Reduction of coronary atherosclerosis by moderate conditioning exercise in monkeys on an atherogenic diet

Physical fitness as a predictor of mortality among healthy, middle-aged Norwegian men

BACKGROUND

Despite many studies suggesting that poor physical fitness is an independent risk factor for death from cardiovascular causes, the matter has remained controversial. We studied this question in a 16-year follow-up investigation of Norwegian men that began in 1972.

METHODS

Our study included 1960 healthy men 40 to 59 years of age (84 percent of those invited to participate). Conventional coronary risk factors and physical fitness were assessed at base line, with physical fitness measured as the total work performed on a bicycle ergometer during a symptom-limited exercise-tolerance test.

RESULTS

After an average follow-up time of 16 years, 271 men had died, 53 percent of them from cardiovascular disease. The relative risk of death from any cause in fitness quartile 4 (highest) as compared with quartile 1 (lowest) was 0.54 (95 percent confidence interval, 0.32 to 0.89; P = 0.015) after adjustment for age, smoking status, serum lipids, blood pressure, resting heart rate, vital capacity, body-mass index, level of physical activity, and glucose tolerance. Total mortality was similar among the subjects in fitness quartiles 1, 2, and 3 when the data were adjusted for these same variables. The adjusted relative risk of death from cardiovascular causes in fitness quartile 4 as compared with quartile 1 was 0.41 (95 percent confidence interval, 0.20 to 0.84; P = 0.013). The corresponding relative risks for quartiles 3 and 2 (as compared with quartile 1) were 0.45 (95 percent confidence interval, 0.22 to 0.92; P = 0.026) and 0.59 (95 percent confidence interval, 0.28 to 1.22; P = 0.15), respectively.

CONCLUSIONS

Physical fitness appears to be a graded, independent, long-term predictor of mortality from cardiovascular causes in healthy, middle-aged men. A high level of fitness was also associated with lower mortality from any cause.

Risk factors for coronary heart disease: synthesis of a new hypothesis through adaptation

A risk factor is a characteristic which is associated with a greater than average probability of developing coronary disease. Raised serum cholesterol and hypertension are two such factors. Intervention studies conducted to confirm the risk factor hypothesis have shown that reduction of serum cholesterol and essential hypertension may be associated with a small decreased CHD incidence, however there were almost as many deaths due to coronary disease in the intervention groups as in the control groups. These findings suggest that our approach to risk factor intervention may be a misguided attempt which needs modification. It is possible that the major risk factors develop in an attempt of our body to adapt to environmental factors such as increased intake of salt, saturated fat and cholesterol, physical inactivity, increased intake of calories and obesity and stress. Smoking may be the result of social changes. Since the body has to modify its metabolic mechanism depending upon the factor to which it adapts, development of hyperlipidemia and hypertension may be protective mechanisms of the body which it has developed while fighting against environmental factors. Reduction of major risk factors by drug therapy may mean that we are trying to prevent the body, fighting environmental factors. Thus our approach to control of the major risk factors should be to treat the causative environmental factors or alter the lifestyle.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise and the heart. Good, benign, or evil?

The risks and benefits of regular aerobic exercise have been studied extensively. Because of the potential risks, we believe that sedentary persons over age 40 who have cardiac risk factors, as well as patients with coronary artery disease (CAD), should have a complete physical examination and probably an exercise electrocardiogram before starting a vigorous exercise program. In general, however, regular exercise has proven to be extra-ordinarily safe and the theoretical and proven benefits appear to greatly outweigh the risks in most people, including those with CAD, those with severe left ventricular dysfunction, and the elderly.

Exercise as a coronary protective factor

Exercise has multiple beneficial actions, both in normal subjects and in patients with coronary artery disease, which can be cardioprotective. Apart from reducing known risk factors and protecting against their deleterious effects, exercise also reduces the risk of coronary artery disease by increasing cardiovascular fitness. The exact contribution of each of these mechanisms in reducing coronary artery disease morbidity and mortality is unclear. Although fitness may be desirable, much of the cardioprotection can be achieved through increased leisure time and recreational physical activity. The risk-benefit ratio is very much in favor of moderate intensity exercise. Even in the absence of a controlled trial, the available evidence suggests that efforts to encourage physical activity are justified.

