(Hypertension. 2000;36:171.)
© 2000 American Heart Association, Inc.
Scientific Contributions |
Effects of Exercise and Weight Loss on Mental Stress–Induced Cardiovascular Responses in Individuals With High Blood Pressure
From the Department of Psychiatry and Behavioral Science (A.G., A.S., E.C.D.G., M.A.B., D.T., R.B., J.A.B.) and the Department of Medicine (R.W.), Duke University Medical Center, Durham, NC; the Department of Medicine (A.H.), University of North Carolina, Chapel Hill; and the Department of Psychology (L.C.), University of Colorado, Boulder.
Correspondence to Anastasia Georgiades, PhD, Department of Psychiatry and Behavioral Science, Box 3119, Duke University Medical Center, Durham, NC 27710.
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Abstract |
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Abstract—The purpose of this study was to determine the effects of exercise and weight loss on cardiovascular responses during mental stress in mildly to moderately overweight patients with elevated blood pressure. Ninety-nine men and women with high normal or unmedicated stage 1 to stage 2 hypertension (systolic blood pressure 130 to 179 mm Hg, diastolic blood pressure 85 to 109 mm Hg) underwent a battery of mental stress tests, including simulated public speaking, anger recall interview, mirror trace, and cold pressor, before and after a 6-month treatment program. Subjects were randomly assigned to 1 of 3 treatments: (1) aerobic exercise, (2) weight management combining aerobic exercise with a behavioral weight loss program, or (3) waiting list control group. After 6 months, compared with control subjects, participants in both active treatment groups had lower levels of systolic blood pressure, diastolic blood pressure, total peripheral resistance, and heart rate at rest and during mental stress. Compared with subjects in the control group, subjects in the exercise and weight management groups also had greater resting stroke volume and cardiac output. Diastolic blood pressure was lower for the weight management group than for the exercise-only group during all mental stress tasks. These results demonstrate that exercise, particularly when combined with a weight loss program, can lower both resting and stress-induced blood pressure levels and produce a favorable hemodynamic pattern resembling that targeted for antihypertensive therapy.
Key Words: hypertension, essential • exercise • obesity • stress • hemodynamics
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Introduction |
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Epidemiological studies have shown that increased levels of physical activity reduce the incidence of all-cause mortality and cardiovascular-related deaths.1 Although the mechanisms responsible for this benefit are not fully understood, exercise is known to have favorable effects on such traditional risk factors as elevated blood pressure (BP),2 hyperinsulinemia,3 and hyperlipidemia.4 Recently, a number of biobehavioral risk factors that potentially may be modifiable with exercise have been identified.5 For example, exercise has been shown to reduce depression,6 anxiety,7 and type A behavior.8
An exaggerated cardiovascular response to mental stress is an additional risk factor, which has been shown to be associated with myocardial ischemia9 and is predictive of the future development of hypertension10 11 and coronary heart disease.12 A series of cross-sectional studies have shown that individuals who are more active or physically fit have lower cardiovascular responses to stress.13 Longitudinal studies are less consistent but generally demonstrate that heart rate (HR) and BP levels are attenuated after exercise training in healthy normotensive men and women.14 However, to the best of our knowledge, the effects of exercise on BP stress responses in hypertensive individuals has not been studied. Moreover, because weight loss is associated with lower clinic BP15 but has not been studied in association with mental stress, the effect of exercise, combined with weight loss, on mental stress–induced BP also was examined. This was part of a larger investigation examining the effects of exercise and weight loss on BP.16
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Methods |
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Subjects
Participants were recruited from newspaper, TV, and radio advertisements, referrals from local clinics, and BP screenings at community health fairs and shopping centers. Details of subject recruitment are reported elsewhere.16 Subjects were eligible if they were at least 29 years old, sedentary, and moderately overweight (body mass index 25 to 37 kg/m2) and had a systolic blood pressure (SBP) between 130 and 180 mm Hg and a diastolic blood pressure (DBP) between 85 and 105 mm Hg. Screening BP measurements were obtained by a specially trained technician using a random zero sphygmomanometer with subjects in a sitting position. BP was measured 4 times at 2-minute intervals after an initial rest period of 5 minutes, and the first of these was discarded. Measurements were conducted on 4 separate visits over a 3-week period. In this way, 133 men (40%) and women (60%),
25% of
whom were black, were enrolled in the study.
