Hypertension (high blood pressure) is a highly prevalent and largely symptomless chronic medical condition that affects almost one in three adults living in industrialized nations. Hypertension is more prevalent among blacks than whites, with prevalence rates of black Americans among the highest in the world. Among whites, hypertension is more prevalent among males than females until age sixty-five, when females with hypertension begin to outnumber males. Among blacks, hypertension becomes more prevalent among females in comparison to males much earlier, beginning at age forty-five. Although prevalence rates of hypertension typically increase with age in industrialized countries, inhabitants of nonindustrialized countries maintain stable blood pressures across their life-span, suggesting that lifestyle factors associated with industrialization are associated with an increased propensity for developing hypertension. Prevalence rates for hypertension among Hispanic or Latino, Asian, and Native American populations are much lower than among white and black Americans.
There are two forms of hypertension: primary (or essential) hypertension and secondary hypertension. Essential hypertension represents the vast majority of cases and is characterized by chronically elevated blood pressure of unknown origin. In contrast, secondary hypertension is characterized by elevated blood pressures caused by another physiological abnormality, such as kidney disease, endocrine disturbances, or blockage of blood circulation. Regardless of form, hypertension is associated with increased risk for a number of diseases of the cardiovascular system, including coronary heart disease, stroke, peripheral artery disease, and congestive heart failure. Hypertension is therefore the primary cause of mortality in more than 10 percent of deaths among whites and more than 20 percent of deaths among blacks.
DIAGNOSING HYPERTENSION
The diagnosis of hypertension is typically made by a physician during a medical evaluation in a clinic setting. As part of this evaluation, measures of blood pressure are obtained by temporarily blocking blood flow in the brachial artery (upper arm) with an occluding cuff and listening to sounds of blood pulsations, called Korotkoff sounds, as arterial flow resumes. The first sound detected is associated with the magnitude of arterial pressure during cardiac contraction and is called systolic blood pressure (SBP). The disappearance of the Korotkoff sounds that occurs when blood flow returns to normal is associated with the magnitude of arterial pressure during cardiac refilling and is called diastolic blood pressure (DBP). Measures of SBP that are less than 120 millimeters of mercury (mm Hg) and DBP that are less than 80 mm Hg are considered within the normal range. SBPs and DBPs higher than these values are associated with increased risks for cardiovascular disease consequences in a linear fashion; a diagnosis of Stage 1 hypertension is assigned for patients with SBPs between 140 and 159 mm Hg or DBPs between 90 and 99 mm Hg, and a diagnosis of Stage 2 hypertension is assigned for patients with SBPs greater than 160 mm Hg or DBPs greater than 100 mm Hg.
It is well established that blood pressures measured by health care professionals in clinic settings often bear little correspondence to blood pressures that occur during daily life, creating diagnostic dilemmas for health care providers. In some cases, patients exhibit high blood pressures in the clinic but normal blood pressures in other settings, a condition called "white coat" hypertension from the presumption that these patients display physiological stress reactions while having their blood pressure measured. Another group of patients exhibits normal blood pressures in the clinic setting accompanied by elevated blood pressures throughout daily life. This condition has been termed "masked" hypertension, as both physician and patient are unaware of the elevated blood pressures unless sophisticated automated blood pressure devices, called ambulatory blood pressure monitors, are used to assess blood-pressure levels throughout a normal day. "White coat" hypertension is typically associated with lesser risk for cardiovascular disease, while "masked" hypertension is associated with risk profiles comparable to patients with untreated hypertension.
STRESS AND HYPERTENSION
It is widely recognized that an exposure to stressful life events, such as enduring natural or human-made disasters, being employed in a highly stressful job, or living in conditions of socioeconomic deprivation, is associated with increased blood pressure. However, not all persons exposed to these types of stressful events or life situations develop hypertension. This suggests that individual difference factors exist that either increase or decrease vulnerability for developing hypertension. Individual difference factors associated with a risk for hypertension can be categorized into three types: demographic and historical developmental factors, modifiable psychological or behavioral factors, and modifiable social factors.
Demographic and historical developmental variables represent risk factors that cannot be modified by the individual. For example, it is well known that hypertension runs in families, suggesting a genetic contribution. A risk for hypertension associated with one’s age, gender, or race represents other factors that are not modifiable by the individual. Specific medical conditions such as diabetes mellitus or obesity are also associated with an increased risk for hypertension.
