EFFECTS OF PHYSICAL TRAINING ON THE CARDIOVASCULAR AND RESPIRATORY RESPONSE TO GRADED UPRIGHT EXERCISE IN DISTANCE RUNNERS

The Q˙-V˙O2 diagram: an analytical interpretation of oxygen transport in arterial blood during exercise in humans

A new analysis of the relationship between cardiac output (Q˙) and oxygen consumption V˙O2 is presented (Q˙-V˙O2 diagram). Data from different sources in the literature have been used for validation in three conditions: exercise and rest in normoxia, and exercise in hypoxia. The effects of changes in arterial oxygen concentration CaO2 on Q˙ are discussed, as well as the effects of predominant sympathetic or vagal stimulation. Differences appear depending on whether CaO2 is varied by means of changes in blood haemoglobin concentration or changes in arterial oxygen saturation. The present Q˙-V˙O2 diagram allows comprehensive description of oxygen transport in exercising humans; it expands applicability of the historical Q˙-V˙O2 relationship to include CaO2 variations; it opens new pathways for understanding underlying mechanisms; it allows computation of Q˙ from CaO2 and V˙O2 measurements, when Q˙ cannot be measured.

Cardiac rehabilitation following myocardial infarction. A practical approach

The concept of cardiac rehabilitation following myocardial infarction is not a new one but is now at last gaining acceptance as an essential part of the service to the coronary patient. Its aim is to restore the effectiveness of post-infarct patients by ensuring that they are well adjusted, well educated and fit and thereby best able to cope with the long term consequences of their ischaemic heart disease. The first essential factor for good rehabilitation is patient education. Studies have shown high levels of distress and anxiety after infarction and to a large extent this is related to lack of information. Where patients have been given adequate information concerning their condition and treatment there is a high level of patient satisfaction and greater compliance. It must be appreciated that stress and anxiety impair the patient's ability to assimilate information and therefore repeated reinforcement is necessary. During the in-hospital period, the staff who are caring for the patient are constantly changing and while there is a role for all to educate the patient, the use of a cardiac liaison sister provides a continuity throughout the early recovery period to ensure that the education process is adequate. The use of written material and both audio and video tapes is also helpful. It is also important for the liaison sister to extend her role to the patient's immediate family, who also require information, and finally the liaison sister can provide a link into the post discharge phase, to answer the many questions that arise at this time, and to provide encouragement to the patient who is attempting to modify his lifestyle by stopping smoking, changing his diet and taking regular exercise. The use of exercise training is the second vital ingredient for adequate rehabilitation. This begins in earnest after the 6-week assessment, which can provide information on which to base an exercise prescription. The majority of patients enrolled within exercise programmes are medically stable and relatively symptom-free. There is increasing evidence that those with extensive myocardial damage, left ventricular dysfunction or failure, and ongoing myocardial ischaemia may also benefit. Traditional training programmes have been hospital based and have used mainly aerobic exercise. However, home based programmes should not be discounted where they may be more economical, more convenient, and improve patient compliance. Similarly, circuit training with weights has been shown to improve aerobic endurance and muscle strength and to have additional benefits in improved treadmill time compared with traditional aerobic programmes.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular and respiratory responses to submaximal exercise training in the thoroughbred horse

Cardiovascular and respiratory responses to submaximal exercise training were investigated in 6 thoroughbred racehorses. Oxygen uptake, heart rate (HR) and arteriovenous oxygen content difference were measured during incremental treadmill exercise tests, before and after 7 weeks of treadmill training. Cardiac output during exercise was calculated by the direct Fick technique. Maximal oxygen uptake (VO2max) was increased by 23% after training, from 129.7 ml/kg/min to 160.0 ml/kg/min. The treadmill speed at which VO2max was attained increased by 19%. The increased aerobic power after training was associated with an increase in maximal cardiac output and stroke volume, a decrease in arteriovenous oxygen difference and no change in HR. There was no change in pulmonary ventilation during exercise at VO2max. Mean mixed venous oxygen content (CvO2) at VO2max before training was 2.8 +/- 1.0 ml/100 ml blood (mean +/- SE). After training the value was 8.6 +/- 1.4 ml/100 ml blood. It is concluded that the increase in VO2max after training in the horse is dependant on augmented blood flow, and is not dependant on either increased arterial oxygen content or arteriovenous oxygen content difference. Cardiac capacity to pump blood is therefore of primary importance as a determinant of increases in VO2max due to training in the horse.