Use of serum lipid and apolipoprotein concentrations to predict extent of diet-induced atherosclerotic lesions in aortas and coronary arteries and to demonstrate regression of lesions in individual rhesus monkeys

In most studies, the assessment of lesion "regression" is based on comparisons of group means between the "progression" and regression groups. This comparison depends on the assumption that the extent and distribution of lesions produced by the end of the lesion-induction period in the regression animals are equal to those observed in the progression group. To determine whether significant regression of lesions occurs in an individual regression animal, it is necessary to obtain a measure of the lesions produced in these animals at the end of the lesion-induction period. We achieved this goal by developing models using multiple stepwise regression analysis that related steady-state serum cholesterol and apolipoprotein B and A-I concentrations measured during a lesion-induction period in 27 rhesus monkeys fed an atherogenic high-saturated-fat/high-cholesterol diet for 2 years. The models were developed to estimate the percent of intimal surface with lesions, the esterified cholesterol content (micrograms/cm2) for the artery segments, and three histomorphometric measures (mean intimal thickness, mean maximal intimal thickness, and mean percent stenosis) for the coronary arteries. In these models, multiple R2 ranged from 0.42 to 0.74 for the aortas and peripheral arteries, indicating that approximately one half to three fourths of the variance in lesions was accounted for. For the three histomorphometric measures in coronary arteries, however, the multiple R2 was 0.27 or 0.28, indicating that only approximately one fourth of the variance in lesions was accounted for.(ABSTRACT TRUNCATED AT 250 WORDS)

An applied model for the evaluation of multiple physiological stressors

In everyday life, a human is likely to be exposed to the combined effects of a number of different stressors simultaneously. Consequently, if an applied model is to ultimately provide the best 'fit' between the modeling and modeled phenomena, it must be able to accommodate the evaluation of multiple stressors. Therefore, a multidimensional, primate model is described that can fully accommodate a large number of conceivably stressful, real life scenarios that may be encountered by civilian or military workers. A number of physiological measurements were made in female rhesus monkeys in order to validate the model against previous reports. These evaluations were further expanded to include the experimental perturbation of physical work (exercise). Physiological profiles during activity were extended with the incorporation of radio telemetry. In conclusion, this model allows maximal extrapolation of the potential deleterious or ergogenic effects on systemic physiological function under conditions of realistic operational demands and environments.

Cardiovascular rehabilitation: status, 1990

Cardiovascular rehabilitation is defined as the process of development and maintenance of a desirable level of physical, social, and psychologic functioning after the onset of a cardiovascular illness. Patient education, counseling, nutritional guidance, and exercise training play prominent roles in the process of rehabilitation. Benefits from cardiac rehabilitation include improved exercise capacity and decreased symptoms of angina pectoris, dyspnea, claudication, and fatigue. Recent pooled data regarding exercise training after myocardial infarction demonstrated a 20 to 25% reduction in mortality and major cardiac events. Exercise training may result in an improvement in systemic oxygen transport, a reduction in the myocardial oxygen requirement for a given amount of external work, and a decrease in the extent of myocardial ischemia during physical activity. The efficacy of modification of risk factors in reducing the progression of coronary artery disease and future morbidity and mortality has been established. Herein we review the history, current practice and results, and future challenges of cardiovascular rehabilitation.

The domestic goat: a useful model to determine effects of diet and exercise on cholesterol accumulation in the body

1. Young goats were used to study factors contributing to atherosclerosis. 2. Cholesterol in egg yolk affected plasma cholesterol concentration more than did a similar amount of crystalline cholesterol in the diet. 3. Goats fed high fat diets developed fatty lesions in their aortas. 4. Cholesterol concentration in low-density lipoprotein was greatest in goats fed restricted-calorie diets without exercise, but least in goats fed liberally and exercised. 5. Cholesterol concentration in liver and fat deposition in aorta were greatest in the restricted-calorie, no exercise regime.

Usefulness of fish oil supplements in preventing clinical evidence of restenosis after percutaneous transluminal coronary angioplasty

