Ventricular Function Flashcards
Equation for stroke volume?
SV = EDV - ESV
Equation for CO?
CO = HR x SV
Ventricular diastole begins with? Then what happens
Closure of the semilunar valves.
Followed by “isovolumic relaxation” that ends when atrial pressure > ventricular pressure.
“Rapid filling” with opening of AV valves.
“Reduced filling/diastasis”, with a length determined by HR.
Terminated by atrial systole
How can you observe the effect of diastolic filling. Draw
Ventricular P-V relationship. Non-linear and passive. Drawn
Draw systolic P-V relationship
…
Draw the complete ventricular P-V loop
…
Four Determinants of ventricular performance
1) Preload
2) Afterload
3) Inotropic state
4) Heart rate
Preload is?
What happens as it increases
The degree of filling (EDV), and the stretch of muscle before contraction
-determines filament overlap (L-T relationship)
As it increases: SV increases, maximal potential pressures increases (FS mechanism!)
Afterload is?
Pressure at which valve opens. Pressure against which ventricle contracts (P in aorta, MAP)
- Systolic LV pressure or aortic pressure a main determinant.
- Fibre tension/myocyte stress is also important
Incr afterload > incr preload > decr SV
Inotropic state.
ABility of myocardium to contract with given preload/afterload. Force of contraction
Easiest way to measure preload?
To use LV (EDP) as a measure. It’s really hard to measure actual volumes
Systemic hypertension an example of
increased afterload. SV actually decreases
Wall stress (tension/thickness) is proportional to…?
(P x r / thickness)
ventricular filling is the portion most affected by changed chronotropy, circle this on an ECG. Why is this most affected?
…
The force of contraction increases as HR increases.
BUT with a high HR, SV is reduced due to reduced filling time.
R-R interval? How is this affected by HR?
Time for complete cardiac cycle. As HR increases this interval steadily decreases
How is time for Isovolumic contraction/relaxation affected by changing HR
It isn’t. remains very steady
Diastolic interval? How does this change?
Time for ventricular filling. Greatly reduced as HR increases
Balance of the Left and Right sides of the heart
- No matter the changes, as the system is closed, both sides of the heart pump the same volume OVER TIME.
- So changes affect BOTH sides.
- Balance is affected by arrhythmias
Bc heart is a balanced system, increased afterload >
> > increased preload
- inc P in aorta > inc LV afterload
- initially dec LV V
- RV continues pumping
- Blood accumulates in lungs
- inc stretch of capacitance circuit
- Filling P to LV inc
- Next beat LV EDV increases (preload)
- SV increases
Draw the closed system and an example of the things in it that affect
…
Factors that affect Preload
MANY! Blood volume, venous tone, posture, HR, atrial contraction
These will ALL affect the amount of blood loaded into the ventricles during the diastolic phase
Factors that affect Afterload
- Hypertension
- Vasoconstriction
- Aortic stenosis (narrowed valve)
- LV geometry
- Heart failure
Factors that affect Chronotropic State
Neural (ANS)
Catecholamines (eg PKA)
increased HR= + chronotropic state
Decreased HR = - chronotrpic state
How do we assess Ventricular function
We look at the Ejection fraction (55-75%) Peak dP/dt End-systolic PV relation Ventricular function curves
Ejection fraction equation, and how it’s determined
EF% = (EDV-ESV) / EDV x 100
Usually determined from echocardiogra or cardiac MRI data
Normal EF (LV): 55-60% at rest, to 85% during exercise
Depressed contractility if EF
max rate (dP/dt) of LV pressure is used as an indicator of contractility
+ during contraction
- during relaxation
The steeper the gradient, the faster the rate of pressure increase. THat’s why its more positive/narrow during systole as the pressure increase is faster then relaxation phase
End systolic P-V relation
The gradient is a boundary line for ESV. Ventricular function can be measured from the gradient
+ inotropic stimulus: Gradient steeper
- inotropic stimulus (eg heart disease, less pressure/force can be generated) : shallow gradient
LV EDP indication of
EDV, just easier to measure
Stroke WOrk
Work performed each cardiac cycle to eject blood under pressure into the aorta and pulmonary artery.
SW = P(MAP) x SV
or
SW = integral of P x volume change (dV) estimated by MAP x SV
Altered inotropic state changes?
End-systolic PV relationship and therefore the maximum pressure that can be developed
An increased HR leads to
Increased CO (CO = HR x SV)
Increased inotropic state
Decreased SV due to reduced filling tome
