Die invloed van ouderdom as modulerende faktor tydens kardiovaskulêre reaktiwiteit

Abstract

The reactivity hypothesis postulates that increased cardiovascular reactivity as a consequence of the application of acute laboratory stressors is associated with the prognosis of hypertension (Matthews et al., 1993). The usefulness of the reactivity hypothesis is limited by the conflicting results of a number of studies (Anderson, 1993). It appears as if various factors influence the relationship between hypertension and hyper reactivity, e.g. the type of stressor and age. Different types of stressors, depending on whether the stressor is primarily physical, cognitive or psychological, give rise to different autonomous discharge patterns and cardiovascular reactivity patterns. The following hypothesis was investigated: changes in cardiovascular' reactivity with an increase in age partially occur due to physical changes in the cardiovascular system, and whether cardiovascular reactivity increases or decreases with age will depend on the autonomous discharge pattern, as induced by the specific stressor. Indirect continuous blood pressure was recorded by means of the Finapres apparatus. Systolic, mean and diastolic blood pressure and heart frequency were recorded during the different tests. Cardiovascular reactivity does not only differ from age group to age group, but also from stressor to stressor. The orthostatic test provided a clear and simple baroreceptor reflex reaction, but the structural changes in the vascular system with an increase in age do have an influence on blood pressure and heart frequency reactivity. A pressure decrease approximately seven seconds after the start of the test is observed almost solely in the case of the younger groups. With the inverted orthostatic test the pressure increase twelve seconds after the start of the test is much more prominent among the younger groups. The results are explained by the greater vascular compliance among the younger

groups. The decreased blood pressure reactivity with an increase in age give rise to a decrease in reflex activity. In the case of the cold pressor test the structural changes in the vascular system also play an important role. The effect of the peripheral constriction is increased by the increased stiffness of the blood vessels. Consequently there is a more rapid and larger increase in blood pressure, and particularly systolic pressure, with an increase in age. Blood pressure and heart frequency decrease with an increase in age when the word-colour conflict test is applied, due to the reduced p-adrenergic influence on the cardiovascular system. Structural changes in the vascular system play an important role in cardiovascular reactivity, depending on the stressor which is applied. Each of the various stressors has a different cardiovascular reactivity pattern, which is each influenced in a different way by autonomous and cardiovascular changes with an increase in age. In studying the relationship between hypertension and hyper reactivity the role of age and the nature of the stressor must be taken into account.