Question

A patient is given a large intravenous injection of norepinephrine that causes artery constriction, vein constriction, and direct actions on the heart. Describe how this would affect heart afterload, preload, and contractility. Given all of these effects, do you expect that cardiac output will increase, decrease, or not change? Be sure to explain your answer.

Answer 1

Afterload is the force against which ventricles contract and eject the blood.Afterload for left ventricle is determined by aortic pressure and afterload for right ventricle is determined by pressure in pulmonary artery. Norepinephrine causes artery and vein constriction. So it causes action.

Preload is the streching of cardiac muscle fibers at the end of diastole before contraction.

Contractility is the ability of tissue to shorten in length or contraction after recieving a stimulus.

Cardiac output directly proportional to preload and inversely proportional to afterload.