Ventricular Function

Question 1

What are the four determinants on ventricular performance?

Answer 1

• Preload i.e EDV, stretch of muscle prior to contraction
• Afterload, the pressure at which the valves open
• inotropic state
• chronotropic state

Question 2

Preload

Answer 2

As EDV increases, SV increases as well the the maximum potential pressure,

Question 3

Afterload

Answer 3

If you increase the afterload (eg systemic hypertension), the SV is decreased.
Note that fibre tension is important also (law of Laplace, T proportional to P x r)

Question 4

Heart rate

Answer 4

Increasing heart rate will increase CO, an increase the inotropic state (force frequency relation) and decreases SV as reduced filling time.

Question 5

How do the left and right side of the heart balance?

Answer 5

Both sides must pump the same SV, eg afterload increases the preload:-

e.g. an increase in the MABP will decrease SV, thus increasing lung blood volume, which will in turn then lead to a greater EDV which increases SV whilst RV continues pumping

Question 6

How can we assess ventricular performance?

Answer 6

Ejection fraction: lower EF would sow depressed contractility
dP/dt: the max rate of pressure rise can be used as an indicator
end systolic P/V relation:
ventricular function curves: stroke work against LV EDP (preload)

Question 7

What is stroke work

Answer 7

SW is the MABP x the SV (technically the integral of the rate of pressure change per unit volume)