This study assesses the effect of dietary supplements with high dose omega-3 fatty acid (N3FA) on the frequency of clinical restenosis during the 6 months after successful percutaneous transluminal coronary angioplasty (PTCA). One hundred ninety-four patients (214 significant coronary narrowings) were randomized after successful PTCA to receive conventional medical therapy or to an identical regimen supplemented by high dose N3FA (4.5 g/day). Enrollment required angina pectoris and successful dilatation of all significant coronary narrowings. The subjects were randomly assigned to either no N3FA (control, n = 99) or N3FA supplementation (n = 95). After a 1-week trial period, 11 (group 2) declined further treatment because of side effects. The remaining 84 subjects (group 1) continued N3FA throughout the 6-month period. Monthly clinical follow-up was obtained in all patients. Ninety-two percent of patients had cardiac testing for evaluation of recurrent ischemia. Except for a greater percentage of women in the group refusing N3FA supplementation (group 2), the 3 groups were similar in demographic data, medical history, dietary habits, history of previous PTCA and angiographic characteristics. Of the 194 subjects, 56 had clinical restenosis (45 by cardiac catheterization, 8 by exercise testing and 3 by symptoms alone [refused further clinical testing]). Reocclusion rates were: group 1 19%, group 2 46%, and control 35%. Analysis both in accordance with the principle of intention to treat and for subjects who actually received N3FA revealed a significant effect of N3FA on preventing clinical restenosis (p less than 0.04 and p = 0.008, respectively). These data suggest that high dose N3FA supplements reduce the clinical restenosis rate after successful PTCA.

Atherosclerosis research in cynomolgus monkeys (Macaca fascicularis)

This is a review of the utilization of cynomolgus monkeys (Macaca fascicularis) in atherosclerosis research. Naturally occurring and experimentally induced atherosclerosis progression and regression studies are described. This species has been utilized as an animal model to study the effects of immunologic injury, aging, exercise, and drug intervention on atherosclerotic lesions. Cynomolgus macaque atherosclerosis induced by feeding cholesterol is a good model of human atherosclerosis because of similar gender-related differences in susceptibility to coronary artery atherosclerosis, a relatively high incidence of myocardial infarction, and characterized psychosocial factors that influence the development of atherosclerosis.

Exercise, cardiovascular disease and blood pressure

The "chronic" effect of exercise on blood pressure has been controversial and the debate has been confused by a large number of studies with inadequate methodology. Recent consistent findings in epidemiological, experimental and longitudinal intervention studies have suggested that a true antihypertensive effect which is independent of confounding effects of sodium intake, weight, etc. is more likely than not. Unlike some other measures of lowering blood pressure such as sodium restriction, alcohol moderation and some drugs, regular exercise is associated with beneficial effects on several risk factors and probably has an independent effect on cardiovascular mortality. The magnitude of the effect in previously sedentary subjects is greater than that of dietary measures which lower blood pressure except for weight reduction in the obese. Long-term effects on blood pressure are supported by evidence of a favourable influence on left ventricular hypertrophy. The mechanisms involved in the antihypertensive effect of exercise are unclear, but sympathetic withdrawal is one factor involved. Present evidence appears sufficient to include regular exercise amongst the useful therapies for hypertension.

Reversal of atherosis and sclerosis. The two components of atherosclerosis

In 1904, Marchand recognized the consistent association of fatty degeneration and vessel stiffening and introduced the term "atherosclerosis" to indicate this combination. Current research is focused principally on the lipid component, but there is evidence that both aspects are reversible. Atheromatous lipids add significantly to the volume of lesions and thus contribute to vascular obstruction and end-organ damage. Reversal of atherosis has been observed in all the major species used in atherosclerosis research; rabbits, swine, dogs, chicks, pigeons, and subhuman primates. Direct evidence for reversal in humans is based on angiographic trials and is less extensive. One femoral artery and one coronary artery trial indicate that the lesions can be stabilized. CLAS, the largest angiographic trial to date, indicates that coronary lesion reversal is possible. Clinical effects of sclerosis are more subtle, and there is little evidence that sclerosis alone leads to end-organ damage. However, it should be noted that atherosclerotic lesions producing end-organ damage invariably have a major fibrous component. Sclerotic vessels have reduced systolic expansion and abnormally rapid pulse wave propagation, which can be measured noninvasively. Primate studies indicate that sclerosis is induced by hypercholesterolemic diets and is reversible when these diets are withdrawn. Changes in sclerosis may be another useful indicator of the formation and reversal of lesions and may involve changes in EDRF. Future studies of atherosclerosis reversal should use a combination of measures to evaluate both atherosis and sclerosis.

