Influences of physical conditioning and deconditioning on coronary vasculature of dogs

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.

Decreased incidence of ventricular fibrillation after an acute coronary artery ligation in exercised pigs

Evidence has been presented that regular physical activity may be associated with a decreased incidence of sudden cardiac death. It has been suggested that self-selection of those engaging in regular exercise rather than the physical activity itself is a major factor in explaining these results. We therefore studied the effects of a two-month exercise program on the incidence of ventricular fibrillation after an acute ligation of the left anterior descending (LAD) coronary artery in domestic Yorkshire pigs. At the end of the exercise program, the exercised group (EG, n = 17) had a lower heart rate (10%), a 5 times higher maximum exercise capacity, a 10% larger left ventricular mass and a thicker myocardial wall during end-diastole than a sedentary group (SG, n = 13). After the animals were anesthetized, the LAD artery was occluded at one third of its distal end. Ventricular fibrillation (VF) occurred in 92% of the SG (12 out of 13) against only 30% of the EG (5 out of 17) within 1 hour after occlusion. Percentage of the area at risk was the same (9-10% of total left ventricular mass) in both the EG and SG. Transmural myocardial perfusion after coronary artery ligation was slightly larger in EG than in SG (30 vs 21 ml . min-1 . 100 g-1, p less than 0.05). Although the improvement in perfusion of the ischemic zone of the EG may have contributed to the reduced occurrence of ventricular fibrillation, other mechanisms cannot be excluded.

Effects of physical training on myocardial vascularity and perfusion

Physical training is thought to be a stimulus for coronary vascular growth and coronary collateral development. This report is a summary of knowledge in the area. Studies in experimental animals with normal hearts indicate that physical training promotes increased myocardial capillary density and also causes enlargement of the surface coronary vessels. The physiologic effect of these changes on coronary vascular reserve and protection of segments of the heart against myocardial ischemia has not been established. Physically trained dogs and pigs do not appear to be protected against the effects of coronary occlusion, in that the ischemic area appears to be as large in trained animals as in untrained animals for any given coronary lesion. One study in physically trained rats appears to show protection against myocardial infarction, but whether this is related to coronary vascular changes has not been established. Experiments in dogs subjected to chronic narrowing or gradual occlusion demonstrate that physical training in these models does promote collateral blood flow as measured by retrograde flow in open-chest experiments. Studies using the microsphere technique in closed-chest animals confirms increased collateral flow to ischemic areas in some animals, but the magnitude of the increases appears to be small and varies greatly from animal to animal. Studies in athletes suggest that myocardial blood flow is lower at any submaximal level of training in athletes than in sedentary persons. Studies in patients with coronary artery disease have generally failed to show an increase in coronary blood flow or in perfusion of ischemic areas after physical training programs, but the techniques used might not have been sensitive enough to detect changes. The evidence in the experimental animals is sufficiently promising to indicate that the search should be continued to define physical training programs that will most stimulate myocardial vascularity and coronary collaterals in humans.

Noninvasive assessment of changes in myocardial perfusion and ventricular performance following exercise training

Seventeen coronary patients (CAD) underwent thallium (TI-201) treadmill and radionuclide (RNV) ejection fraction supine bicycle testing before and after 5.6 +/- 1.6 (mean +/- SD) months of an exercise program. Thallium data were assessed both using analog images and a computerized circumferential profile technique. Patients exercised on the treadmill to a higher workload after the exercise program, but achieved a similar pressure-rate product. When interpreting the analog thallium images, only 50% agreement was obtained for the assessment of changes in myocardial perfusion (pre/post-training). The computer technique, however, had low inter-intraobserver variability (6%) and better agreement (90.5%). Using the circumferential profile method, five patients improved (a total of 11 regions) and one patient worsened (with two regions). Before the exercise program, the ejection fraction (EF) response to supine bike exercise was normal (an increase greater than 11%) in four, flat in seven, and severely abnormal (a decrease of more than 4%) in six patients. After the exercise program, even though achieving similar or higher pressure-rate products, six patients improved their EF response, nine did not change, and two worsened. Of the five patients who improved their thallium images, one improved his EF response, two remained normal, and two did not change. One patient worsened both his thallium study and the EF response after the exercise program. Changes in thallium exercise images and the EF response to supine exercise occurred in our patients after an exercise program, but were not always concordant. Indeed, of five patients with exercise-induced ischemic ST changes before and after training, the EF response improved in three whereas myocardial perfusion was unchanged. Reasons for this lack of agreement are discussed, and have been considered in the planning of a randomized trial of the effects of an exercise program on myocardial perfusion and function.

