Analysis of epidemiologic studies of physical inactivity as risk factor for coronary artery disease

Physical Exercise Is a Potential "Medicine" for Atherosclerosis

Cardiovascular disease (CVD) has been recognized as the number one killer for decades. The most well-known risk factor is atherosclerosis. Unlike the acuity of CVD, atherosclerosis is a chronic, progressive pathological change. This process involves inflammatory response, oxidative reaction, macrophage activity, and different interaction of inflammatory factors. Physical exercise has long been known as good for health in general. In recent studies, physical exercise has been demonstrated to be a therapeutic tool for atherosclerosis. However, its therapeutic effect has dosage-dependent effect. Un-proper over exercise might also cause damage to the heart. Here we summarize the mechanism of Physical exercise's beneficial effects and its potential clinical use.

The association of self-reported employee physical activity with metabolic syndrome, health care costs, absenteeism, and presenteeism

OBJECTIVE

To examine employees' self-reported physical activity and metabolic syndrome (MetS) risks and their association with health-related workplace outcomes.

METHODS

Employees participated in a health risk appraisal in 2010. Generalized Linear Modeling was used to test the association between MetS risk factors, physical activity, and the outcome measures while controlling for confounders.

RESULTS

MetS was found in 30.2% of employees. Health care costs for employees with MetS who reported sufficient exercise (150 or more minutes/week) totaled $2770 compared with $3855 for nonsufficient exercisers. The percentage of employees with MetS who had absenteeism and presenteeism was also significantly lower for employees achieving sufficient physical activity. All risk factors for MetS were mitigated for regular exercisers.

CONCLUSIONS

Employers should consider programs and services to support regular aerobic exercise to address the growing prevalence and costs of MetS in the workforce.

Assessment of work performance in asthma for determination of cardiorespiratory fitness and training capacity

In view of the lack of objective information on work performance in asthma, a progressive incremental exercise test was carried out in 44 subjects with mild to moderate asthma and 64 normal, healthy subjects matched for habitual activity, to compare cardiorespiratory fitness and to determine the relative contribution of airflow obstruction to exercise limitation. The two groups achieved similar maximum heart rates (mean (SD) 176(12) and 175(10) beats/min). After allowance for confounding factors the asthmatic subjects had a lower maximum oxygen consumption (VO2 max) (by 199 ml min-1) than control subjects. Having asthma also accounted for a significant reduction in anaerobic threshold (125 ml min-1) and oxygen pulse (0.805 ml/beat). There was no correlation of FEV1 with VO2 max, anaerobic threshold, or oxygen pulse either before or after bronchodilator. The dyspnoea index (VE/MVV%) was increased in the asthmatic subjects at peak exercise, but was less than 60% in all subjects at a workload that produced 75% of the predicted maximum heart rate. Thus the asthmatic subjects had a maximum heart rate similar to that of normal subjects but the low VO2 max, anaerobic threshold, and oxygen pulse suggest suboptimal fitness, which was not directly due to airflow obstruction. All had sufficient ventilatory reserve to allow toleration of training at a work intensity adequate to permit improvements in cardiovascular fitness.

Changes in selected cardiorespiratory responses to exercise and in body composition following a 12-week aerobic dance programme

Cardiorespiratory and body composition changes were evaluated in 25 sedentary females, aged 18 to 30 years, following 12 weeks of aerobic dance training (3 days a week, 45 min a session). Fifteen subjects, from the same population, comprised a control group: they maintained their normal activity and dietary habits over the course of the study. Analysis of variance of the values for selected cardiorespiratory responses revealed that the aerobic dance programme produced training effects in the experimental group. These training effects were indicated by significant improvements in O2 pulse, VE, heart rate and perceived exertion during submaximal exercise. Significant improvements were also noted in VO2 max, maximal O2 pulse, VE max, maximal heart rate and maximal running time on the treadmill. Additionally, increases in lean body mass and body density, together with decreases in percentage body fat and the sum of four skinfold thicknesses were found to be significant for the experimental group. No significant improvements in any of these variables were found for the control group. It was concluded that this 12-week aerobic dance programme was successful in promoting beneficial changes in cardiorespiratory fitness and body composition.

