High blood pressure causes

Whether young or old, each of us experiences changes in blood pressure throughout the day. It is usually lower at night when we sleep and higher during waking hours. Psychological stress can temporarily increase the pressure, although even a relaxed person in a quiet room may experience increased or decreased pressure for no obvious reason. Blood pressure also varies considerably among different individuals, tending to vary more widely in younger than in older people. This may reflect older persons' greater experience in coping with the contingencies of day-to-day living.

In addition to momentary fluctuations, the average blood pressure over a period of time also varies from one individual to another. It is this average pressure that physicians seek to determine and understand by measuring blood pressure several times during a single visit and again on successive visits, comparing readings to obtain an average. After the age of 40, systolic pressures of 140 or less are normal, pressures of 140 to 159 are considered borderline, and pressures exceeding 160 may signal an abnormality, especially if sustained over a period of time. At these ages, diastolic pressures under 90 are normal, pressures of 90 to 95 are borderline, and pressures greater than 95 are considered abnormal, indicating a need for further evaluation.

For the most part, psychological influences on blood pressure are transitory. Only rarely does psychological stress sustain an elevated pressure, the pressure usually dropping when the source of stress is removed. Excess salt, or sodium, is a more common cause of elevated pressure. Sodium apparently gets into arterioles, increases their contraction, and causes constriction.

Although the association is poorly understood, overweight also significantly contributes to high blood pressure. However, it is clear that when weight raises the blood pressure, reducing the weight also lowers the pressure.

Heredity is the principal contributor to the most common type of high blood pressure, known as essential or familial hypertension, which affects almost 90 percent of all people with excessive diastolic pressure. For this reason, a family history of high blood pressure is significant. This problem often first appears in middle life, but minor elevations in pressure during youth may give early clues. However, the mechanisms by which genes affect blood pressure are unknown.

Evaluation of high blood pressure usually includes a study of the kidneys because kidney disease is frequently associated with pressure problems. While this form of high pressure differs from essential hypertension, the essential type can damage the kidneys. In some cases it is difficult to determine whether high pressure preceded kidney disease, or vice versa.

In rare instances, mostly in young people, tumors of the adrenal gland cause high blood pressure. The possibility must be considered, but is usually quickly ruled out.