BP Measurements During Mental Stress
BP was measured using a Suntech 4240 BP monitor (Suntech Medical
Instruments) during a mental stress protocol consisting of a 20-minute
baseline rest period and a series of 4 mental stress tasks,
presented in a counterbalanced order, with a 10-minute rest
period between each task. The tasks consisted of the following: (1) a
public speaking task, in which subjects were asked to give a 3-minute
talk about a current events topic, eg, discussing whether the United
States should risk American lives to be involved in peacekeeping
missions to nations like Bosnia; (2) an anger interview, in which
subjects were given 3 minutes to relate an interpersonal situation that
made them angry during the previous week; (3) mirror image tracing, in
which subjects had 3 minutes to accurately outline a star, viewed in a
mirror, as many times as possible; and (4) cold pressor, in which
subjects placed their right foot in a bucket of ice water (0°C to
4°C) for 1 minute 40 seconds.
To examine whether exercise and weight loss differently affected hemodynamic patterns of stress responses induced by the different stressors, tasks were administered in counterbalanced order. The selection of tasks was based on the type of physiological response that each tends to elicit. Public speaking and anger interview represent 2 active coping tasks that produce cardiovascular responses dominated by increased cardiac output (CO), whereas the mirror trace and cold pressor elicit cardiovascular responses dominated by increased vascular resistance.17
Hemodynamic Measurements
CO and stroke volume (SV) were assessed by use of impedance
cardiography. This noninvasive technique involves recording
changes in thoracic impedance by use of a tetrapolar electrode system,
together with a standard ECG.18 A Minnesota Model 304B
impedance cardiograph was used in conjunction with the standard
tetrapolar band electrode configuration for signal
acquisition.19 Two voltage electrode bands were applied,
one around the base of the neck and one around the thorax at the level
of the xiphoid process. The 2 current electrode bands were applied
around the neck and chest, parallel to the voltage electrodes, with a
constant distance of 4 cm above (neck) and below (chest) the voltage
electrode bands. Impedance signals were recorded and processed with
the use of empirically validated computer software.19 The
Kubicek equation20 was used to compute SV and CO. All
impedance data were based on 30-second samples of continuous data that
were recorded to correspond temporally to the 30-second periods of
cuff deflation associated with BP measurements.
Simultaneous measurement of CO and arterial BP
allowed for the derivation of the total peripheral
resistance (TPR) of the systemic vasculature by using the following
equation: TPR (dyne-s ·
cm-5) =(MAP/CO)x80, in
which mean arterial pressure (MAP)=DBP+(SBP-DBP)/3.
Aerobic Fitness Measurements
Maximal exercise testing was performed by using the Duke–Wake
Forest protocol, in which graded exercise began at 2.0 mph and 0%
grade, and workload was increased at a rate of 1
Met/min.21 BP was obtained at each workload by use
of a Suntech 4240 BP monitor (Suntech Medical Instruments). Expired
gases were collected for determination of peak oxygen consumption (peak
O2) by use of a
metabolic cart (SensorMedics).
Interventions
Exercise Only
Participants in the aerobic exercise-only group participated in
a supervised exercise program in which they exercised 3 or 4 times per
week at a level of 70% to 85% of their initial heart rate
reserve,22 which was determined at the time of the
baseline exercise test. The exercise routine consisted of 10 minutes of
warm-up exercises, 45 minutes of biking and walking (and eventually
jogging), and 10 minutes of cool-down exercises. Subjects were
instructed to maintain their usual diets.
Weight Management
Participants in the weight management group exercised 3 or 4
times per week and followed the identical protocol described above. In
addition, they also participated in a behavioral weight management
program, consisting of 26 weekly 30-minute group meetings of 3 to 5
participants. The program was based on the LEARN manual.23
The goal of the intervention was a weight loss of 1 to 2 pounds per
week brought about by reducing caloric and fat intake through lifestyle
changes. Initial dietary goals were set at 1200 calories for women
and 1500 calories for men, with 15% to 20% of calories coming from
fat.
