HYPERTENSION

Blood pressure is distributed in a typical bell-shaped curve within the overall population (Fig. 28-2) . As seen in the 12-year experience of the almost 350,000 men screened for the Multiple Risk Factor Intervention Trial (MRFIT), the long-term risks for cardiovascular mortality associated with various levels of pressure rise progressively over the entire range of blood pressure, with no threshold that clearly identifies potential danger. Therefore, the definition of hypertension is somewhat arbitrary and usually taken as that level of pressure associated with a doubling of long-term risk. Perhaps the best operational definition is "the level at which the benefits (minus the risks and costs) of action exceed the risks and costs (minus the benefits) of inaction."
The issue of what blood pressure level should be taken to signify hypertension is further complicated by its typically marked variability. Such variability is seldom recognized by the relatively few office readings taken by most practitioners but can easily be identified by automatically recorded measurements taken throughout the day and night (Fig. 28-3) . This variability can often be attributed to physical activity or emotional stress but is frequently without obvious cause.
In a few patients, markedly elevated levels clearly indicate serious disease requiring immediate treatment. However, in most cases, initial readings are not high enough to indicate immediate danger, and the diagnosis of hypertension should be substantiated by repeated readings. The reason for such caution is obvious: The diagnosis of hypertension imposes psychological and socioeconomic burdens on an individual and usually implies the need for commitment to lifelong therapy.
Both transient and persistent elevations in pressure are common when it is taken in the physician's office or hospital. To identify "white coat" hypertension, more widespread use of out-of-the-office readings, either with semiautomatic inexpensive devices or with automatic ambulatory recorders, is encouraged both to establish the diagnosis and to monitor the patient's response to therapy.[1] A large body of data provides normal ranges for both home self-recorded[7] and automatic ambulatory measurements.[8] Both average about 10/5 mm Hg lower than the average of multiple office readings. A closer correlation between the presence of various types of target organ damage, specifically, left ventricular hypertrophy (LVH), carotid wall thickness, proteinuria, and retinopathy, has been noted with ambulatory levels than with office levels.[9] However, in the absence of adequate long-term follow-up evidence of the risks associated with either home or ambulatory monitoring, office readings should continue to be the basis for the diagnosis and management of hypertension.