Vasoconstriction is an excessive tightening of the blood vessels.
Hypertension is treated with two types of medications, vasodilators, which relax the blood vessels, or diuretics, which cause the kidney to lose fluid and decrease blood volume. Presently, neither variable is measured. Treating high blood pressure is a trial and error process of choosing from more than 50 drugs currently approved for hypertension therapy. However, some hypertensive patients may actually have a decreased blood volume. Giving such a patient a diuretic decreases the blood flow to the kidney, and damages organs.