EPISODIC HYPERTENSION ASSOCIATED WITH SITTING ON HARD SURFACES. R.M. Witteles 1 ; 1 Stanford University, Stanford, CA LEARNING OBJECTIVES: 1. Distinguish between the potential causes of episodic hypertension. 2. Recognize the practical consequences of the complex relationship between pain and elevated blood pressure. CASE INFORMATION: A 76-year-old Japanese-American male was referred to the hypertension clinic for a long-standing history of baseline normotension interrupted by hypertensive episodes associated only with sitting on hard surfaces. Home blood pressure measurements (consistent with measurements in clinic) ranged between 110 ± 120/70 ± 80 mm Hg, but rose to 180 ± 190/100 ± 110 mm Hg immediately after the patient sat on a hard surface such as an ordinary chair; no change in blood pressure from normal values was observed when the patient sat on a soft surface or was in any other position. Measured blood pressure was the same in both arms, and returned to a normal range immediately after the patient stopped sitting on a hard surface. The patient experienced no symptoms when sitting on a hard surface except for bilateral blurry vision; this too promptly returned to normal after getting up from the hard surface. At various times in his life, the patient had taken reserpine, lisinopril, verapamil, enalapril, atenolol, hydrochlorothiazide, and clonidine to control his hypertensive episodes, always without efficacy; he is currently taking no anti-hypertensive medications. Of possible relevance, the patient had chronic neck pain which was exacerbated by sitting on hard surfaces; however, the change in blood pressure reliably and reproducibly occurred before the pain. The patient had normal urinary catecholamines, vanillylmandelic acid, and metanephrine values, normal thyroid studies, no evidence of panic disorder, and no evidence of end-organ damage. A trial of opioid analgesics had no effect on the patient's blood pressure. DISCUSSION: Episodic hypertension is a relatively uncommon clinical entity, most often associated with the "white-coat" phenomenon, pheochromocytoma, ingestion of sympathomimetic drugs, withdrawal from alcohol and other drugs, thyrotoxicosis, panic disorder, and intermittent pain. Prior studies have discovered a complex relationship between pain and blood pressure, with involvement at multiple areas of the central nervous system. This patient demonstrated an unusual temporal relationship between pain and blood pressure, with the rise in blood pressure occurring first; the hypothesis of a conditioned response should be considered.