Effects of Diet and Exercise on Peripheral Vascular Disease

In brief A 46-year-old man presented with symptoms of peripheral vascular disease in 1966. In 1976 arteriography revealed 100% occlusion of both femoral arteries at midthigh and some reconstitution of flow via collaterals into the popliteal region. His cholesterol level was initially 407 mg/100 ml, and his walking tolerance was 100 yards. After a 26-day stay at the Pritikin Longevity Center, his cholesterol dropped from 230 mg/100 ml to 130 mg/100 ml, and his walking tolerance increased to 3 miles in one hour with little leg pain. He has run more than 20 road races and completed a marathon. A recent exercise Doppler exam and a second arteriogram indicated a significant increase in blood flow due to dilation of deep femoral arteries and existing collateral vessels.

Chronic exercise and cardiac vascularization

Male albino rats were trained on a motorized treadmill for 8 weeks, using eight training regimens which varied in severity from 0.313 m . s-1, 3 days/week for 30 min each day, to 0.447 m . s-1, 5 days/week for 60 min each day. At the end of the 8 week training period, the animals were anesthetized and Pelikan ink infused retrogradely through the aorta, into the coronary arteries and capillaries of the heart. The hearts were sectioned, stained and examined for the number of capillaries per mm2 and the capillary/muscle fiber (C/F) ratios. Six of the eight exercise groups had capillary densities significantly lower than the density in the sedentary control group of 3,022 cap mm-2. Likewise, five of the exercise groups had significantly lower C/F ratios than the sedentary group ratio of 1.077. The difficulties inherent in identification of cardiac muscle fibers make the C/F ratio a weaker measurement for determining cardiac vascularity. The lower capillary density in the trained hearts could be produced by muscle fiber hypertrophy which would push the capillaries farther apart. It is concluded that exercise training does not stimulate the multiplication of cardiac capillaries. The beneficial effect of exercise on the heart is probably a result of enlargement of the coronary arteries or the collateral circulation.

Long-term vasotonus behavior of the microvasculatory system of heart and skeletal muscle in rats exercised by swimming

A new histomorphometric method was used to study the hitherto unknown long-term vasotonus behavior of the arterial microvasculatory system. The right and the left ventricular walls of 29 rats exercised by swimming (48 hours in 4 weeks), and 30 control animals, as well as the musculus rectus femoris of 5 experimental and 5 control animals were investigated. The walls of arterial microvessels of the right ventricular wall and of the skeletal muscle of trained rats were significantly thicker indicating a long-term vasotonus increase. In the microvasculature of the lift ventricular wall no differences were found in comparison to control animals. In view of the vasotonus increase in the right ventricular wall and skeletal muscle, one can assume that tonus-decreasing factors of nearly the same intensity and/or duration of efficiency have opposed the tonic influences in the left-ventricular microvessels, thus preventing a thickening of vessel walls.

Effects of 12 months of intense exercise training on ischemic ST-segment depression in patients with coronary artery disease

This study was undertaken to determine whether adaptation to 12 months of intense endurance exercise training could alter the relationship between the product of heart rate and systolic blood pressure (double product) and the extent of ischemic ST-segment depression during exercise in patients with coronary artery disease. True (i.e., not symptom-limited) maximum oxygen uptake capacity increased from 25.5 +/- 4.2 ml/kg/min (mean +/- SD) to 35.3 +/- 4.4 ml/Kg/min with training. The maximum degree of ST-segment depression during exercise averaged 0.20 +/- 0.04 mV before and 0.16 +/- 0.08 mV after training despite a 20% increase in maximum double product. The double product at which ST depression (0.1 mV) first appeared was 22% greater after training. The extent of ST-segment displacement at the same double product was less after training. These findings suggest that training, if sufficiently intense and prolonged, can result in a reduction in myocardial ischemia at the same or a higher double product.