Hypertension

By Doc Armalite on Dec 8, 2007 | Reply

You’re on the right track, but you haven’t got it right yet. Calcium is neccessary in muscle fibers (cells) to contract. I believe calcium channel blockers block the entry into smooth muscle cells, in the walls of arterioles, from the plasma. This decreases contraction by these fibers, and thus decreases vasoconstriction. The result is vasodilatation. This expansion of the lumens (the hole inside the small artery on cross section) of arterioles all over the body, decreases peripheral vascular resistance, and this lowers the blood pressure. Whew! These drugs may also decrease the contractility or strength of contraction of the heart, which would tend to lower blood pressure as well. Now as far as the precise subcellular mechanism, I’m a little rusty. I’m sure it’s available if you google it in. I’m just giving you what I know as a practicing ER doc. My favorite class of drugs for lowering blood pressure are the ARBs (angiotensin receptor blockers). I don’t believe that the calcium channel blockers ever lower the serum calcium. I’ve never noticed that. I know that if a patient is overdosed on calcium channel blockers, you can reverse it somewhat by giving IV calcium. In addition to their use for lowering blood pressure, some calcium channel blockers are used to slow the ventricular rate in supraventricular tachycardias, such as paroxysmal supraventricular tachycardia, atrial flutter, and atrial fibrillation. We always have some concern with these drugs, if the patient has some heart failure, ie. a weak heart muscle, in that they may decrease the contractility of the heart and throw them into overt heart failure. We don’t have that concern with the ACE inhibitors and the ARB’s. The ACE inhibitors have a frequent side effect of causing a nagging cough, because they cause a buildup of histamine, but the ARB’s don’t have that problem.