**7. Ventricular function**

46 Special Topics in Cardiac Surgery

contraction phase when the LV is trying to overcome the resistance caused by the AEDP in order to open the Aortic valve. The aim of counterpulsation is to lower AEDP, thereby reducing afterload and myocardial oxygen consumption during isovolumetric contraction

Contractility is defined as the change in the force of contraction, independent of myocardial fiber length. Contractility inotropic performance can be increased by endogenous production of catecholamines or exogenous administration of vasopressors like norepinephrine (NE), dopamine, calcium etc. Myocardial contractility decreases wuth

hypoxemia and drugs like barbiturates, procainamide, lidocaine, propranolol etc.

Fig. 3. Starling Law

**6. Contractility** 

Fig. 4. Myocardial Oxygen Supply and Demand

(fig 4).

In order for us to appreciate the need for the IAB, we need to understand ventricular function, end diastolic volume and the Fick equation. Ventricular function in critical care is assessed by the Ejection Fraction (EF). EF is defined as the volume of blood ejected per beat (stroke volume or SV) divided by the volume in the LV prior to ejection, end diastolic volume (EDV). Stroke vol equals EDV minus end systolic volume (ESV). The equation for EF would then be:
