Cardiopulmonary Adjustments During Exercise and an Aversive Reaction Time Task: Effects of Beta‐Adrenoceptor Blockade

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Abstract
The purpose of this study was to compare the cardiopulmonary and hemodynamic adjustments to a physical (bicycle exercise) and behavioral (aversive reaction time) stressor. A related aim was to assess the role of beta‐adrenergic mechanisms in mediating these physiological responses. Thirty‐four subjects were exposed to both stressors while oxygen consumption, carbon dioxide production, pulmonary ventilation, end‐tidal oxygen and carbon dioxide, as well as heart rate were calculated breath‐by‐breath. Fourteen of these subjects were pretreated with 4 mg (iv) of propranolol hydrochloride. The remaining 20 subjects (intact) were subdivided post‐hoc into the 10 most and 10 least reactive on the basis of their heart rate response to the reaction time task. The results indicate that for the intact group both exercise and the reaction time task produced significant increases in heart rate although the magnitude of the heart rate change was reliably greater during exercise. Beta‐adrenergic blockade partially diminished the tachycardia to exercise but entirely abolished the tachycardia to behavioral stress. Interestingly, the most and least reactive subjects did not exhibit differential heart rate acceleration during exercise despite a reliable difference during the reaction time task. Oxygen consumption significantly increased to predictable levels during exercise but failed to change during the reaction time task for both the most and least reactive groups. These results suggest that the tachycardia elicited by the reaction time task in reactive subjects was not associated with an appropriate increase in oxygen consumption, relative to exercise, and may therefore be indicative of systemic overperfusion.