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Most studies with conventional ECG lead system have emphasized the reduction of electrical forces of the heart under physical exercise. However, there have been few systematic vectorcardiographic observations in the graded exercise. This study represents vectorcardiographic and cardiodynamic analyses in exercise by a bicycle ergometer performed on 51 subjects comprising 18 normal controls, 10 normal seniles, 7 hypertensives and 16 patients with ischemic heart disease. Vectorcardiogram with Frank orthogonal lead system was recorded before and after each exercise trial and X-Z component electrocardiogrms were monitored throughout whole procedure. Electrical systole, isometric and isotonic contraction periods during exercise were evaluated by simultaneous recordings of ECG with Nehb-D, PCG and externally recorded carotid artery pulse wave. As a control, graded interrupted exercise with the doses of 50, 75 and 100 watts for 6 minutes were given to 12 normal subjects. saQRS showed parallel increase in the magnitudes to increased exercise doses and directed to the right anterior and superior octant. Spatial angles between saQRS and saT represented by delta' showed gradual increase on each step of the graded exercise. A single exercise dose of 1.0/kg given to other subjects including normal seniles, hypertensives and patients with ischemic heart disease. Vectorcardiographic changes in normal seniles over 60 years of age were essentially same to normal control subjects. In the group with ischemic heart disease, there were two different types of VCG changes. In one, abnormally small saT and sVG were characteristically increased after the exerise. In the other with almost normal saT and sVG, changes in VCG were similar to the control. Cardiac dynamics during exercise revealed decreased isometric and isotonic contraction periods and increased ATZ/ASZ ratio in each group. No characteristic cardiodynamic changes were observed in normal seniles or patients with ischemic heart disease.

VECTORCARDIOGRAPHIC OBSERVATIONS IN THE GRADED EXERCISE BY A BICYCLE ERGOMETER