Stroke Volume and Peripheral Resistance during Infusion of Isoproterenol at a Constant Fixed Heart Rate

THE hemodynamic effects of isoproterenol have been described in the literature in a variety of clinical1-2 and experimental conditions.13-16 In these reports, the action of this drug on the heart rate and stroke volume has been emphasized. However, no attempt has been made to study its hemodynamic consequences in man when the heart rate is maintained constant throughout the experiment. Under this circumstance it is possible to separate the peripheral from the central effects of this drug on the circulation. In previous reports'7' 18 we emphasized that exercise in patients with heart block at a fixed heart rate resulted in a marked increase in the stroke volume and cardiac output. Bruce, Cobb, Katsura, and Morledge'9 have suggested that isoproterenol can be used to mimic some of the effects of exercise, by virtue of its action on the cardiac output, stroke volume, and heart rate. This study was undertaken in order (a) to determine the hemodynamic consequences of isoproterenol in patients with complete heart block at a fixed heart rate and (b) to compare the effects of this drug with the ones produced by exercise at a constant fixed heart rate.