Abstract
A great number of research has been directed toward identifying the biological mechanisms of increased risk of coronary heart disease (CHD) among Type A persons. It was often reported that Type A's showed greater cardiovascular responsivity, especially beta-adrenergic, than Type B's during various stressful situations. Recent evidence from our laboratory, however, has suggested a tendency for enhanced alpha-aderenergic and vagal reactivity in Type B individuals. which led to the hypothesis that Type A's and Type B' s might differ in general autonomic balance. In order to test this hypothesis, the present study investigated cardiovascular reactivity of young healthy male Type A (n=11) and Type B (n=13) subjects during mental arithmetic (MA), which, dominantly elicits a betaadrenergic response, and cold face stimulus (CFS), which mainly elicits alphaadrenergic and vagal responses. There was no group difference in response to Ma. However, during CFS, Type B's showed more prolonged decrease in heart rate (p<0.02 : ANOVA) and forearm blood flow (p<0.03) as the increase in systolic blood pressure (p<0.03) and diastolic blood pressure (p<0.03). These findingo suggested that. Type B's exhibited alphaadrenergic and parasympathetic hyperreactivity in contrast with enhanced betaadrenergic responsivity in Type A's. Such differences in autonomic balance might account for the different CHD risk among the people with Type A and Type B behavior patterns.