Favourable levels of cardio-vascular health and risk indicators during childhood and adolescence

This paper is concerned with favourable levels of constitutional cardio-vascular health indicators during childhood and adolescence. A cross-sectional randomised sample of healthy Czechoslovakian children was investigated, because this population is habituated to a favourable life style. Twenty girls and 20 boys at ages 8, 12 and 16 years were recruited to the study. Statistical data for means and standard deviations are presented with regard to maximal aerobic power, haemodynamic variables such as arterial blood pressure, heart rate at submaximal and maximal muscular exercise, body fat content, blood lipids including total cholesterol and its fractions, high- and low-density lipo-proteins, fasting triglycerides and the apo-lipo-protein profile. The maximal oxygen uptake in absolute values increased with age in both sexes and the boys appeared to average higher than the girls at each age. When maximal aerobic power was expressed on a total body weight basis, boys appeared to average higher at age 16 years (56 ml X min-1 X kg-1) than girls (45.8 ml X min-1 X kg-1). The highest recorded heart rate for ergometric work averaged close to 200 min-1 in both sexes with no significant age differences. The diastolic blood pressure at rest did not change significantly with age or sex. Serum cholesterol levels were found to decrease significantly after puberty in boys (post-pubertal dip), but in the girls there was found no systematic change in mean values with age. When HDL was expressed as a percentage of total cholesterol there appeared to be no differences related to age and sex.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Exercise and heart disease. Epidemiology of the "exercise hypothesis"

The "exercise hypothesis" states that exercise protects against coronary heart disease. Reviewed herein is the epidemiologic evidence for and against the "exercise hypothesis." The weight of evidence supports the view that exercisers have a lower risk of coronary disease, but that vigorous exercise cannot always prevent progression of coronary atherosclerosis and does increase the risk of sudden death in persons with advanced coronary atherosclerosis. It is concluded that the "exercise hypothesis" is plausible, even likely, but still unproved.

High density lipoprotein and apolipoprotein A-i during physical inactivity. Demonstration at low levels in patients with spine fracture

Lack of physical activity appears to have deleterious effects on serum lipoproteins. Twenty-three patients who were completely immobilised by traumatic fracture of the spine had significantly lower (P < 0.001) plasma high density lipoprotein cholesterol (HDL-C) and apolipoprotein A-I levels than normally mobile paired control subjects. The low density lipoprotein cholesterol (LDL-C) levels of the immobile patients were not different from those of controls but the LDL triglyceride (LDL-TG) of the patients was increased. The patients had a significantly higher LDL/HDL-C ratio and HDL-C/apoprotein A-I ratio than the controls. These results suggest that the increased risk of ischemic heart disease in physically inactive people is partially accounted for by low plasma HDL levels. On the other hand, caution is needed in the interpretation of HDL findings in clinical conditions where the physical activity of the patients is limited.

Sudden Death and Jogging

Meticulous necropsy studies might help unravel the puzzle of deaths in seemingly healthy individuals; exercise stress testing is a useful screening device.

Beneficial effect of physical training on blood flow to myocardium perfused by chronic collaterals in the exercising dog

To determine the effect of physical training on collateral blood flow, we measured regional myocardial blood flow (MBF) by injecting 15 mu radioactive microspheres at rest and during exercise in 14 dogs with chronic coronary occlusive lesions. Seven dogs subsequently trained for 6 weeks while the other seven remained in kennels. Training effect was documented by decrease in heart rate during exercise that averaged 35 beats/min. MBF studies were repeated after 6 weeks. Myocardial samples were obtained from normally perfused zones (NZ) and from regions supplied via collaterals (collateral dependent zones or CZ). Initially, endocardial blood flow in CZ averaged 1.110 ml/min/g (83% of NZ, P less than 0.05) at rest and 1.36 ml/min/g (69% of NZ, P less than 0.05) during exercise, indicating relative underperfusion. Epicardial blood flow was equal in NZ and CZ. After 6 weeks MBF was not significantly changed in control animals. After training, however, MBF to underperfused endocardium of CZ during exercise was 39% greater than it had been prior to training. The epicardial portion of CZ (not exhibiting underperfusion) showed no change in MBF during exercise after training. Our data suggest that beneficial effects of training in coronary disease may include improvement in MBF to underperfused collateral-dependent portions of myocardium.

[The effect of an on the job training program -- stairclimbing -- on the physical working capacity of employees (author's transl)]

Following medical screening and physical fitness testing (W170) 52 voltuntary employees in a 31-story administration building were formed into matched pairs and randomly allocated into intervention (stairclimbing) and control (lift) groups. The intervention group was asked to climb at least 25 floors/workday or 125 floors/week. the control group was asked to use only the lift. The intervention time was 10 weeks. The physiological measurements were made before and after the intervention. The number of stairs climbed was recorded daily in a diary. The heart rate was recorded continuously over one workday before and during the interventions. The average quantity of training in the final intervention group (n = 19) was 29.9 floors/workday or 36,790 kpm/week and in the control group 4.6 and 5980 correspondingly. The average training frequency was 4.3 in intervention and 1.4 climbs/workday in the control group. The average number of continuous floors used during climbing was 7.0 in intervention and 3.4 in control group. The average number of minutes on heart rate level of 130-159 beats/min during one workday was 7.8 in intervention and 1.6 in control group. The W170 (W/kg) increased 17.8% and the predicted VO2max (ml/min/kg) 15.1% in intervention group. The difference between the intervention group and the control group was significant (p less than 0.01). It was concluded, that stairclimbing is a suitable on the job physical activity program for middle-aged, untrained men.

