Baroreflex buffering and susceptibility to vasoactive drugs

Background— The overall effect of vasoactive drugs on blood pressure is determined by a combination of the direct effect on vascular tone and an indirect baroreflex-mediated effect, a baroreflex buffering of blood pressure. Differences in baroreflex function affect the responsiveness to vasoactive medications, particularly baroreflex buffering of blood pressure; however, the magnitude is not known. Methods and Results— We characterized baroreflex function and responses to vasoactive drugs in patients with idiopathic orthostatic intolerance, patients with essential hypertension, patients with monogenic hypertension and brachydactyly, patients with multiple system atrophy, and control subjects. We used phenylephrine sensitivity during ganglionic blockade as a measure of baroreflex buffering. Phenylephrine (25 μg) increased systolic blood pressure 6±1.6 mm Hg in control subjects, 6±1.1 mm Hg in orthostatic intolerance patients, 18±3.9 mm Hg in patients with essential hypertension, 31±3.4 mm Hg in patients wi...