Abstract
The slowing of heart rate prior to an anticipated action is puzzling. Increased heart rate would seem biologically more appropriate. Beat-by-beat vascular measures were studied in order to see if heart rate slowing was associated with improved blood flow to the limb involved in the anticipated action. In 27 men, pulse wave velocity (PWV), pulse transit time (PTT), and pulse amplitude measures were collected from arterial and thumb sites. A paced auditory reaction time (RT) task with two levels of reward (incentive) was used. Beat-by-beat results showed a concomitance of heart rate slowing, PTT shortening, and pulse amplitude increase. These changes were interpreted as being due to vagal effects and their hemodynamic consequences. Pacing RT at fast speeds led to an elevated PWV, which suggested alpha sympathetic activation during periods requiring substantial effort. Tentatively, the results suggest that heart rate slowing is one aspect of an adaptive cardiovascular adjustment by joint vagal and alpha sympathetic activation.
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