Ventricular Function

Question 1

Equation for stroke volume?

Answer 1

SV = EDV - ESV

Question 2

Equation for CO?

Answer 2

CO = HR x SV

Question 3

Ventricular diastole begins with? Then what happens

Answer 3

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

Question 4

How can you observe the effect of diastolic filling. Draw

Answer 4

Ventricular P-V relationship. Non-linear and passive. Drawn

Question 5

Draw systolic P-V relationship

Answer 5

…

Question 6

Draw the complete ventricular P-V loop

Answer 6

…

Question 7

Four Determinants of ventricular performance

Answer 7

1) Preload
2) Afterload
3) Inotropic state
4) Heart rate

Question 8

Preload is?

What happens as it increases

Answer 8

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!)

Question 9

Afterload is?

Answer 9

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

Question 10

Inotropic state.

Answer 10

ABility of myocardium to contract with given preload/afterload. Force of contraction

Question 11

Easiest way to measure preload?

Answer 11

To use LV (EDP) as a measure. It’s really hard to measure actual volumes

Question 12

Systemic hypertension an example of

Answer 12

increased afterload. SV actually decreases

Question 13

Wall stress (tension/thickness) is proportional to…?

Answer 13

(P x r / thickness)

Question 14

ventricular filling is the portion most affected by changed chronotropy, circle this on an ECG. Why is this most affected?

Answer 14

…
The force of contraction increases as HR increases.
BUT with a high HR, SV is reduced due to reduced filling time.

Question 15

R-R interval? How is this affected by HR?

Answer 15

Time for complete cardiac cycle. As HR increases this interval steadily decreases

Question 16

How is time for Isovolumic contraction/relaxation affected by changing HR

Answer 16

It isn’t. remains very steady

Question 17

Diastolic interval? How does this change?

Answer 17

Time for ventricular filling. Greatly reduced as HR increases

Question 18

Balance of the Left and Right sides of the heart

Answer 18

• 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

Question 19

Bc heart is a balanced system, increased afterload >

Answer 19

> > 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

Question 20

Draw the closed system and an example of the things in it that affect

Answer 20

…

Question 21

Factors that affect Preload

Answer 21

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

Question 22

Factors that affect Afterload

Answer 22

• Hypertension
• Vasoconstriction
• Aortic stenosis (narrowed valve)
• LV geometry
• Heart failure

Question 23

Factors that affect Chronotropic State

Answer 23

Neural (ANS)
Catecholamines (eg PKA)

increased HR= + chronotropic state
Decreased HR = - chronotrpic state

Question 24

How do we assess Ventricular function

Answer 24

We look at the 
Ejection fraction (55-75%)
Peak dP/dt
End-systolic PV relation
Ventricular function curves

Question 25

Ejection fraction equation, and how it’s determined

Answer 25

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

Question 26

max rate (dP/dt) of LV pressure is used as an indicator of contractility

Answer 26

+ 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

Question 27

End systolic P-V relation

Answer 27

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

Question 28

LV EDP indication of

Answer 28

EDV, just easier to measure

Question 29

Stroke WOrk

Answer 29

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

Question 30

Altered inotropic state changes?

Answer 30

End-systolic PV relationship and therefore the maximum pressure that can be developed

Question 31

An increased HR leads to

Answer 31

Increased CO (CO = HR x SV)
Increased inotropic state
Decreased SV due to reduced filling tome