FRACP Madness: Pressure Volume Curves

Ok... Here is my attempt at simplifying Pressure - Volume curve. ESV = End Systolic Volume, EDV = End Diastolic Volume, SV = Stroke Volume, AV = aortic valve. Remember that this is pressure - volume curve for L ventricle only.

Varying the parameters. With increased end diastolic volume (as occurs during "filling"), you increase the cardiac output by increasing stroke volume (also contractility increases due to Sterling's Law). Increased afterload will decrease stroke volume, and conversely, decreased afterload will increase stroke volume (thus peripheral vasodilators are of use in cardiac failure).

Hence in ICU, it seems contradictory that you keep pumping fluids into people with heart failure, but this is exactly what they are trying to achieve in controlled environment - increasing the cardiac output by increasing preload and decreasing afterload...

This is what you get when you play around with inotropes...

Remember though:

SV = EDV - ESV

EDV is dependent on volume status and ventricular relaxation

ESV is dependent on contractility

CO = SV x HR
BP = CO x TPR = SV x HR x TPR = (EDV-ESV) x HR x TPR

Hence, when you are looking at BP, you are looking at:
1) Volume status
2) Contractility
3) Rate
4) Systemic vascular resistance