Effects of exercise training on biochemical and biomechanical properties of rat aorta

The authors studied the effect of prolonged physical exercise on the mechanical properties of rat aorta in relation to the amounts and qualities of arterial connective tissue fibrous proteins. Twelve male rats were divided into two groups: 6 sedentary rats (S) and 6 training rats (T), which were forced to swim from nine weeks to twenty-five weeks of age. The ultimate tensile stress and the ultimate tensile extension ratio of ring specimens at the descending thoracic aorta were larger in T than in S (192.3 +/- 47.9 g/mm2, mean +/- SD, vs 147.8 +/- 26.0, p less than 0.05; 3.52 +/- 0.13 vs 3.18 +/- 0.27, p less than 0.05; respectively). The elasticity parameter, calculated by fitting stress-strain curves to exponential function in the stress level of 0-20 g/mm2, was lower in T than in S (1.79 +/- 0.15 vs 2.13 +/- 0.24, p less than 0.01). The contents of elastin (alkali-insoluble elastin preparation) and collagen were higher in T than in S (0.44 +/- 0.11 g/g dry aorta vs 0.30 +/- 0.06, p less than 0.05; 0.15 +/- 0.04 g/g dry aorta vs 0.11 +/- 0.04, NS, respectively). Although the aortic calcium content did not significantly change in the training rats (T 1.17 +/- 0.23 mg/g dry aorta, S 0.95 +/- 0.34), the content of calcium in elastin was lower in T than in S (1.75 +/- 0.51 mg/g dry elastin vs 2.63 +/- 1.00, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Physical fitness as a predictor of cardiovascular mortality in asymptomatic North American men. The Lipid Research Clinics Mortality Follow-up Study

Limited data are available on the relation between physical fitness and mortality from cardiovascular disease. We examined this question in a study of 4276 men, 30 to 69 years of age, whom we followed for an average of 8.5 years. Examinations at base line included assessment of conventional coronary risk factors and treadmill exercise testing. The heart rate during submaximal exercise (stage 2 of the exercise test) and the duration of exercise were used as measures of physical fitness. Men with incomplete data (n = 308) or who were using cardiovascular drugs (n = 213) were excluded from the analysis. Men who had clinical evidence of cardiovascular disease at base line (n = 649) were analyzed separately. Forty-five deaths from cardiovascular causes occurred among the remaining 3106 men. A lower level of physical fitness was associated with a higher risk of death from cardiovascular and coronary heart disease, after adjustment for age and cardiovascular risk factors. The relative risk of death from cardiovascular causes was 2.7 (95 percent confidence interval, 1.4 to 5.1; P = 0.003) for healthy men with an increment of 35 beats per minute in the heart rate during stage 2, and 3.0 (95 percent confidence interval, 1.6 to 5.5; P = 0.0004) for those with a decrement of 4.4 minutes in the exercise time spent on the treadmill. The corresponding values for death from coronary heart disease were 3.2 (95 percent confidence interval, 1.5 to 6.7; P = 0.003) and 2.8 (95 percent confidence interval, 1.3 to 6.1; P = 0.007), respectively. We conclude that a lower level of physical fitness is associated with a higher risk of death from coronary heart disease and cardiovascular disease in clinically healthy men, independent of conventional coronary risk factors.

Low-fat diet and regular, supervised physical exercise in patients with symptomatic coronary artery disease: reduction of stress-induced myocardial ischemia

The effects of physical exercise and normalization of serum lipoproteins on stress-induced myocardial ischemia were studied in 18 patients with coronary artery disease, stable angina pectoris, and mild hypercholesterolemia (total serum cholesterol 242 +/- 32 mg/dl). These patients underwent a combined regimen of low-fat/low-cholesterol diet and regular, supervised physical exercise at high intensity for 12 months. At 1 year serum lipoproteins has been lowered to ideal levels (serum cholesterol 202 +/- 31 mg/dl, low-density lipoproteins 130 +/- 30 mg/dl, very low-density lipoproteins 22 +/- 15 mg/dl, serum triglycerides 105 [69 to 304] mg/dl) and physical work capacity was improved by 21% (p less than .01). No significant effect was noted on high-density lipoproteins, probably as a result of the low-fat/high-carbohydrate diet. Stress-induced myocardial ischemia, as assessed by thallium-201 scintigraphy, was decreased by 54% (p less than .05) despite higher myocardial oxygen consumption. Eighteen patients matched for age and severity of coronary artery disease served as a control group and "usual medical care" was rendered by their private physicians. No significant changes with respect to serum lipoproteins, physical work capacity, maximal rate-pressure product, or stress-induced myocardial ischemia were observed in this group. These data indicate that regular physical exercise at high intensity, lowered body weight, and normalization of serum lipoproteins may alleviate compromised myocardial perfusion during stress.

