Classical conditioning of vascular responses in mild hypertensives and normotensives

Using a discriminative classical conditioning paradigm, this study addresses the question of whether vascular responses are more easily acquired or slower to extinguish in mild hypertensives than in normotensive controls. We subjected 18 mild hypertensives, with a resting systolic/diastolic blood pressure of 141/100 mmHg, and 17 normotensive controls similar in age, with resting systolic/diastolic blood pressure 122/80 mmHg, to a discriminative Pavlovian conditioning paradigm with tones of 8 s duration serving as conditioned stimuli (CS) and a mild electric shock as an unconditioned stimulus (UCS). Digital finger pulse volume (FPV) responses were recorded during an acquisition phase, where CS+, but not CS-, was repeatedly paired with the UCS (12 trials), and an extinction phase where shocks were withheld (12 trials). During the acquisition phase, mild hypertensives displayed greater anticipatory vasoconstrictive responses both to CS+ and CS- compared with normotensive controls. In addition, unconditioned FPV responses were enhanced in mild hypertensives. During the extinction phase, mild hypertensives evidenced increased resistance to extinction since conditioned vasoconstriction was more frequently observed in response to CS+ than to CS- in mild hypertensives only. Thus, vascular dysregulation in mild hypertensives was evident both for unconditioned and conditioned vasoconstriction. Data are compatible both with a centrally determined increased conditionability in mild hypertensive compared with normotensive and with a decreased threshold for peripheral vascular responsiveness among mild hypertensives.