Influence of beta-adrenergic blockade on the hemodynamic effects of physical training in patients with ischemic heart disease

Beta-blocking agents are widely used in the treatment of patients with coronary artery disease. Their negative chronotropic and inotropic actions may alter the effects of physical training in cardiac rehabilitation programs. Therefore, resting and exercise cardiac output, stroke volume, heart rate, and arteriovenous oxygen content difference were measured before and after training in 15 male patients with coronary artery disease, who were treated with beta blockers, and in a control group of 14 patients not treated with beta-blocking agents. At the end of a 3-month training period, oxygen uptake at peak exercise increased similarly in the two groups, 37% and 34%, respectively; this was related to increases in stroke volume and heart rate, and therefore cardiac output, and to increases in arteriovenous oxygen content difference. The effects were similar whether or not the patients were treated with beta blockers. Also, at rest and submaximal exercise, beta blockade did not affect the training-induced changes of cardiac output, heart rate, and arteriovenous oxygen content difference. In both groups heart rate decreased with training while stroke volume and cardiac output increased significantly. In conclusion, beta blockade did not significantly alter the hemodynamic effects of training.

Predicting the exercise catastrophe in the post-coronary patient

A total of 230 patients attending an exercise-centred rehabilitation program have been divided into those engaged in physical activity and those inactive, at the time of their first infarction. The two groups have identical physical characteristics, initial fitness levels, and responses to laboratory exercise; the only distinguishing features of the 'active' group is a somewhat longer and more sharply localized pain during infarction and a greater response to exercise training. Since the potential victim of the exercise catastrophe cannot be identified, prevention rests upon careful counselling of all 'post-coronary' patients. Excessive and unusual exertion should be avoided, particularly when this is associated with competition and emotional excitement. Patients should also learn to recognize the symptoms associated with dysrhythmia and angina, and should moderate their physical activity schedule if they sense ischemial prodromata, mental tension or depression.Despite the large size of the exercise class, a good training response (13%-21% gain of aerobic power in one year) is being sustained. Despite objective evidence of effective cardiorespiratory training, systemic blood pressures remain unchanged, both at rest and during standard laboratory exercise.

Increased arteriovenous oxygen difference after physical training in coronary heart disease

A preliminary study of 12 male patients (mean age, 47.8 years) with coronary heart disease (six with angina pectoris and six with prior myocardial infarction but without angina) was conducted according to a common protocol in Seattle, Washington, and Louvain, Belgium. Maximal oxygen intake (V o o2 max) and hemodynamic studies at rest and at two or three levels of submaximal exercise in the upright position were obtained before and after a 3-month physical training program that involved three sessions of 45 min/week. "V o o2 max" increased 22.5% ( P < 0.0001) with physical training. Changes in maximal heart rate occurred in the patients with angina (+8.4%) but not in those without angina (+0.8%). At rest and at each submaximal exercise, heart rate, mean blood pressure, and cardiac output decreased after training, whereas stroke volume was unchanged and arterio-mixed venous oxygen (A-V o o2 ) difference increased. The pressure-rate product and the left ventricular work decreased after training. The classic posttraining bradycardia was compensated not by a higher stroke volume but by an increased A-V o o2 difference which resulted from both a higher arterial oxygen content and an increased peripheral oxygen extraction. The latter was more apparent when exercises of the same relative intensity were compared.