Inhibition of coronary atherosclerosis by propranolol in behaviorally predisposed monkeys fed an atherogenic diet

We studied the effect of propranolol on the diet-induced coronary artery atherosclerosis (CAA) in 30 adult male cynomolgus monkeys living in social groupings of five animals each. Animals in the "treated" segment (n = 15) consumed propranolol, which was mixed into an atherogenic diet. Animals in the "untreated" group (n = 15) consumed only the atherogenic diet. Finally, the social groupings were subjected to disruption through monthly redistribution of monkeys among the groups within each treatment segment. The experiment lasted 26 months, following which all animals underwent autopsy during which the coronary arteries were evaluated for atherosclerosis. Regarding atherosclerosis, we observed a significant interaction between social status and experimental condition (p less than .03). Socially dominant animals had (as in previous studies) significantly exacerbated CAA, but only in the untreated segment; the effect of social dominance on CAA was abolished by long-term administration of propranolol. The antiatherogenic effect of propranolol on dominant animals was independent of the influences of serum lipid concentrations, blood pressure, and resting heart rate. We conclude that treatment with beta-adrenergic-blocking agents may confer a degree of protection against CAA among individuals behaviorally predisposed to coronary heart disease.

Promotion and regression of atherosclerosis in vervet monkeys by diets realistic for westernized people

We have described and measured aortic and arterial atherosclerosis in adult female Vervet monkeys (n = 61) after application of dietary treatments for 47 months. The diets were compounded entirely of normal food items for westernized people, with no extra cholesterol added. A 'Western' diet (WD), known to induce hypercholesterolaemia, was found to be atherogenic in aortas and some arteries. A more 'prudent' diet (PD) induced much less lipid infiltration into aortic intimas and was not associated with serious atherosclerotic changes. However, when this PD was used as a treatment for 27 months, following 20 months of nutrition by the WD, minimal regression of cholesterol crystals and non-lipid components of atherosclerotic plaque was detected. There was no significant coronary artery or myocardial disease in these adult females after 47 months of feeding on the WD whereas males do develop coronary atherosclerosis and myocardial fibrosis. For this model the PD would be more effective in preventing atherosclerosis than treating advanced lesions. We believe this is the first time that the pathology of atherosclerosis promoted by realistic diets has been modelled in adult females of this species.

Diabetes, insulin and exercise

The metabolic and hormonal adaptations to single exercise sessions and to exercise training in normal man and in patients with insulin-dependent as well as non-insulin-dependent diabetes mellitus are reviewed. In insulin-dependent (type I) diabetes good metabolic control is best obtained by a regular pattern of life which will lead to a fairly constant demand for insulin from day to day. Exercise is by nature a perturbation that makes treatment of diabetes difficult: Muscle contractions per se tend to decrease the plasma glucose concentration whereas the exercise-induced response of the so-called counter-regulatory hormones tend to increase plasma glucose by increasing hepatic glucose production and adipose tissue lipolysis. If the pre-exercise plasma insulin level is high, hypoglycaemia may develop during exercise whereas hyperglycaemia and ketosis may develop if pre-exercise plasma insulin levels are low. Physical activity is often difficult to carry out on a precise schedule and the exercise-induced changes in demand for insulin and calories vary according to the intensity and duration of exercise, time of day, and differ within and between individuals. Thus, physical training can not be recommended as a means of improving metabolic control in insulin-dependent diabetes. However, our present knowledge and technology allows the well-informed and cooperative patient to exercise and even to reach the elite level. To achieve this, pre-exercise metabolic control should be optimal and knowledge of the patient's reaction to exercise is desirable, which necessitates frequent self-monitoring of plasma glucose. It may often be necessary to diminish the insulin dose before exercise, and/or to ingest additional carbohydrate during or after exercise. In non-insulin-dependent (type II) diabetes, exercise is associated with less risk of metabolic derangement, and in genetically disposed individuals physical training may prevent development of overt diabetes possibly by diminishing the strain on the pancreatic beta cell. The latter, however, is only achieved if exercise is not accompanied by increased caloric intake. Whether physical training in diabetes can reduce cardiovascular morbidity and mortality is at present unknown, but training has in diabetic patients been shown to lessen some risk factors for development of arteriosclerosis. However, training of diabetics (especially in the less well-regulated patient) may not lessen coronary risk factors to the same extent as in healthy subjects.

