Without a definite understanding of what causes essential hypertension, doctors often explain it as a malfunction of one or more parts of the blood-pressure regulatory system. Different factors increase blood pressure in different people. That's why a treatment that lowers blood pressure in one person does not always work in another. For example, a person who is "salt sensitive" usually can control his or her blood pressure with a low-salt (sodium) diet alone, while another person may find salt intake has little or no influence on blood pressure.
The Framingham Heart Study, which has tracked the health of participants since the late 1940s, found that 65 percent to 75 percent of people over age 65 with elevated blood pressure had isolated systolic hypertension.
In the past, doctors considered this type of high blood pressure to be normal in elderly patients, so normal that it wasn't even treated. However, a 1991 study, Systolic Hypertension in the Elderly Program (SHEP), provided strong evidence to the contrary. SHEP tracked 4,736 patients with isolated systolic hypertension over five years. Half the participants used drugs to lower their blood pressure, while the other half received a placebo (an inactive pill). The group taking medication had significantly fewer strokes and heart attacks than the placebo group. The SHEP study has spurred doctors to treat isolated systolic hypertension in older patients more aggressively.
If you or your doctor think you have "white-coat hypertension," you can use a home blood-pressure machine to check your blood pressure periodically over the course of a week or two.
People who are habitually affected by stress — whether from losing a job, feeling pressure at work or simply getting stuck in traffic — may develop high blood pressure that could inflict some of the same damage as full-time hypertension.
Malignant hypertension is an emergency. Anyone with malignant hypertension must be hospitalized immediately. It places people at immediate risk for heart attack, stroke, heart failure, permanent kidney damage, bleeding into the brain (hemorrhagic stroke) and brain swelling.
Malignant hypertension develops in less than 1 percent of people who already have high blood pressure. Rarely, the appearance of malignant hypertension is the first sign that a person has high blood pressure. The cause of this condition is usually unknown, but occasionally it can be a reaction of your body to a drug of abuse, like cocaine, or a reaction to stopping a blood-pressure medicine. Never stop taking blood-pressure medicine without your doctor's supervision; doing so might cause a sudden increase in your blood pressure.
High blood pressure in the first half of a pregnancy (the first 20 weeks) is called chronic hypertension in pregnancy. High blood pressure in the second half of pregnancy (weeks 20 through 40) could be any of the following:
- Chronic hypertension in pregnancy is high blood pressure caused by a condition unrelated to pregnancy (such as essential hypertension or secondary hypertension) that begins or continues during pregnancy. The rise in blood pressure may have predated the pregnancy by months or years. However, this rise is first noticed during pregnancy, when a woman who has not regularly visited a doctor gets prenatal care. Chronic hypertension in pregnancy continues after the baby is delivered. Women with chronic hypertension in pregnancy are at increased risk for developing preeclampsia.
- Gestational hypertension (or pregnancy-induced hypertension) is high blood pressure that results from the effects of the hormone estrogen. Blood pressure returns to normal within 12 weeks after the baby is delivered.
- Preeclampsia (or toxemia of pregnancy) causes tightening of arteries throughout the mother’s body and placenta, as well as unpredictable blood clotting. It not only creates high blood pressure but also causes fluid retention that leads to swelling of the feet and legs (and sometimes the hands and face), and protein in the urine. Preeclampsia can progress to cause neurological symptoms including seizures. Preeclampsia requires very close attention from your doctor and frequently requires the early delivery of the baby in order to keep both mother and baby safe from harm.
Sometimes it's not possible to know what causes blood pressure to rise during pregnancy until the pregnancy is over. Protein in the urine any time during pregnancy or in the first 12 weeks after delivery confirms preeclampsia. If high blood pressure goes away within 12 weeks of delivery, and there was never significant protein in the urine, the cause can be diagnosed as gestational hypertension. If high blood pressure does not go away after delivery, chronic hypertension is the culprit. It is even possible to have two causes of high blood pressure during pregnancy. For example, a woman with chronic hypertension may develop preeclampsia in the second half of her pregnancy.