BRADYCARDIA DURING BAROREFLEX STIMULATION AND ACTIVE OR PASSIVE STRESSOR TASKS - CARDIORESPIRATORY FITNESS AND HOSTILITY

We examined whether the resting bradycardia associated with cardioresp iratory fitness extends to lowered heart rate (HR) and mean arterial p ressure during novel passive or active laboratory stressors and to a l onger heart period during stimulation of the carotid-cardiac vagal bar oreflex, independently of the Type A behavior pattern (TABP) and hosti lity. Forty-four normotensive Caucasian men (18-35 years of age) compl eted the Structured Interview for TABP, the Cook-Medley Hostility Scal e, and a peak oxygen uptake (Vo(2peak)) test. Vo(2peak) was inversely related to HR prior to, during, and after each stressor and was positi vely related to heart period during baroreflex testing. Hostility was inversely related to heart period during baroreflex testing. TABP had no effects. Our findings indicate that cardiorespiratory fitness and l ow hostility are independently associated with a bradycardia during st imulation of the carotid-cardiac baroreflex, consistent with a possibl e enhancement of cardiac vagal tone.