What is high blood pressure?

Medically reviewed: 15, February 2024

Read Time:9 Minute

What is normal and high blood pressure?

High blood pressure (hypertension) is a prevalent chronic condition affecting millions of people worldwide, characterized by an increase in arterial pressure within the body’s vessels. Hypertension can have severe consequences for health, including risks of myocardial infarction, stroke, kidney failure, and other complications. Risk factors may include genetic predispositions as well as unhealthy lifestyle habits such as smoking, alcoholism, obesity, stress, and lack of physical activity. Our cardiology specialists offer comprehensive diagnostic and treatment services aimed at normalizing blood pressure, preventing complications, and improving patients’ quality of life. Explore our website to learn more about high blood pressure symptoms, causes, and treatment methods.

As late as the 1950s and 1960s, some physicians believed that an elevated blood pressure was necessary to provide an adequate blood supply to vital organs as people aged. Following the landmark Framingham Study and other epidemiologic studies (ie, Tecumseh, LA County), it became obvious, however, that as blood pressure increases even from levels of 110-115/75-80 mm Hg, the risk for cardiovascular events increases.

Risk increases more dramatically when pressures rise above 140/90 mm Hg. Therefore, an arbitrary number was assigned as a definition of hypertension: 140/90 mm Hg or above. Later, it became apparent that lowering pressure from above these levels decreases the incidence of cardiovascular events.

Classification of High Blood Pressure

For many years, it was also believed that diastolic blood pressure was more important than systolic in defining future cardiovascular risk. More recent data, however, have established that elevated systolic pressure may increase risk more than comparatively elevated diastolic pressure.

For example, in the Multiple Risk Factor Intervention Trial (MRFIT), where more than 300,000 men were tracked, systolic blood pressure (SBP) levels of 150 to 159 mm Hg conferred a greater relative risk for coronary heart disease events than diastolic blood pressure (DBP) levels of 95 to 100 mm Hg. Yet, many physicians will treat patients with these levels of DBP and not intervene until SBP levels are considerably higher.

High blood pressure: common risks

As noted, elevated systolic blood pressures (SBP) may impart greater risk for coronary heart disease (CHD) than diastolic blood pressures (DBP); ie, 140-149 mm Hg systolic blood pressure is greater risk than 90-94 mm Hg diastolic blood pressure.

In addition, it has been clearly established that isolated systolic hypertension, defined in some countries as 160 mm Hg systolic with 90 mm Hg or below diastolic, also increases risk not only for stroke and congestive heart failure, but for coronary heart disease events as well.

Of importance is the fact that lowering blood pressures from these levels decreases morbidity and mortality. Recent data have also established that isolated borderline systolic hypertension (ie, blood pressures of 140 to 159 mm Hg systolic with a diastolic below 90 mm Hg) also significantly increases risk for cardiovascular events and for the future development of more severe hypertension.

Patients with these levels of pressures should initially be treated with lifestyle modifications. If systolic blood pressure remains above 145 to 150 mm Hg, medication may be tried. There is no proof as yet that morbidity or mortality is reduced in these patients by specific treatment, but if blood pressure can be lowered with a simple regimen without side effects, it is probably worthwhile.

The Sixth Joint National Committee (JNC-VI) on Prevention, Detection, Evaluation and Treatment of High Blood Pressure redefined hypertension to conform to newer data defining risk. Optimal blood pressure in an adult was defined as below 120/80 mm Hg.

A category of high-normal was also defined, with diastolic pressures of 80 to 89 mm Hg and systolic pressures of 130 to 139 mm Hg. This designation did not suggest that patients who have these pressures should be vigorously treated; rather, they should be followed and periodically revaluated because they are at greater risk for cardiovascular disease than patients with lower pressures, especially if they have other risk factors for heart disease (ie, diabetes, hyperlipidemia, or a history of smoking).

The JNC-VI eliminated the stage IV classification (>/= 210 mm Hg/>/= 120 mm Hg) which had appeared in previous reports. Severe hypertension is relatively rare and the approach to therapy is similar at blood pressures of 180-190/100 mm Hg or 210/120 mm Hg except for patients with acute symptoms, ie, hypertensive urgencies or emergencies. The new classification reflects additional data.

The diagnosis of hypertension should not be made on one visit, unless pressures are above 160-170/105-110 mm Hg; treatment is clearly indicated in these instances. Pressures at levels lower than these should be checked several times over a 3- to 6-month period as lifestyle modifications are made.

In our experience, pressures return toward normal levels in approximately 20% to 25% of subjects with stage I hypertension.

“White-Coat” High Blood Pressure

There are approximately 20% of people whose pressures are higher in a doctor’s office than at home. These patients should not be ignored. They may already have physiologic changes when compared to people whose pressures are normal at home and in a doctor’s office:

  • Vascular resistance tends to be increased.
  • There may be evidence of left ventricular diastolic dysfunction.
  • From a chemical perspective, individuals with early hypertension exhibit similar characteristics as patients with increased insulin resistance and higher lipid levels.
  • More patients with “white-coat” hypertension are obese and have diabetes than normotensive (in office and at home) individuals.

