By John Messmer, MD

Blood pressure is a complex physiologic subject, even for physicians. Despite more than 50 years of scientific research, oftentimes the fundamental cause is unknown. In some cases, hypertension results from dysfunction of some organ or an abnormal secretion of a biochemical compound. It can also be caused by medication, lifestyle choices, or a change in your physiology.

Two types of hypertension

When a patient's hypertension has no identifiable cause, it is called "essential" hypertension; when the hypertension is caused by some problem, it is called "secondary" hypertension.

1.   Essential hypertension

Essential hypertension is the most common type. It runs in families, and it is most prevalent in African-Americans. However, a person who has a genetic propensity for hypertension can reduce his risk-or at least make his hypertension milder or easier to treat-by making healthy lifestyle choices.

2.   Secondary hypertension

Secondary hypertension is caused by an identifiable problem. About 5% of cases are due to secondary hypertension from various causes.

Essential hypertension: Facts and variations

Regular exercise makes the heart a more efficient pump, so it can circulate blood under lower pressures. Although not all obese people develop hypertension, a normal weight ensures the blood is not passing through storage tissue (which requires more blood pressure). Being judicious with salt is also helpful. Some people are particularly susceptible to the blood pressure elevating effects of salt, but even people who are not salt sensitive can reduce their risk of organ damage by keeping their salt consumption lower.

Essential hypertension has some variations:

1.   White coat hypertension

White coat hypertension refers to the phenomenon of a person's blood pressure being high only in the doctor's office. Some authorities think this is a true form of hypertension. To determine whether treatment is needed, physicians may do a 24-hour ambulatory blood pressure exam. The person wears a small recorder and a blood pressure cuff. Pressure measurements are made at a specified frequency for 24 hours and the results analyzed. If blood pressure is high or trends high for a substantial part of the day, treatment may be recommended.

2.   Labile hypertension

Labile hypertension means the pressure goes from high to low to normal at various times. It can be tricky to treat because the medications that work when it is high may be too much for the low times. The patient must be a partner in management of labile hypertension to avoid under- or over-treatment.

3.   Malignant hypertension

Sometimes called accelerated or urgent hypertension, malignant hypertension is a medical emergency. In malignant hypertension, there is damage taking place at the time of presentation to medical care. Example emergencies are: an impending heart attack or heart failure, dissection (tearing) of an artery, deterioration of kidney function or a stroke in evolution. Usually systolic pressure exceeds 240 mm Hg or diastolic exceeds 120 mm Hg. This problem is treated in a hospital with powerful medications designed to lower blood pressure rapidly.

4.   Resistant hypertension

Hypertension is called "resistant" when it can not be controlled with maximum doses of several drugs. This is uncommon today as there are many effective and complementary medications to treat blood pressure. Some people believe resistant hypertension may be due to patients not taking medications properly perhaps trying to save money or because of side effects.

Secondary hypertension: Causes and triggers

Pregnancy induced hypertension

This is a special situation due to the hormonal changes of pregnancy. It can cause premature birth, low birth weights and can result in maternal seizures.

Kidney function hypertension

The kidney (which normally helps regulate blood pressure) can cause a type of secondary hypertension when there is a reduction in blood flow from a narrowed renal artery. Narrowing can develop from congenital thickening of the muscular wall of the artery or from cholesterol blockage. Narrowing of the renal artery lowers blood pressure to the kidney. The kidney responds as though the entire body's pressure is too low by secreting chemicals that cause the blood pressure to rise.

Raised blood pressure due to nonsteroidal anti-inflammatories

Over-the-counter medications, such as ibuprofen, aspirin and naproxen, can cause elevated blood pressure in some people (particularly older individuals) because these drugs reduce blood flow to the kidney.

Caffeine and blood pressure

Caffeine can affect blood pressure in some people.

Decongestants and the effect on blood pressure

Sometimes decongestants can raise blood pressure by direct stimulation of the heart and constriction of the small arteries in the extremities.

Real licorice and high blood pressure

Very large amounts of real licorice (not the typical candy sold in the United States which is flavored with anise) can cause blood pressure elevations.

Narrow aorta hypertension

Narrowing of the aorta, the largest artery, can be present at birth. This also reduces blood flow to the kidneys and can raise blood pressure just as when the renal artery is affected. Typically this condition shows up in adolescence.

Adrenal gland - a trigger for hypertension

The adrenal gland is the organ that responds when there is a renal cause of hypertension, but it can develop a tumor called a pheochromocytoma that secretes chemicals that raise blood pressure. In other circumstances, the adrenal may become overactive, causing the kidney to retain too much salt and water, which raises blood pressure.

Overactive thyroid and high blood pressure

An overactive thyroid can cause the heart to pump harder and faster with the result being an elevated blood pressure.

Remember: The complexity of hypertension requires an evaluation by a medical professional so that the proper diagnosis and therapy can be prescribed.