Alterations in ventricular mass and performance induced by exercise training in man evaluated by echocardiography

Few data are available regarding the effects of exercise training upon cardiac structure and performance in man. We evaluated the echograms of 24 normals before (PRE) and after (POST) 11 weeks of endurance exercise training. Conditioning consisted of a walk-jog-run protocol at 70% maximal heart rate for one hour four days per week. Training reduced heart rate and increased maximal duration and estimated oxygen consumption of treadmill exercise. Compared to PRE, the echogram in the POST training period revealed an increased left ventricular (LV) end-diastolic dimension (EdD), a decreased end-systolic dimension (EsD) and thus an increased stroke volume (EdD3-EsD3) and shortening fraction (EdD-EsD)/EdD). Cardiac output (CO) and peripheral vascular resistance (BP/CO X 80) were identical PRE and POST conditioning. Importantly, an increase in mean fiber shortening velocity was observed POST training as were increases in LV wall thickness, ECG voltage of S in V1 + R in V5, and LV mass. Thus endurance training was accompanied by increases in both LV dimension and mass as well as LV shortening fraction and contraction velocity as observed by echocardiogram.

The important role of fitness determination and stress testing in predicting coronary incidence

The question of whether there is some effect of status of cardiorespiratory fitness and exercise ECG abnormalities on occurrence of CHD other than their effect on the risk factors of serum cholesterol, blood pressure, glucose, and smoking seems to have been answered in the affirmative by this study. The relative prognostic importance of the measures considered here, the role of exercise, and the interrelationships between fitness, exercise, other risk factors, and CHD provide many interesting hypotheses for continued study. A future investigation will involve a large prospective study in which the risk function to be derived would include stress ECG and treadmill performance as predictor variables. The retrospective approach reported in this paper had certain limitations. It did, however, permit demonstration of new results because, essentially for the first time, all of the important risk factors are measured in the study population and can be evaluated simultaneously.

A 4-year prospective study of the relationship of different habitual vocational physical activity to risk and incidence of ischemic heart disease in volunteer male federal employees

A prospective study of coronary heart disease (CHD) was done in 2,635 volunteer male federal employees of postal, health, aerospace, and other agencies, aged 35--59 years at intake. The present analysis is concerned with 2,065 initially well whites, of whom 65 suffered clinical CHD during a 4 years of annual follow-up. The subjects differed markedly in their levels of habitual vocational physical activity, which is classified (1) by division into sedentary, moderate, and heavy activity groups, (2) by blue collar or white collar type of occupation, and (3) by calculated annual caloric expenditure for both vocational and non-vocational physical activities. Intake variables that were studied in relation to physical activity and the CHD incidence include age, serum cholesterol, systolic blood pressure, relative body weight, ECG abnormality, and cigarette smoking. Socioeconomic status (SES) is assessed by levels of education and income and by a combined SES categorization based upon both. Estimated composite CHD risk scores are based upon Framingham equations. The CHD risk factors, singly, as well as in a derived composite risk score, are higher for men with heavy compared to sedentary or moderate habitual physical activity. However, this is a spurious association found to be induced by differences of SES. Thus, when physical activity and SES are studied in a concurrent analysis, a higher CHD risk is significantly associated with lower SES status but not with differences of vocational physical activity. The CHD incidence in this population is studied in relationship both to the risk factors and physical activity by multivariate analysis, using the multiple logistic risk model. The incidence of CHD is significantly associated with age, serum cholesterol, systolic blood pressure, and cigarette smoking. It is not found to be associated with the type of occupation (i.e., blue or white collar), the level of reported habitual vocational physical activity, or the calculated total vocational plus nonvocational caloric expenditure in physical activity.

Value of exercise testing for screening asymptomatic men for latent coronary artery disease

Treadmill exercise testing identifies a group of men at high risk for coronary atherosclerotic heart disease. However, the predictive value and sensitivity limitations are obvious. An abnormal electrocardiographic response does not absolutely predict the presence of coronary atherosclerotic heart disease, and a normal response does not rule out this possibility. Thus in appropriate instances when the minimal risk of coronary angiography is justified this procedure can be used to determine the anatomic correlation of exercise-induced functional ST-segment changes.

Cardiovascular fitness in a selected group of dentists

Thirty-three dentists were studied as part of an exercise rehabilitation clinic in order to evaluate their cardiovascular capacity and coronary prone risk factors. Measurements were made of their physical work capacity, predicted maximal oxygen uptake, fatness, serum lipids and uric acid levels, pulmonary peak flow rates and personality Type A or B. The group as a whole exhibited a moderately high level of fitness and a very active life style which probably reflected their presence at a clinic of this type. Cardiovascular fitness varibles increased with age. This increase may be due to a need and desire on the part of the dentists to maintain their physical fitness as they become older. This need for improved self image may also be a factor in their joining an exercise rehabilitation clinic.