Active Control of Hypertension

Alfred A. Bove, MD with Carl Sherman

Series Editor: Nicholas A. DiNubile, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 4 - APRIL 98

In Brief: Hypertension is common, and even slight elevations in blood pressure can be associated with health risks. Regular aerobic exercise helps prevent hypertension. In patients who already have hypertension, such exercise has been shown to lower systolic and diastolic blood pressure by a mean of 10 mm Hg. For mild or labile hypertension, lifestyle modification that includes at least a half hour of moderate aerobic exercise at least 3 days a week should be tried before using drug therapy. If medication is needed, one that is not likely to impede the patient's ability to exercise should be considered.

Hypertension, generally defined as blood pressure persistently above 140/90 mm Hg, is extremely common, affecting nearly 1 American in 4 (1). Of even greater concern is that about 1 in 16 Americans has severe hypertension (2). Even mild blood pressure elevations are associated with an increased risk of myocardial infarction and stroke, and the risk rises continuously with the severity of the condition (3). Consequently, the prevention and treatment of hypertension are a high priority in medicine and public health.

It is well documented that blood pressure reduction with medication significantly reduces cardiovascular risk. But nonpharmacologic strategies for blood pressure reduction, including weight loss, dietary modification, and exercise, are also effective. Particularly when patients have mild to moderate hypertension, these strategies offer the possibility of reducing blood pressure and cardiovascular risk without any of the adverse side effects associated with medication.

With direct effects on circulation, metabolism, and the nervous system, exercise represents a multipronged assault on cardiovascular risk. Whether used only with other lifestyle changes or in combination with medication, exercise is a particularly attractive tool for hypertension control.

Evidence for Exercise as Prevention

The scientific rationale for exercise in hypertension is largely built on population studies. Cross-sectional studies have been inconsistent, but many find blood pressure to be significantly lower in active individuals than in their sedentary peers. In one survey of 1,700 men, those who had the least estimated energy expenditure had the highest mean blood pressure, while the most active men had the lowest mean. The effect of activity was small (3 mm Hg) but significant, and held for all age groups (16 to 64) in the study (4).

Similar findings have been reported in studies involving young (mean, 26 years) and older (mean, 56 years) runners, whose systolic and diastolic pressures were 6 mm Hg lower than age-matched sedentary controls (5); school-age children, whose fitness scores were inversely related to blood pressure (6); and women (7).

Longitudinal studies provide a larger and more consistent body of research. The recent surgeon general's report, Physical Activity and Health, lists five cohort studies, involving between 5,000 and 41,000 individuals, that found significant inverse associations between exercise and the risk of developing hypertension (8).

One of the most widely cited of these studies followed nearly 15,000 male college alumni for 6 to 10 years and found that those who expended less than 2,000 kcal/week in sports, walking, and stair-climbing had a one-third greater risk of becoming hypertensive than the others (9). Another study (10), involving 6,000 normotensive men and women, aged 20 to 65 at entry, found that patients low in fitness were 50% more likely to develop hypertension over the following 1 to 12 years than those in the high fitness category.

Although most studies have involved men either predominantly or exclusively, it appears that the effect of exercise on hypertension risk is not sex-specific. A study(11) of nearly 42,000 women aged 55 to 69 found risk reductions of 30% and 10% in those who participated in physical activity at high and moderate levels, respectively, over a 2-year period.

The above were prospective observational studies. Only one randomized primary prevention trial involving exercise has been conducted (12). In that study, 201 hypertension-prone individuals were randomly assigned either to a group receiving nutrition and exercise counseling or to a control group. The incidence of hypertension was 54% lower in the intervention group (8.8% vs 19.2%) over a 5-year period. (The multimodal design of this trial made it impossible to assess the contribution of exercise per se to the outcome.)

The Case for Exercise as Treatment

Important as prevention is, physicians may have a more immediate interest in exercise as a therapeutic modality. In its position statement on physical activity, physical fitness, and hypertension (13), the American College of Sports Medicine (ACSM) reviewed 40 studies published prior to 1992 that dealt with the effect of endurance exercise on individuals who had hypertension. The 1,574 individuals enrolled in these studies all had systolic hypertension (over 140 mm Hg), and nearly half had diastolic hypertension (over 90 mm Hg) as well.

Roughly three-fourths of the 40 groups showed significant blood pressure reductions: a mean of 11 mm Hg in systolic pressure (from 153 mm Hg at baseline) and 9 mm Hg in diastolic pressure (from 99 mm Hg). The ACSM concluded that endurance exercise training lowers systolic and diastolic blood pressure, measured in the laboratory or a clinic setting, by approximately 10 mm Hg in most individuals who have mild elevations.

Influence of gender and weight. An earlier meta-analysis (14) of 25 clinical trials looked more closely at patient variables and found that both men and women benefited from endurance training, with the effect significantly greater in women (a mean reduction of 19/14 mm Hg) than in men (7/5 mm Hg). Benefits for heavier persons appeared to be lower, but there was no significant correlation between weight change and blood pressure reduction. Comparable effects have been seen in adolescents, individuals over 60, and those in between (13).

