Pressure-Volume Loop)
Systole ends Ѧ vent relaxes
LVP pressure < aortic pressure
Ѧ aortic valve closes
Closed valves = fixed ESV
Vent Filling set up
(Pressure-Volume Loop)
(Passive filling during vent and atrial diastole)
Myocardium relaxed LV press < atrial press
Mitral valve opens
Vent fills (passive & atrial contraction)
L vent vol ↑ back to EDV
What change can be made in P-V Loop to ↑ Preload?
↑ venous return -> ↑ LV filling and ↑ stretch
Ѧ ↑ SV (Frank-Starling mechanism)
What change can be made in P-V Loop to ↑ Afterload?
↑ aortic press (HTN) -> LV must eject against ↑ aortic press
Ѧ LV press must ↑ even more ->
aortic valve opens later and closes sooner
Ѧ ESV ↑, SV ↓
What change can be made in P-V Loop to ↑ Contractility?
Symp Stim -> ↑ LV press
Ѧ LV ejects more blood during systole (↑ SV)
Ѧ ESV ↓
Compliance allows vent to what?
Allows vent to have large ∆ in vol w/ small ∆ in pressure.
Cardiac performance dependent on regulation of what two things?
EDV and ESV
Pressure Volume Loop