Thus, benefits with physical training in coronary patients result at submaximal exercise level from enhanced arterial oxygen content and peripheral extraction and secondarily from lower hemodynamic stress on ischemic myocardium. Increased maximal A-V o o2 difference probably explains most of the increase in "V o o2 max" with physical training in coronary patients not limited by angina pectoris.

Physical training in the management of coronary artery disease

The effects of 4 to 6 weeks' physical conditioning on the cardiovascular and respiratory response to exercise were studied in nine patients with coronary artery disease. Clinical improvement and increased physical working capacity were observed in all patients. The average cardiac output during exercise was unchanged. The stroke volume increased and the myocardial work, assessed by the tension-time index, decreased during exercise at a given work load. It is suggested that at submaximal work loads a reduction of the blood flow to the working muscles occurs after training. Such change might be fundamental for the altered circulatory regulation by allowing a reduced general sympathetic vasoconstriction during exercise. It is concluded that the hemodynamic changes form a rational physiologic basis for the use of physical training in the management of patients with coronary artery disease.

Exercise and intermittent claudication. Blood flow in the calf muscle during walking studied by the xenon-133 clearance method

Nineteen patients with obliterative arteriosclerotic disease of the legs and suffering from intermittent claudication were studied before and during a 6 months' training program. The maximal walking distance and the calf muscle blood flow during walking (xenon-133 clearance technique) was recorded at monthly intervals. A significant correlation was established between improvement in maximal walking distance and a change on exercise toward more normal (that is, more adequate) blood flow in the calf. In particular, it was found that calf muscle blood flow during walking was increased by physical training. The data suggest that functional factors (for example, better coordination of the working muscles or a decrease of in-between-step intra-muscular pressure) as well as anatomic factors (increase in number or diameter of collateral vessels, or both) are involved in increasing collateral efficiency.

Effects of physical training in dogs with coronary artery ligation

This experiment was designed to determine whether physical conditioning can be achieved in the presence of acute myocardial infarction and whether such an exercise program is harmful. For this purpose the effects of a 5-weeks' treadmill-exercise program and inactivity were compared in two groups of dogs in which acute myocardial infarction was produced by coronary artery ligation.

The exercised group of animals tolerated the training program well, and neither arrhythmia nor sudden death occurred. At the end of the training program the exercised group of animals displayed the characteristic changes of physical conditioning, namely, reduction in exercise heart rate, cardiac output, and blood lactate levels; rise in circulating epinephrine levels with exercise was also suppressed by conditioning. Postmortem examination revealed neither ventricular dilatation nor aneurysm formation.

Comparative exercise-cardiorespiratory performance of normal men in the third, fourth, and fifth decades of life

The circulatory and respiratory responses to five levels of treadmill exercise were recorded for 75 normal males divided equally in the age groups 20 to 29, 30 to 39, and 40 to 49 years. Parameters studied included heart rate, cardiac output, stroke volume, intra-arterial blood pressure, minute ventilatory volume, oxygen uptake, and carbon dioxide elimination. Values for peripheral vascular resistance, left ventricular work, and stroke work indices were calculated. Intergroup and intragroup differences were analyzed by modified covariance technique using oxygen uptake per square meter of body surface area as the concomitant variable reflecting a specific midrange work level. Significant differences were observed between groups in cardiac output, stroke volume, systolic, diastolic, and mean arterial blood pressure as well as pressure-related variables with regard to absolute values and trend over the exercise spectrum. The results indicate that normal untrained males in the fourth and fifth decades of life react to moderate and heavy upright exercise with statistically significant systemic pressure elevations as compared to 20-year-olds. A tendency toward initially high cardiac output and stroke volume during light exercise was observed in the older men. Relatively small subsequent increments in cardiac output with resultant low absolute values during heavier work were also characteristic for this group as reflected in their decreasing stroke output at submaximal loads.