Waiting List Controls
Participants in the waiting list control group maintained their
usual dietary and exercise/activity habits until the completion of the
6-month evaluation. Subjects were interviewed at monthly intervals to
ensure that patients adhered to these conditions. After the 6-month
period, subjects were free to engage in exercise and to modify their
diets and eating patterns to lose weight if desired.
Statistical Analysis
Baseline differences between treatment groups were assessed by
1-way ANOVA for each cardiovascular variable.
Treatment effects were evaluated by 1-way ANOVAs with posttreatment
measures serving as the dependent variables and treatment group
serving as the between-subject factor. Before each analysis,
outcome measures were residualized on their respective pretreatment
levels to adjust for baseline differences and to increase the precision
of estimates. Separate ANOVAs were estimated for each task on SBP, DBP,
CO, TPR, SV, and HR levels.
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Results |
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Subject Characteristics
Of the 133 subjects initially recruited, 112 patients (84%) completed the study. Because of technical difficulties with the hemodynamic measurements, however, data were not available for 13 participants. Thus, of the 112 patients, 99 (44 in the weight management group, 36 in the exercise-only group, and 19 in the wait list control group) completed all laboratory tasks at both pretreatment and posttreatment assessments and were included in the final analysis. The treatment groups and controls did not differ significantly from each other in age, pretreatment screening BP levels, aerobic fitness, or body composition. Demographic characteristics, including gender and ethnicity, were also similar in the 3 groups (Table 1).
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Effects of Treatment on Fitness Level
Compared with the waiting list control group, both active
treatment groups achieved significant improvements in aerobic fitness.
Posttreatment peak O2 and
treadmill time were greater for both the exercise-only and weight
management groups compared with the control group. The treatment groups
achieved comparable improvements in peak
O2 (Table 2).
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Effects of Treatment on Body Weight
Compared with subjects in the exercise-only group (weight loss
-1.8±0.8 kg) and the control group (weight gain 0.7±1.0 kg),
subjects in the weight management group lost significantly more weight
(-7.8±0.7 kg, P<0.001; Table 2).
Effects of Treatment on Hemodynamic Measurements
Pretreatment Hemodynamics During Rest and Mental Stress
Pretreatment mean levels for SBP, DBP, HR, CO, TPR, and SV during
rest and mental stress are presented in Table 3. The groups were similar in all
pretreatment hemodynamic measurements. Compared with
the mirror trace and cold pressor, anger interview and public speech
elicit an increase in SBP and CO, whereas compared with anger interview
and public speech, the mirror trace and cold pressor elicit larger DBP
and TPR responses (see Table 3).
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Posttreatment Hemodynamics During Rest
After 6 months, there were significant treatment group main
effects at rest. Contrasts revealed that both active treatment groups
had significantly lower resting levels of SBP, DBP, HR and TPR than did
the control group (P<0.01 for all). In addition, both
active treatment groups had significantly higher levels of SV and CO
than did the control group (P<0.01 for all). Comparisons
between the treatment groups showed that the weight management group
had significantly lower resting DBP and TPR levels than did the
exercise-only group (see Figure)
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P<0.01 for
exercise-only group compared with control group; and
P<0.01 for weight management group compared with
exercise-only group.
Posttreatment Hemodynamics During Mental
Stress
There also were significant treatment group main effects during
mental stress. Compared with the control group, both active treatment
groups had significantly lower SBP levels during all stressors
(P<0.01 for all). In addition, compared with the control
group, both intervention groups had significantly lower HR and higher
SV during every task (P<0.01 for all). During the mirror
trace task, both groups had significantly lower levels of SBP, DBP,
TPR, and HR and higher levels of SV and CO than did the control group
(P<0.01 for all). The active treatment groups did not
differ from each other in SBP or CO levels during any of the tasks;
however, compared with the exercise-only group and the control group,
the weight management group had significantly lower DBP levels during
all tasks (see Figure).