Several modifiable lifestyle behavioral factors are associated with an increased risk for hypertension; foremost among these are physical inactivity and excessive consumption of alcohol or sodium. Three psychological characteristics have also been associated with hypertension. First, hypertensive patients often exhibit higher rates of symptoms of depression, anxiety, and anger than persons with normal blood pressure, leading researchers to hypothesize that a negative affect is associated with an increased risk for hypertension. Second, hypertensive patients have been shown to express anger less effectively than persons with normal blood pressure, either displaying more overt aggression during confrontation or suppressing the expression of anger entirely. Third, hypertensive patients exhibit higher rates of emotional defensiveness than persons with normal blood pressures, indicating that this tendency to be out of touch with their emotions may play a role in their condition.
A few modifiable social environment factors have also been implicated in establishing risk for developing hypertension. Families of hypertensive patients, for example, have been characterized as exhibiting less social skill than those of non-hypertensive patients, particularly when handling conflict. Further, as with many other chronic medical conditions, a lack of social support is strongly associated with an increased incidence of hypertension.
No single demographic, modifiable psychological, or social environmental individual difference variable explains entirely why stress leads to hypertension, suggesting that a combination of factors explains the association between stress and hypertension. For example, several individual difference variables have been hypothesized to explain the high prevalence of hypertension among black Americans. First, increased sodium retention in response to stress has been observed among black Americans that some social epidemiologists believe results from adaptive physiologies of African ancestors who survived the middle passage from Africa to America. Second, the psychological construct of John Henryism, described as effortful active coping in the face of extreme adversity, has been directly associated with blood-pressure levels in some black American samples, particularly those of low socio-economic status. Finally, an exposure to the racism and discrimination that is frequently experienced by many black Americans represents a social environmental factor that has been linked to higher blood pressure. Although consistent support linking each of these three individual difference variables to hypertension is lacking, there is sufficient evidence to suggest that each affects blood-pressure levels for some black Americans and is partly involved in explaining their increased prevalence of hypertension.
The physiological mechanisms through which psychological, behavioral, and social factors influence the risk for hypertension are unknown, although the autonomic nervous system is thought to be involved. Evidence from animal studies and from prospective trials on humans has revealed that participants who exhibit exaggerated blood-pressure responses to stress are more likely to develop hypertension later in life. According to this reactivity hypothesis, psychological factors, like the experience or inappropriate expression of anger, promote the onset of hypertension only inasmuch as they result in elevated blood-pressure responses to stress, which are presumably driven by the autonomic nervous system. Based upon this hypothesis, a considerable amount of research has linked various risk factors associated with hypertension to the magnitude of blood-pressure reactivity to stress. For example, healthy offspring of hypertensive parents exhibit greater blood-pressure reactions to stress than offspring of non-hypertensive parents. Similarly, both overt aggression and anger suppression are associated with heightened blood-pressure reactions to stress, in contrast to the appropriate expression of anger. Although the exact pathway through which psychosocial risk factors exert their influence on blood pressure—regulating organs is still unknown, the reactivity hypothesis has provided important clues regarding how a psychological construct like suppressed anger could lead to a physiological disturbance of blood-pressure regulation.
TREATMENT OF HYPERTENSION
Because of the high prevalence and lethal consequences of hypertension, a number of interventions have been developed to lower blood pressure. The primary treatment strategy for both lowering blood pressure and reducing the risk of cardiovascular disease associated with hypertension consists of a variety of antihypertensive medications.
Although the various classes of medications operate through different physiological pathways, they all are potent blood pressure—lowering agents. Unfortunately, a large number of hypertensive patients do not take their medication as prescribed, partly because the side effects can be more noticeable than the condition of hypertension itself.
Several non-pharmacologic methods are known to lower blood pressure and have served as useful adjunct treatments for hypertensive patients and as primary preventive strategies for persons at risk for developing hypertension. Weight loss, typically achieved through a combination of dietary management and increased physical activity, can result in blood-pressure reductions comparable to antihypertensive medication. Sodium restriction and potassium supplementation also reduce blood pressures, particularly among patients who are sodium sensitive. Eliminating the consumption of alcohol is an effective means of lowering blood pressure among hypertensive patients who consume alcohol regularly.
Because psychological factors are linked to hypertension, the blood pressure—reducing properties of three psychological interventions have been examined: relaxation, biofeedback, and individualized stress-management programs. The magnitude of blood-pressure reductions observed with relaxation and biofeedback interventions is generally much lower than those observed with anti-hypertensive medication. Because stress-management approaches are individualized based upon the patient’s unique psychological profile, larger reductions in blood pressure have been observed.
Hypertension is a chronic medical condition with no single cause. By considering both pharmacologic and non-pharmacologic interventions with respect to each individual patient, effective intervention and prevention programs will help eliminate hypertension as a public health problem.
