How is high blood pressure defined?
Blood pressure can be affected by several factors, so it is important to standardize the environment when blood pressure is measured. For at least one hour before blood pressure is taken, avoid eating, strenuous exercise (which can lower blood pressure), smoking, and caffeine intake. Other stresses may alter the blood pressure and need to be considered when blood pressure is measured.
Even though most insurance companies consider high blood pressure to be 140/90 and higher for the general population, these levels may not be appropriate cut–offs for all individuals. Many experts in the field of hypertension view blood pressure levels as a range, from lower levels to higher levels. Such a range implies there are no clear or precise cut–off values to separate normal blood pressure from high blood pressure. Individuals with so–called pre–hypertension (defined as a blood pressure between 120/80 and 139/89) may benefit from lowering of blood pressure by life style modification and possibly medication especially if there are other risk factors for end–organ damage such as diabetes or kidney disease (life style changes are discussed below).
For some people, blood pressure readings lower than 140/90 may be a more appropriate normal cut–off level. For example, in certain situations, such as in patients with long duration (chronic) kidney diseases that spill (lose) protein into the urine (proteinuria), the blood pressure is ideally kept at 130/80, or even lower. The purpose of reducing the blood pressure to this level in these patients is to slow the progression of kidney damage. Patients with diabetes (diabetes mellitus) may also benefit from blood pressure that is maintained at a level lower than 130/80. In addition, African Americans, who have an increased risk for developing the complications of hypertension, may decrease this risk by reducing their systolic blood pressure to less than 135 and the diastolic blood pressure to 80 mm Hg or less.
In line with the thinking that the risk of end–organ damage from high blood pressure represents a continuum, statistical analysis reveals that beginning at a blood pressure of 115/75 the risk of cardiovascular disease doubles with each increase in blood pressure of 20/10. This type of analysis has led to an ongoing “Rethinking” in regard to who should be treated for hypertension, and what the goals of treatment should be.
Isolated systolic high blood pressure
Remember that the systolic blood pressure is the top number in the blood pressure reading and represents the pressure in the arteries as the heart contracts and pumps blood into the arteries. A systolic blood pressure that is persistently higher than 140 mm Hg is usually considered elevated, especially when associated with an elevated diastolic pressure (over 90).
Isolated systolic hypertension, however, is defined as a systolic pressure that is above 140 mm Hg with a diastolic pressure that still is below 90. This disorder primarily affects older people and is characterized by an increased (wide) pulse pressure. The pulse pressure is the difference between the systolic and diastolic blood pressures. An elevation of the systolic pressure without an elevation of the diastolic pressure, as in isolated systolic hypertension, therefore, increases the pulse pressure. Stiffening of the arteries contributes to this widening of the pulse pressure.
Once considered to be harmless, a high pulse pressure is now considered an important precursor or indicator of health problems and potential end–organ damage. Isolated systolic hypertension is associated with a two to four times increased future risk of an enlarged heart, a heart attack (myocardial infarction), a stroke (brain damage), and death from heart disease or a stroke. Clinical studies in patients with isolated systolic hypertension have indicated that a reduction in systolic blood pressure by at least 20 mm to a level below 160 mm Hg reduces these increased risks.