The question arises, should patients be screened for “white-coat” or “office” hypertension and undergo ambulatory blood pressure monitoring or should decisions regarding treatment be made on the basis of office readings or, in some cases, home blood pressure recordings?

Based on available data and our own experience, we believe that office blood pressures are reliable indicators of outcome. If these pressures are not reduced to normal levels (< 140/90 mm Hg) during the 3- to 6-month period of observation, the patient should be treated with medication, no matter how high the pressures are in one’s home or workplace.

Ambulatory Blood Pressure Monitoring

It should be pointed out that all of the data upon which we base our estimates of risk were accumulated from casual blood pressure readings taken in an office or clinic. The higher the “casual pressure,” the greater the risk of a cardiovascular event. It should also be remembered that the data upon which we estimate benefit of treatment are also based on casual pressures.

In clinical trials such as the Systolic Hypertension in the Elderly Program (SHEP) and the Hypertension Detection and Follow-up Program (HDFP), pressures were taken in an office or clinic every 3 to 4 months; patients with the lowest pressures had the best outcome.

Ambulatory blood pressure monitoring has contributed information on the circadian rhythm of blood pressure, establishing that blood pressure decreases during sleeping hours and increases within an hour or two of arousal in the morning. It has helped to define a certain subset of patients whose pressures do not decrease from 2 AM to 6 AM. These so-called “non-dippers” are more likely to have left ventricular hypertrophy. This phenomenon is more common in the Black population.

There are also data suggesting that 24-hour blood pressures correlate more closely than office pressures with target organ involvement. But, although ambulatory monitoring has proved to be an interesting research tool and is useful in establishing the duration of action of new drugs, it was not recommended by the JNC-VI as a routine procedure in the initial evaluation of the hypertensive patient.

We agree with this recommendation and do not believe that the expense of this procedure is justified at this time. Nor do we believe that the data provided influences therapeutic decisions in the vast majority of patients.

Some patients want to know their blood pressure. In these cases, or in situations where symptoms are confusing (eg, dizziness. is this the result of pressures that are too high or too low?), pressures can be taken at home with an inexpensive sphygmomanometer.

A series of readings over time at different times of the day may actually provide more information than one 24-hour recording.

High Blood Pressure Diagnostic Evaluation

The JNC-VI, as have all previous Joint National Committees, suggested a relatively inexpensive and simple diagnostic evaluation. This includes a careful history, physical examination and blood chemistries that help to rule out not only renal failure (serum creatinine levels) but also a possible secondary cause of hypertension (eg, primary aldosteronism), by checking serum potassium levels. A lipid profile and blood glucose levels are also suggested to help identify other cardiovascular risk factors.

An Echocardiogram. Should It Be Done as a Routine Procedure?

An electrocardiogram was suggested by all of the JNCs to detect arrhythmias and evidence of ischemic heart disease. An echocardiogram has not been recommended as a routine procedure for the following reason: It was recognized that an echocardiogram is a more sensitive indicator of left ventricular hypertrophy than an electrocardiogram.

However, patients whose blood pressures remain above 140/90 mm Hg after several recordings and several months of lifestyle intervention should have their pressure lowered with medication, whether or not left ventricular hypertrophy is present.

In addition, although some investigators believed for many years that the presence or absence of left ventricular hypertrophy should be used as a guide for initial therapy, it has now been demonstrated in several recent studies that all of the drugs that are currently used as monotherapy, ie, diuretics, beta-blockers, ACE inhibitors, angiotensin II receptor blockers (ARBs), or calcium channel blockers, will reverse left ventricular hypertrophy if blood pressure is lowered.

However, ACE inhibitors (and possibly ARBs) and diuretics are probably more effective than the other agents. It is, therefore, unnecessary to order an echocardiogram in the initial evaluation of the hypertensive patient unless there is another specific indication for this procedure.

Additional studies over and above those may be necessary in:

  • Patients with hypertension who are below the age of 15
  • Elderly patients (> 65 years of age) with recent onset of moderately severe or severe hypertension
  • Individuals with persistent elevations of blood pressure after triple-drug therapy that includes a diuretic
  • People with hypertension and symptoms of headache, unusual patterns of sweating and palpitations.

In these instances, procedures to rule out renovascular disease, primary aldosteronism or pheochromocytoma should be undertaken. Details of these procedures can be found in any standard textbook on hypertension.


Patients with high blood pressure should be approached with a confident attitude that the complications that used to occur in many patients can be prevented. The diagnostic evaluation is relatively simple in the majority of cases and does not routinely require an echocardiogram or ambulatory blood pressure monitoring. In most cases, office blood pressures should be used to estimate risk and judge prognosis.

Some form of treatment should be undertaken in anyone whose blood pressures remain above 140/90 mm Hg after repeated observations. More attention should be paid to elevated SBPs than has been in the past.