A comparison of cardiovascular responses in reactive and non-reactive individuals to psychological and physical challenge

The difficulty encountered in attempts to induce a permanent hypertension in animals with psychologically stressful paradigms has lead many investigators to doubt the importance of the contributions of psychological stress to hypertension. However, recent evidence indicates that selective breeding can produce an animal which will develop hypertension when exposed to chronic stress. This finding has contributed to a renewed interest in individual differences which might produce a vulnerability to stress-induced hypertension. A cardiovascular system which is highly responsive to stress may be one manifestation of such a vulnerability. The pathogenic potential of a cardiovascular system that is reactive only in one situation is probably limited. For cardiovascular reactivity to have significance in the etiology of hypertension it must be demonstrable in a variety of situations. This study was undertaken in an effort to demonstrate the generality of cardiovascular reactivity and to obtain basic information about the cardiovascular and oxygen uptake capacities of individuals who differ in reactivity to stress.

Thirty-four male undergraduate volunteers were exposed to three forms of psychological challenge: l) a reaction time-shock avoidance task (RT-AV); 2) a reaction time-money reward condition (appetitive or RT-AP); and 3) a mental arithmetic stress (MA). Heart rate, systolic and diastolic blood pressure and urinary excretion of epinephrine and norepinephrine were measured. The primary focus of the study was on those individuals showing extremes in cardiovascular reactivity during RT-AV. Eight subjects showing a heart rate increase of over 30 bpm were compared to six subjects who responded with less than a l0 bpm increase to the RT-AV task. A comparison of these two groups in the other conditions found that the reactive group displayed a greater change in heart rate to the RT-AP task but not the MA condition. Systolic blood pressures of the reactives while not different at rest, were higher during the RT-AV, RT-AP and MA conditions. No difference in urinary excretion of catecholamines between the two groups was detected but significant positive correlations between baseline epinephrine values and resting heart rate and mean heart rate change in all psychological conditions were found. A significant relationship between cardiovascular reactivity and familial hypertension was also found.

The reactive and non-reactive groups did not differ in aerobic capacity or maximum heart rate and both met the metabolic demands of exercise with similar rises in cardiovascular parameter.. There was evidence that as a group the reactive subjects showed higher heart rates and systolic blood pressures than the non-reactive group to the same relative and absolute workloads. The results are discussed in respect to the contribution of cardiovascular reactivity in producing a vulnerability to hypertension.