Pulmonary Edema | Symptoms, Causes and Treatment

6. ACE inhibitors

The Renin-Angiotensin-Aldosterone System (RAAS) acts to maintain blood pressure, blood volume, and systemic vascular resistance (how narrow the blood vessels are). Like many physiological mechanisms in the body, the “RAAS” may harm rather than heal the body.

A complex series of chemical reactions is initiated when the kidneys detect insufficient blood flow. Of particular interest is the formation of a potent peptide, Angiotensin II, by the enzyme Angiotensin Converting Enzyme (ACE). Angiotensin II is the main component of RAAS. It causes the blood vessels to narrow (Vasoconstriction), which makes it harder for the heart to pump against this increased vascular resistance. It also releases Aldosterone, a hormone that alters the constitution of urine, increasing the amount of fluids in the body. This eventually overloads the heart.

ACE inhibitors, such as Captopril, prevent the formation of Angiotensin II by blocking the action of Angiotensin Converting Enzyme (ACE). Therefore, these drugs decrease blood pressure, blood volume, and systemic vascular resistance. They are henceforth called “Afterload reducers”. Thus, the workload of the heart is decreased.