Influence of age on sensitivity and effector mechanisms of the carotid baroreflex

In 30 healthy subjects aged 20--48 years the hemodynamic response to carotid sinus stimulation (neck suction -40 mmHg) was studied. Heart rate, arterial pressure and cardiac output (dye dilution technique) were measured. In order to evaluate the effect of age on carotid sinus function the material was subdivided into two arbitrary subgroups, aged up to 30 years (n = 15) respectively 30 years and above (n = 15). Carotid sinus stimulation induced a significantly greater reduction in mean arterial pressure in the younger group compared to the older group. The heart rate reduction was, on the average, slightly greater in the younger group though the difference was not significant. In both groups a significant decrease in cardiac output contributed to the demonstrated reduction in mean arterial pressure. As the decrease in cardiac output was, on the average, slightly smaller in the younger group, the results indicate that the greater blood pressure response in the younger group was due to a greater reduction in peripheral vascular resistance. This is further supported by the finding of a significant correlation between changes in total peripheral vascular resistance, elicited by carotid sinus stimulation and age.