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Discussion |
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Results from the present study show that in mild to moderate obese individuals with elevated BP, exercise training alone and in combination with a behavioral weight loss program can lower BP and produce favorable hemodynamic alternations, both at rest and during mental stress. It has previously been established that aerobic training can lower resting BP levels.24 However, there are only a few controlled prospective intervention trials investigating the association between exercise and cardiovascular responses during mental stress, and of those, no previous study has investigated the effect of exercise in hypertensive individuals or on changes in hemodynamic function during mental stress. Moreover, despite evidence that weight loss is associated with reduced resting BP,15 to the best of our knowledge, this is the first study to demonstrate that a weight loss intervention is associated with a reduction in BP during mental stress.
In the present study, compared with the control group, both the exercise-only and the weight management group had significantly lower SBP and DBP levels during mental stress after treatment. Previous studies conducted primarily with normotensive nonobese subjects have shown that exercise can attenuate HR and BP responsivity to mental stress.25 26 However, because the individuals in those studies were either college students or healthy younger men and women, the clinical importance of the findings was not established.
On the other hand, compared with normotensive control individuals, hypertensive individuals have been found to exhibit larger cardiovascular responses to mental stress.27 Therefore, reductions in BP levels during mental stress may be more clinically meaningful among individuals with mild hypertension than among healthy individuals with normal BP.
Although the clinical significance of BP during mental stress testing is unclear, there are several studies showing that cardiovascular responses during mental stress are better predictors of future hypertension10 11 and target organ damage28 than are resting BP measurements. Because BP levels are highly influenced by factors such as daily activities and mood,29 it has been hypothesized that cardiovascular responses during behavioral challenge or daily life may be better predictors of future BP levels and target organ damage than responses during resting conditions. Indeed, there is accumulating evidence that end-organ damage can progress despite control of resting BP levels30 31 and that BP levels during mental stress are more closely associated with left ventricular mass than are resting BP levels.32
Beneficial changes in the hemodynamic pattern resulting from treatment were also observed. The posttreatment hemodynamic alternations were characterized by decreased TPR and increased CO within both active treatment groups compared with the control group during the resting condition and during mental stress. Previous research has demonstrated that aerobic exercise training increases resting SV and reduces resting HR.33 Because CO is determined by SV and HR, the increased CO seen in the 2 active treatment groups was mediated by increased SV, because HR levels were significantly lower during rest and mental stress testing. Individuals in the exercise-only and weight management groups also had lower TPR after treatment than did subjects in the control group. The pretreatment hemodynamic pattern of subjects in the present study was characterized by elevated TPR and normal CO, a hemodynamic profile typically seen in patients with established hypertension.34 Because there were no differences in the hemodynamic patterns between the 2 active treatment groups, it is possible that aerobic exercise, the common feature of both interventions, was largely responsible for the increased CO and SV and lowered TPR relative to the control group. These hemodynamic changes are similar to those achieved with pharmacological antihypertensive therapy.35 It should be noted that the participants in the present study were highly motivated and that the program was supervised. It remains to be seen whether the same success in treatment effects can be achieved with an unsupervised exercise/diet intervention or among individuals who are less motivated to participate in such a treatment.
Antihypertensive medications strive to have a long-term beneficial effect on the hemodynamic pattern by lowering BP and reducing TPR.36 The present study shows that exercise and weight loss can reduce BP levels and change the hemodynamic pattern into a more favorable one, similar to that achieved with antihypertensive therapy.35 These data further suggest that exercise and weight loss are effective nonpharmacological treatments for elevated BP in mild to moderate obese individuals, consistently lowering BP and TPR during rest and during mental stress.
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Acknowledgments |
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This research was supported by grants HL-49572 and HL-59672 from the National Institutes of Health. The authors wish to acknowledge the assistance of Dr Mohan Chilukuri for performing the physical examinations; Julie Opitek, PhD, Karen Mallow, MS, and Kelli Dominick, MS, for performing the exercise testing and training; Jennifer Norten, PhD, for assisting with the weight management groups; Connie Bales, PhD, for her nutritional advice; and the nutrition, dietary, and research staff of the General Clinical Research Center and the M01-RR-30 General Research Centers Program, National Center for Research Resources, National Institutes of Health.
Received February 23, 2000; first decision March 8, 2000; accepted March 13, 2000.
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