Exercise: a risk for sudden death in patients with coronary heart disease

Although sudden arrhythmic death is usually unrelated to exertion, there is more than anecdotal evidence that strenuous exercise in patients with coronary heart disease carries an additional risk for sudden death. When cardiac arrest has been observed after exercise stress testing or within seconds after collapse associated with exertion, ventricular fibrillation has usually been present and has responded to the prompt application of a defibrillatory shock. Exertion-related cardiac arrest is typically a "primary" arrhythmic event not due to acute myocardial infarction. As estimated here, the additional risk of exercise for cardiac arrest may be more than 100-fold during or after a few minutes of vigorous exertion.

Atherosclerosis: an insulin-dependent disease?

Evidence is reviewed that dietary habits in industrially developed countries, especially an increased frequency of ingestion of foods of high energy density, may contribute to excessive hepatic cholesterol synthesis and to a preponderance of lipogenic versus lipolytic effects on the arterial intima, thereby favoring the formation and progression of atheroma. These effects are mediated by the rise and fall of circulating insulin levels. The evidence is suggestive of the possibility that frequent and prolonged exposure of the arterial wall to high circulating levels of insulin may favor the development of atherosclerotic lesions. Research on diet-atherosclerosis relationships should take into account not only overall diet composition but individual meal composition and size and their effects on serum insulin levels, as well as meal spacing and the relative durations of absorptive and postabsorptive periods during the 24-hour daily cycle.

Nonhuman primate models of atherosclerosis: potential for the study of diabetes mellitus and hyperinsulinemia

Nonhuman primates have been used for many years to investigate the pathogenesis and progression of atherosclerosis. The use of these animal models has resulted in a better understanding of the risk factors associated with atherosclerosis. Nonhuman primates that have consumed an atherogenic diet for several years develop lesions that are comparable to those found in human beings. Diabetes, both spontaneous and chemically induced, has been described in a number of nonhuman primate species. These diabetic models may be used to understand the accelerated progression and vascular complications of atherosclerosis in diabetic human beings.

Exercise and the primary prevention of cardiovascular disease

Longitudinal population studies have consistently demonstrated an association between sedentary lifestyles and the incidence of coronary artery disease (CAD). Diverse lines of evidence from clinical and experimental studies further implicate physical inactivity as an important risk factor for CAD. The relation between physical inactivity and CAD appears to be curvilinear and independent of other major risk factors, but of lower magnitude. Several training-induced physiologic adaptations offer plausible mechanisms for the protective effects of physical activity. Extrapolation from available data indicates that exercise must be habitual, vigorous and continuous to provide protection from CAD. However, the observed association between inactivity and CAD could represent several hypotheses other than cause and effect. The need for an appropriately designed clinical trial is apparent, but such an endeavor is not feasible at present. Until more rigorous scientific data are available, judgment on the use of exercise in prevention of CAD must necessarily be based on the accumulation of evidence supporting the role of physical activity. The rationale for exercise in preventing the occurrence of CAD is reviewed.

Proximal coronary vasomotor reactivity after exercise training in dogs

The effects of exercise on large coronary vasoreactivity were determined in eight dogs trained by treadmill running for 8 weeks. Six nontrained dogs comprised the control group. The trained group showed a significant reduction in heart rate during graded submaximal exercise testing when compared with the controls, and resting plasma levels of norepinephrine (nontrained group, 331 +/- 99 pg/ml; trained group, 142 +/- 30 pg/ml; p less than .05) and epinephrine (nontrained, 424 +/- 105; trained, 258 +/- 45 pg/ml; p less than .05) were reduced significantly in the trained group. Epicardial coronary responses to intracoronary infusion of serotonin and phenylephrine were evaluated by quantitative coronary angiography, and myocardial blood flow was measured with 15 microns radioactive microspheres. Left ventricular/body weight ratio was similar in the trained (4.81 +/- 0.24 g/kg) and nontrained groups (4.79 +/- 0.17), and no differences were noted in resting myocardial oxygen consumption or coronary arteriovenous oxygen difference. The constriction of the proximal left anterior descending artery (LAD) in response to serotonin infusion was not different in the two groups, but the LAD and circumflex artery constrictor responses to phenylephrine were attenuated in the trained when compared with the nontrained dogs. The data indicate that endurance exercise diminishes the large epicardial coronary vasoconstrictor response to alpha-adrenergic stimulation, but not to serotonin. The blunted constrictor response in the trained animals suggests that exercise may be useful in reducing epicardial coronary vasoconstriction, which is thought to be important in some patients with coronary artery disease.

