Comparative physiological study of arbutamine with exercise in humans

Pharmacological stress resting may be used in the diagnosis of coronary art ery disease when there are contra-indications to the use of conventional ex ercise protocols. The responses to such testing using arbutamine and to con ventional treadmill exercise were compared in eight patients. Respiratory g as analysis and cardiovascular observations were performed during both test s. For an equivalent increment in heart rate, both protocols increased syst olic blood pressure and serum lactate. Minute ventilation and oxygen consum ption also rose during both protocols, but much more so with exercise. The end-tidal partial pressure of CO2 [35.1 (S.D. 3.1) to 30.8 (6.6) mmHg] and the dead space/tidal volume ratio (V-D/V-T) [0.37 (0.09) to 0.33 (0.08)] fe ll significantly during arbutamine infusion, but the respiratory exchange r atio did not change during either protocol. Oxygen pulse, a marker of strok e volume, did not change significantly after arbutamine, but rose markedly after exercise [arbutamine, 3.9 (1.1) to 3.37 (0.7) ml.min(-1).beat(-1); ex ercise, 4.7 (1.4) to 16.1 (4.6) ml.min(-1).beat(-1) (P < 0.0001 compared wi th baseline); difference between peak responses: P < 0.0001]. We conclude t hat arbutamine simulates some of the physiological responses to exercise, a lthough a number of these responses are less marked than during conventiona l exercise, in particular cardiac output (oxygen pulse). An increase in ven tilation is produced, possibly due to direct stimulation of arterial chemor eceptors. These data suggest that the main action of arbutamine is to incre ase central drive rather than to establish peripheral demand.