Question

Mr. Anderson has been experiencing very high blood pressure. His baroreceptor reflex has become adapted to this elevated blood pressure range and is no longer able to bring it back down into a normal homeostatic range. You have been asked to come up with a medical intervention that will help reduce Mr. Anderson’s blood pressure. Using the baroreceptor reflex in the Essentials figure, design a drug that will work to reduce Mr. Anderson’s elevated blood pressure. Be sure to explain what your drug is designed to affect and how it will reduce the patient’s elevated blood pressure

Answer 1

...First you need a clear understanding of what the baroreceptor reflex does in a NORMAL state. They are mechanoreceptors that fire neuronal signals when the cells of the aortic arch and carotid bodies stretch. These signals go to brain stem and do TWO SEPARATE BUT COMPLEMENTARY things: (1) They trigger a PARASYMPATHETIC response through the 10th cranial nerve that tells the heart to slow down and quit beating so hard. This decreases the cardiac output (stroke volume x heart rate). Blood pressure (aka mean arterial pressure) equals cardiac output x total peripheral resistance. So this first function (the parasympathetic response) helps with the first variable, cardiac output...............
(2) The other function of the baroreceptor reflex is to INHIBIT the peripheral SYMPATHETIC drive. The sympathetic nervous system affects blood pressure primarily by causing a constriction of most blood vessels. It also makes the heart beat harder and faster. By inhibiting this system, the reflex decreases the total peripheral RESISTANCE. It also further decreases cardiac output. So again, if MAP = CO x TPR, and the baroreceptor reflex to augment the parasympathetic response and suppress the sympathetic response, both CO and TPR will fall and thus MAP falls.
. Years of supraphysiologic pressure has stiffened and enlarged the muscular arteries and decreased the sensitivity of the mechano-receptors. What can you do? DRUGS! Basically, GIVE DRUGS THAT DO FOR THE BODY WHAT IT CAN NO LONGER PROPERLY DO FOR ITSELF. So.... you are looking for drugs that decrease cardiac output and/or TPR. The trick is finding a combination of effects that works, is safe for long-term use, and has minimal side effects. ..............
The drugs that save the most lives when treating hypertension are diuretics, which basically decrease fluid volume by making you pee out excess salt and water. Less volume in arteries=less pressure=decreased TPR. Beta-blockers can act on the heart to inhibit the sympathetic response, resulting in decreased stroke volume and HR (=decreased cardiac output). Other things like calcium channel blockers act on the arteries themselves to block sympathetic constriction, which decreases TPR. Any of these drugs will lower blood pressure. Diuretics are usually first-line monotherapy, with a lot of exceptions..........