Part 4: Drugs affecting the cardiovascular system.
If the pressure becomes too high, the person is said to be hypertensive. If the pressure becomes too low and blood cannot be delivered effectively, the person is said to be hypotensive. Helping the patient to maintain the blood pressure within normal limits is the goal of drug therapy.
When a person’s blood pressure is above normal limits for a sustained period, a diagnosis of hypertension is made. Untreated hypertension increases a person’s risk for the following conditions: coronary artery disease, and cardiac death, stroke, heart failure, renal failure and peripheral vascular disease. The classification scheme used to categorize individual cases of hypertension has been simplified to the following four stages based on blood pressure measurements: normal, prehypertension, stage 1 hypertension, and stage 2 hypertension.
Hypertension can also be defined by its cause. When the specific cause of hypertension is unknown, it may be called essential, idiopathic, or primary hypertension. About 90% of cases of hypertension are of this type. Secondary hypertension accounts for the other 10%. Secondary hypertension is most commonly the result of another disease such as pheochromocytoma (adrenal tumor), preeclampsia of pregnancy, or renal artery disease. It also may result from the use of certain medications. If the cause of secondary hypertension can be eliminated, blood pressure usually returns to normal.
If blood pressure becomes too low, the vital centers in the brain, as well as the rest of the tissues of the body, may not receive enough oxygenated blood to continue functioning. Hypotension can progress to shock, in which the body is in serious jeopardy as waste products accumulate and cells die from lack of oxygen. Hypotensive states can occur in the following situations:
• When the heart muscle is damaged and unable to pump effectively.
• With severe blood loss, when volume drops dramatically.
• When there is extreme stress and the body’s levels of norepinephrine are depleted, leaving the body unable to respond to stimuli to raise blood pressure.