Intensity and duration. Some studies have examined the antihypertensive effects of varying exercise intensities and durations. Generally, it appears that training in the range of 40% to 70% of VO2 max was as effective as, if not more effective than, a more intense regimen (15). Blood pressure reductions typically appeared within 3 months of the start of training, and further reductions did not occur after that. Some studies (14), however, have found that diastolic pressure reductions were related to the duration of the regimen, and one involving older patients (15) found that improvements achieved in the first 3 months of exercise training increased further with an additional 6 months of training. Generally, when exercise was discontinued, blood pressure rose again.

Resistance training. While endurance (aerobic) exercise has been used in most of these studies, some researchers have examined the effect of resistance training. Hypertensive individuals have traditionally been warned away from such activities out of fear that an acute pressor response could threaten a stroke or myocardial infarction. The studies that have been done did not show a deleterious effect, however, and three investigations (16) have documented blood pressure reductions with chronic resistance exercise. One of the studies involved 16 weeks of high-intensity resistance training in a group of normotensive men; another involved 9 weeks of circuit weight training by mildly hypertensive men. The effects were reductions of about 5 mm Hg in resting diastolic blood pressure.

Limitations on the role of exercise. One must keep in mind that even an optimal exercise regimen by itself often fails to normalize participants' blood pressure. Particularly when elevations are more than mild, exercise may not obviate the need for antihypertensive medication. In medicated patients, however, the few studies that have addressed the question suggest that exercise further reduces blood pressure (13,17). In animal subjects, training lowers the amount of antihypertensive drugs needed (18), and clinical experience suggests that the same training effect may apply in humans.

Complementary risk reduction. The rationale for treating hypertension is the reduction of cardiovascular morbidity and mortality. It is important to note that exercise has a positive effect on other cardiovascular risk factors, such as blood lipid levels, body weight, and insulin resistance. Overall, more than 40 clinical studies suggest an inverse relationship between physical activity and the incidence of coronary artery disease (13).

Of particular interest are published studies showing significantly lower all-cause mortality in hypertensive individuals who exercise. In one of the most noteworthy of these clinical studies (19), hypertensive men and women who were fit were found, over an 8-year follow-up period, to have a 60% lower mortality rate than their unfit normotensive peers.

Mechanisms of Efficacy

Neurologic changes. Of the various proposed explanations of the effect of exercise on blood pressure, the most widely accepted ones focus on reductions in sympathetic nervous system tone. It has been reported (20) that exercise training lowers plasma norepinephrine and that the magnitude of the reduction correlates with blood pressure improvement. Another study (21) found that after 10 weeks of endurance training, blood pressure reduction was accompanied by a decrease in sympathetic neural discharge.

Researchers have also reported increases in resting levels of atrial natriuretic factor in well-trained men and a transient increase in this vasodilating hormone when minimally trained subjects exercise (22).

By repeatedly stimulating the release of catecholamines, exercise may decrease the sensitivity of adrenoreceptors, attenuating the blood pressure response to stress. In one study (23), blood pressure elevation in response to cold pressor stimulation was less in well-trained individuals, suggesting that reduced blood pressure lability during non-exercise-related stress may be one of the benefits of exercise training. In another study (24), coronary artery responses to adrenergic agonists and vasoactive intestinal polypeptide were reduced in well-trained dogs.

Effects on other systems. Other, less well-documented explanations for the hypotensive effect of exercise include alterations in insulin metabolism, body composition, and fat distribution (3).

Prescribing Exercise

Patient selection and screening. In clinical practice, exercise should be a central part of blood pressure management in three contexts:

• As part of a prevention program for those at high risk for hypertension (suggested by family history, for example);
• As part of an initial treatment strategy, along with other lifestyle modifications, for patients who have mild (under 160/100 mm Hg) or labile hypertension; and
• As an adjunct to medication for those who have more severe elevations (over 160/105 mm Hg).

An extensive preexercise evaluation including stress testing is not necessary for most patients who do not have established heart disease or severe cardiovascular risk factors (high cholesterol, family history of early coronary artery disease, smoking, obesity, or glucose intolerance).

For patients whose hypertension is shown, over several weeks, to be mild to moderate (pressures under 160/105 mm Hg), I usually suggest a 3-month trial of lifestyle modification before initiating drug therapy. This trial includes, in addition to the exercise prescription, a diet low in salt, alcohol, and (for overweight patients), calories. Also, patients who smoke should be strongly urged to quit.

Exercise guidelines. The basic exercise prescription for all three groups is similar to that recommended by the ACSM (13) to develop and maintain cardiovascular and muscular fitness in healthy adults: at least a half-hour of endurance exercise at 50% to 75% of maximal oxygen uptake (50% to 70% of maximum heart rate) done at least 3 days a week.

