Eisenmenger complex is common in adult in –
Eisenmenger syndrome 

There are two different terms : -


Eisenmenger syndrome Refers to patients with a ventricular septal defect in which blood is shunted from right to left as a result of the development of pulmonary vascular resistance. This physiologic abnormality can also occur with ASP, atrioventricular septal defect, PDA or any other communication between aorta and pulmonary artery.
Eisenmenger complex Consists of pulmonary hypertension with a VSI providing the right to left shunt.


Eisenmenger physiology is defined by an absolute elevation in pulmonary arterial resistance to greater than 12 wood units or by a ratio of pulmonary to systemic vascular resistance of 1.0.
The pulmonary hypertension is the result of : -

a Early in the course it is due to markdely increased pulmonary blood flow —> Hyperkinetic pulmonary hypertension. This form of pulmonary hypertension decreases with the administration of pulmonary vasodilators or oxygen.
Li With the development of Eisenmenger syndrome pulmonary hypertension is due to pulmonary vascular obstructive disease, i.e., obstructive changes in the pulmonary vessels. This type of pulmonary hypertension only minimally responsive to pulmonary vasodilators or oxygen.