Physical activity levels and coronary heart disease. Analysis of epidemiologic and supporting studies

Coronary heart disease, the primary health problem in western life, is caused by the interaction of multiple factors. Absolute proof of the contributing role of physical inactivity is not possible owing to the complexity of the CHD problem and the infeasibility of a definitive clinical trial because of logistical and economic constraints. Despite limitations, existing epidemiologic studies strongly suggest, but fall short of proving, the concept that habitual physical exercise offers partial protection against primary or secondary events of CHD and associated mortality. However, experimental data support this hypothesis and provide evidence of possible mechanisms responsible for the protection. The available epidemiologic data also suggest that physical inactivity is probably not as potent an individual risk factor as elevated serum cholesterol levels, hypertension, and cigarette smoking, and that the protective effects of exercise may be overwhelmed by high levels of these major risk factors. On the other hand, there is some evidence that exercise may attenuate other risk factors both directly and through associated weight reduction. Epidemiologic studies also suggest a dose response relationship between physical activity and rates of CHD. About 2000 kcal per week of moderate intensity, dynamic, endurance-type of exercise (such as walking or jogging about 20 miles per week) or at least one hour of intermittent hard physical labor are required to obtain the optimal effect of exercise on coronary heart disease rates. Experimental studies suggest that this amount of exercise should provide sufficient stimulus to favorably alter blood HDL cholesterol levels and perhaps other CHD risk factors, especially if there is an accompanying reduction in weight. Possible mechanisms for the protective effects of exercise against CHD are illustrated in Figure 1. Insistence on final experimental proof prior to prudent medical practice or public health policy on physical inactivity or other coronary risk factors indicates a lack of understanding of the nature of scientific proof and evidence required for health actions.(ABSTRACT TRUNCATED AT 400 WORDS)

The effectiveness of a low lipid diet and exercise in the management of coronary artery disease

To evaluate the effects of a high complex carbohydrate, low lipid diet on the management of coronary artery disease, we reviewed data on 32 patients, who had participated in a diet and exercise program, and compared the results with 40 patients who had been managed only with exercise. After a follow-up period of 10 to 16 weeks the patients on the diet-exercise program showed significant reduction in body weight (-6 +/- 2 kg mean +/- standard deviation), serum cholesterol (-43 +/- 41 mg/dl), and triglycerides (-51 +/- 70 mg/dl), while patients who were managed only with exercise had no significant changes in weight or serum lipids. Both the diet-exercise and the exercise groups showed significant improvement in working capacity and reduction in resting systolic blood pressure. Patients on the diet-exercise program had significantly less angina (21.9%) occurring on the exercise test after the program compared to before, even though the same double product was reached. Multiple logistic regression analysis of the data for patients with angina on the exercise test demonstrated that the only significant (p = 0.004) contributor for reduction in angina was the dietary intervention. Beta-blocking drugs did not affect the results. Although randomized controlled trials must be run in order to ascertain the significance of this finding, this study strongly suggests that a low lipid, high carbohydrate diet is a useful addition to exercise in the management of patients with coronary disease.

Retarding effect of lowered heart rate on coronary atherosclerosis

The role of heart rate in the development of coronary atherosclerosis was assessed in adult male cynomolgus monkeys (Macaca fascicularis). Heart rate was lowered in six animals by surgical ablation of the sinoatrial node. A sham procedure, which included all of the surgical steps except for sinoatrial node ablation, was carried out in eight animals. All of the monkeys were fed an atherogenic high cholesterol diet for 6 months, and heart rates were monitored repeatedly by telemetry during 24-hour test periods. Coronary atherosclerosis in animals with postoperative heart rates less than the preoperative mean for all of the animals that underwent surgery was less than half that of animals with heart rates above the mean or of diet-fed control animals not subjected to surgery. Groups did not differ in blood pressure, serum lipids, or body weight. These results suggest that heart rate in itself may contribute to the mechanisms by which behavioral patterns and physical training influence coronary artery disease.

