Sympatho-vagal changes induced by physical training in cardiac patients

Heart-rate and blood pressure increase correlate proportionally to myocardial oxygen consumption. A 100% increase in stroke volume, however, is related to only a 10% increase in myocardial oxygen consumption (Sarnoff et al., 1958). An economical cardiac adaptation to exercise which results in a saving of myocardial oxygen requirements (Heiss et al., 1979) is therefore based on an increased stroke volume in relation to a moderate heart-rate response and a decrease in circulatory resistance, respectively. Such a cardiac adaptation to exercise can be observed in endurance-trained subjects, dependent on a reduction in sympathetic activity and an increase in vagal tone. This favourable change in sympatho-vagal tone can be expected in all subjects undergoing physical training (endurance training) and in part also in some cardiac patients subsequent to physical therapy. However, only an approximate normalization of impaired autonomic function can be observed as a result of physical therapy in patients with significantly reduced exercise capacity, and this in less than 50% of the investigated cardiac patients. In cardiac patients with normal exercise capacity and approximately normal or slightly decreased left ventricular function, a favourable improvement in autonomic function and an increase in exercise capacity can be expected in about 50% of cases. The possibility or the extent to which the prognosis of cardiac disease is affected by the change in autonomic function remains unclear, however.