What is it?
Hypertension is a persistent elevation in blood pressure that taxes the heart and can, over time, cause damage to organs such as the kidneys, brain, eyes, and heart. Blood pressure (BP) is the amount of force blood exerts on the walls of the arteries and veins. BP depends on the force and rate of the contraction of the heart as it pumps oxygenated blood from the left ventricle (compartment) of the heart into the arteries and the resistance to that flow. The amount of resistance depends on the elasticity and diameter of the blood vessels and how much blood is flowing through them.
Blood pressure is dynamic; it rises and falls depending on a person’s level of activity, time of day, and physical and emotional stresses. In healthy people, it is largely controlled by the autonomic nervous system, regulated by hormones produced by the adrenal gland that affect the amount of sodium, potassium, and fluids excreted by the kidneys (which affects the volume of blood) and is altered by decreasing and increasing the rate of the heart and dilating or constricting the blood vessels. When one or more of the regulating factors is not able to respond appropriately to the demands of the body, then the pressure of the blood may become persistently increased.
Two pressures are measured when blood pressure is evaluated. They are systolic pressure – the peak amount of force exerted on the blood vessel walls when the heart is contracting – and diastolic pressure – the amount of pressure present when the heart is relaxing between beats. Both are measured in millimeters of mercury (mm Hg) and are expressed as systolic over diastolic pressure. For instance, a blood pressure of 120/80 mm Hg corresponds to a systolic pressure of 120 and a diastolic pressure of 80 and would be reported as 120 over 80. Blood pressures are on a continuum but are generally classified in adults as follows:
Normal blood pressure - a systolic of less than 120 and diastolic of less than 80 mm Hg
Prehypertension (a state of blood pressure that is elevated above normal and that may eventually become hypertension) - a systolic pressure between 120-139 and/or a diastolic between 80-89 mm Hg
Hypertension, Stage 1 - a systolic of 140-159 and/or a diastolic of 90-99 mm Hg
Hypertension, Stage 2 - a systolic of 160-179 and/or a diastolic of 100-109 mm Hg
Severe hypertension, Stage 3 – a systolic greater than or equal to180 and/or a diastolic greater than or equal to 110 mm Hg
Usually, diastolic pressures will mirror systolic pressures, but as people age, the diastolic pressure tends to level out and hypertension that involves primarily the systolic pressure (called isolated systolic hypertension) becomes more common. In general, the greater the blood pressure for extended periods of time, the greater the potential for damage. Normal blood pressures for children are evaluated separately; they are compared to the 95th percentile of their peers, based on their age, height, and gender.
In most cases, the cause of hypertension is idiopathic (not known). This form of high blood pressure is called essential or primary hypertension. It can affect anyone but is found more frequently in men, especially those of African descent, and it becomes very common in all Americans as they age. The National Heart, Lung, and Blood Institute estimates that as many as 1 in 3 Americans will develop high blood pressure, but about 1/3 of those affected do not know that they have it. In most cases, high blood pressure does not cause symptoms until it begins to damage body organs. For this reason, hypertension is sometimes referred to as the “silent killer,” quietly increasing the risk of developing stroke, heart disease, heart attack, kidney damage, and blindness. Because it is both a quiet and a common condition, blood pressure is usually evaluated each time a patient sees their doctor.
Although it may not be possible to identify the cause, there are several things that are known to increase the risk of developing hypertension and that are known to exacerbate it when it is present. These include:
Obesity
Sedentary lifestyle
Smoking
Excessive use of alcohol
Excessive dietary sodium
Use of oral contraceptives
Use of drugs such as steroids, cocaine, and amphetamines
Hypertension may also be due to an identifiable underlying condition. This form of high blood pressure is called secondary hypertension. It is important to identify these underlying conditions as they may be able to be resolved and/or controlled, allowing the blood pressure to return to normal or near normal levels. These conditions include:
Kidney disease or damage – decreases the removal of salts and fluids from the body, increasing blood volume and pressure. Since hypertension can also cause kidney damage, this can be a progressive problem if left untreated.
Heart disease – this may affect the force and rate of the heart’s contraction. This can also be progressive.
Diabetes – this condition can damage the kidneys and affect the integrity of the blood vessels over time.
Arteriosclerosis – a hardening of the arteries that limits their ability to dilate and constrict
Cushing’s syndrome – a disorder that involves increased production of the hormone cortisol by the adrenal gland
Hyperaldosteronism (Conn's syndrome) – a condition characterized by an overproduction of aldosterone, a hormone that helps regulate the retention and excretion of sodium by the kidneys; it may be due to an adrenal gland tumor (usually benign)
Pheochromocytoma – a tumor of the adrenal gland (rare and usually benign) that produces excessive amounts of epinephrine, a hormone that the body uses to help it respond to stress; affected patients often have severe episodes of hypertension
Thyroid disease – both excessive and deficient amounts of thyroid hormone production can cause increases in blood pressure
Pregnancy – hypertension may develop at any time during a woman’s pregnancy but is most common during the last trimester, when it can cause pre-eclampsia (toxemia), a condition characterized by increased blood pressure and retention of fluids.
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