Haemodynamic response to graded exercise during chronic beta-adrenergic blockade with bunitrolol, an agent with intrinsic sympathomimetic activity.

The effect of chronic beta blockade on the haemodynamic response to graded exercise was studied in 18 hypertensive patients treated with bunitrolol, which has partial agonist activity. The patients first received a placebo for 5 to 12 days, then bunitrolol 30 mg daily for one week and subsequently the dose was doubled weekly as necessary up to 240 mg daily. At rest haemodynamic changes after beta blockade were only minor; heart rate decreased by 8% and no significant change was observed in stroke index, cardiac index, (a-v)O2 difference and VO2. The hypotensive effect was not significant and no significant change in mean pulmonary arterial and wedge pressure was observed. Maximal exercise capacity remained unchanged, because of haemodynamic responses. The maximal exercise heart rate was reduced by 25% during beta blockade, which was compensated by a 34% elevation in stroke index, whereas maximal cardiac index and (a-v)O2 difference remained unchanged. There was no consistent change in mean pulmonary artery pressure during maximal exercise, but the mean brachial artery pressure fell by 12%.