Influence of beta-adrenergic blockade upon hemodynamic response to exercise assessed by Doppler echocardiography.

Peak aortic blood flow acceleration and velocity measured by Doppler echocardiography have been documented to be accurate descriptors of left ventricular systolic function. Both acceleration and velocity are reduced in the presence of beta-blockade at rest and during exercise. Whether and to what extent the simultaneous alterations in heart rate (HR) due to beta-blockade affect these parameters has received little study. In order to determine the influence of alterations in HR on Doppler measurements of velocity and acceleration, 10 healthy men were studied during upright exercise under control conditions, following propranolol administration, and following propranolol plus transesophageal atrial pacing. In addition, we assessed the response of stroke volume (measured as flow velocity integral) during beta-blocked and control exercise. Propranolol significantly reduced acceleration and velocity during all stages of exercise compared with control values (p less than 0.05). Increasing the HR during exercise via pacing had no effect on acceleration or velocity compared with propranolol administration alone, thus demonstrating that during upright exercise, changes in acceleration and velocity are independent of alterations in HR. At low levels of exercise, propranolol significantly reduced flow velocity integral (FVI) compared with control (-1.14 cm, p less than 0.05.). At high levels of exertion, however, FVI exceeded values obtained during control conditions (1.2 cm at stage 4). Pacing during beta-blockade reduced FVI at high levels of exercise but had no effect at lower levels. Our results suggest that during low levels of exercise stroke volume is increased as a consequence of both increased contractility and augmented left ventricular filling.(ABSTRACT TRUNCATED AT 250 WORDS)