THE DIAGNOSIS AND TREATMENT OF BAROREFLEX FAILURE

Background. Baroreflexes originate in the great vessels of the neck an d thorax and prevent arterial pressure from rising or failing excessiv ely. Methods. This study was undertaken to clarify the cause, clinical spectrum, and therapy of this disorder. We studied 11 patients with b aroreflex failure presenting as severe, labile hypertension and hypote nsion, often with headache, diaphoresis, and emotional instability, an d characterized by the failure of exogenous vasoactive substances to a lter heart rate. Each underwent hemodynamic monitoring and biochemical , physiologic, and pharmacologic testing. Results. The patients' maxim al systolic blood pressures ranged from 164 to 280 mm Hg, and their mi nimal systolic pressures ranged from 58 to 96 mm Hg. Plasma norepineph rine and epinephrine concentrations were sometimes many times normal d uring blood-pressure surges. All the patients had excessive pressor an d tachycardic responses to the mental-arithmetic and cold pressor test s and marked hypersensitivity to clonidine. The underlying causes of b aroreflex failure included the familial paraganglioma syndrome, neck s urgery or radiation therapy for pharyngeal carcinoma, bilateral lesion s of the nucleus tractus solitarii, and surgical section of the glosso pharyngeal nerves; in two patients the cause was unknown. Therapy with clonidine reduced the frequency of attacks by 81 percent and attenuat ed the elevated blood pressure and heart rate in the attacks that occu rred. Conclusions. The syndrome of baroreflex failure should be consid ered in patients with otherwise unexplained labile hypertension. Cloni dine attenuates the pressor and tachycardic surges in baroreflex failu re.