Exercise type and progression. The type of aerobic exercise is largely a matter of patient preference. Walking at a 15-minute/mile pace is ideal for many—it requires no equipment or special clothing and fits readily into most patients' schedules. Some prefer jogging, biking, or swimming. Exercise machines such as treadmills, stationary cycles, or cross-country ski devices provide an effective workout for individuals who enjoy exercising at home or at a health club or gym.

Patients who have been sedentary for years may not be able to exercise at the target intensity without a period of gradual adaptation. They should be advised to walk at a comfortable pace at first, without attention to heart rate, for half-hour sessions, increasing the pace as their conditioning improves.

While aerobic activity is the keystone of the exercise program, I also advocate modest resistance exercise (light dumbbells or Nautilus- or Cybex-type exercise machines) as an adjunct for overall fitness. At least one resistance session per week should be done and should focus on upper-body muscles, which are not worked by most aerobic programs.

Medication-Exercise Interactions

A patient whose hypertension is severe or fails to normalize with lifestyle modification alone will most likely need medication. Some antihypertensive drugs can impair the ability to exercise or alter the body's response to exercise (see "Treating Hypertension in Active Patients: Which Agents Work Best With Exercise?" September 1997, page 47). Whatever agent is chosen, it is important to work closely with the patient to monitor his or her response to the combined regimen.

ACE inhibitors. Angiotensin-converting enzyme (ACE) inhibitors are least likely to interact with exercise in a troublesome way, and I generally recommend them as first-line drugs, particularly for patients who work out a good deal.

These drugs are contraindicated, however, in women who are pregnant or who may become pregnant; their use during the second and third trimester may result in severe fetal injury or fetal death. These agents occasionally worsen exercise-induced asthma (25). When diuretics are combined with ACE inhibitors in patients who exercise, the diuretic dose should be reduced to avoid severe hypotension.

Beta-blockers. Beta-blockers can cause significant reductions in heart rate, an effect that must be taken into account in assessing exercise intensity. The exercise prescription for patients taking these drugs is best established by treadmill testing after the dosage is stabilized. Beta-blockers may also cause muscle fatigue and make it more difficult for patients to comply with the exercise regimen.

In the presence of beta-blockers, there is an increased incidence of hyperkalemia (26) with aerobic exercise, and disturbances in heat dissipation during hot-weather activities can occur. Among active patients, these drugs may also mask a hypoglycemic response in diabetic persons and may worsen asthma or trigger or exacerbate exercise-induced asthma. Active patients performing high-intensity or prolonged endurance exercise should not be treated with beta-blockers.

Calcium channel blockers. Patients who take calcium channel blockers may experience orthostatic problems after exercise; however, a cool-down period will prevent orthostasis. These drugs can also produce or worsen esophageal reflux, which may cause difficulties during swimming, for example.

Long-acting calcium channel blockers, especially dihydropyridines, are better choices for active patients than short-acting types, especially for patients who have asthma or heart disease. Short-acting calcium channel blockers have been associated with increased mortality in patients who have heart disease. In addition, verapamil and diltiazem may restrict maximum heart rate.

Diuretics. Electrolyte depletion, a general concern with diuretics, may be exacerbated in patients who perspire a good deal during exercise. Sodium and potassium levels should be monitored more frequently in these individuals. Diuretics should be used cautiously in patients who have diabetes or chronic renal insufficiency.

Compound benefits. The antihypertensive effects of lifestyle modification in combination with pharmacotherapy are additive and may increase over time. Careful tracking of blood pressure, through home monitoring and regular follow-up visits, in patients who exercise regularly may show it is possible to reduce the doses of some medications or, in some cases, to discontinue them altogether.

Encouraging Activity

While even an optimal exercise regimen may not normalize blood pressure, regular, moderate activity can significantly reduce it. Hypertensive patients who have severe cardisvascular risk factors, such as high cholesterol, a family history of early coronary artery disease, or smoking, may need a preexercise evaluation. But physicians can generally recommend moderate endurance and resistance exercise, even for their patients who are taking medication to reduce high blood pressure.

References

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Dr Bove is chief of the cardiology section at the Temple University School of Medicine in Philadelphia. Mr Sherman is a freelance writer in New York City. Dr DiNubile is an orthopedic surgeon in private practice in Havertown, Pennsylvania, specializing in sports medicine and arthroscopy. He is the director of Sports Medicine and Wellness at the Crozer-Keystone Healthplex in Springfield, Pennsylvania; a clinical assistant professor in the department of orthopedic surgery at the University of Pennsylvania in Philadelphia; the orthopedic consultant to the Philadelphia 76ers basketball team and the Pennsylvania Ballet; and a member of the editorial board of The Physician and Sportsmedicine. Address correspondence to Alfred A. Bove, MD, Temple University Medical School, Cardiology Section, 3401 N Broad St, Philadelphia, PA 19140.

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