The effects of exercise and a moderate hypercholesterolemic diet on plasma and hepatic lipoproteins in the rat

Exercise generally has been found to produce beneficial effects on plasma lipid and lipoprotein profiles, but the mechanisms involved and possible dietary interactions have not been well defined. Weanling male Fischer 344 rats were assigned to three groups: normocholesterolemic diet sedentary (NS), hypercholesterolemic diet sedentary (HS), and hypercholesterolemic diet exercised (HE). Exercise consisted of treadmill running at 1.2 to 1.4 km/h at a 9% grade, six days weekly, for a 10-week experimental period. Lipoproteins from plasma and from a recirculating in situ liver perfusion system were then isolated and analyzed. The values of several parameters for HE tended to fall intermediate between HS and NS. Final total plasma cholesterol and liver cholesterol concentrations were significantly different among all three groups (HS greater than HE greater than NS). Plasma HDL-cholesterol and phospholipids and perfusate HDL-cholesterol production rate per gram liver were all significantly lower in HS v NS, with HE lying in between. Plasma HDL protein was lower in HS than in both other groups. Plasma total triglyceride levels were significantly lowered by exercise, but neither plasma nor perfusate VLDL triglyceride levels differed significantly among the three groups. Food intakes of HE and HS rats were similar, but HE rats had significantly lower final body weights. The results suggest that (1) exercise may ameliorate many of the changes in lipoprotein and cholesterol metabolism induced by a diet containing lard and cholesterol, and (2) some of these changes may be mediated by changes in hepatic lipoprotein production.

The effect of exercise and hyperlipemic diet on aortic histopathology in the rat

Histological changes in the aorta were used as criteria to assess the effect of treadmill exercise on the development of atherosclerosis in rats consuming a moderately hyperlipemic diet. While grossly visible atherosclerotic plaques were absent, microscopic examination of sections of the abdominal aorta were distinctly different between exercised and sedentary rats. Aortas of sedentary rats fed a diet containing lard and cholesterol had a high degree of plaque development, fat accumulation, mineralization, erosion and necrosis. Aortas of exercised rats fed the same diet had considerably less atherogenic involvement. Both hyperlipemic groups had greater plaque formation than sedentary rats fed a normolipemic diet. In addition, there were marked differences in plasma lipids; exercise ameliorated the diet-induced changes in plasmatic atherogenic lipids. Our results indicate that exercise retards the development of atherosclerosis in rats fed a hyperlipemic diet.

Platelets, carotids, and coronaries. Critique on antithrombotic role of antiplatelet agents, exercise, and certain diets

"Antiplatelet" drugs and certain life styles seem to have an "antithrombotic" effect that may help protect against stroke and heart attack. This review of the experience with aspirin, dipyridamole, and sulfinpyrazone offers new interpretations of some of the major clinical trials, suggests guidelines for use of antiplatelet drugs, and integrates novel observations on diet and exercise into the "thromboxane-prostacyclin balance" hypothesis. It is argued that the Canadian stroke study showed that aspirin protects men with transient ischemic attacks from coronary death as well as from stroke, that type II errors may have been made in some clinical trials, that aspirin protects women as well as men, that aspirin benefits patients who have had a heart attack, that the effect of aspirin in angina varies with the type of angina, that the dose of aspirin used may not be critical, that guidelines for use of dipyridamole and sulfinpyrazone are still inconclusive, and that exercise and fish oil supplements may be "antithrombotic."

Current concepts in cardiac rehabilitation

This article has presented the historical basis for cardiac rehabilitation and the available data related to the four most important questions that remain: (1) Does exercise increase survival after myocardial infarction? Although it is generally thought that clinical trials have failed to demonstrate that cardiac rehabilitation prolongs life after a myocardial infarction, analysis of pooled data from all published studies shows that this conclusion is unjustified. (2) Can each individual patient's risk for a future cardiac event be determined? We have developed a method using serial application of Baye 's theorem to determine each patient's risk. By so doing, we can stratify patient groups by previous risk and then assess the effect of cardiac rehabilitation on altering risk without limiting the analysis to subsequent myocardial infarction and cardiac death. (3) Can regression of atherosclerosis be demonstrated? Regression of atherosclerosis has been clearly demonstrated in animal models, but new evidence suggests that it can also occur in human subjects. (4) Do all patients require monitored exercise after a myocardial infarction? Evidence documenting the safety of exercise in patients recovering from a myocardial infarction has resulted in inclusion of sick patients in cardiac rehabilitation programs and exercise of the healthier patients in unmonitored settings. Major changes in cardiac rehabilitation programs are now taking place, with the emphasis moving away from prolongation of life toward improvement in the quality of life. As a result, cardiac rehabilitation is no longer confined to exercise alone; equal emphasis is placed on dietary and psychologic aspects of patient recovery.