Autonomic function in hypertensive patients with neurovascular compressionof the ventrolateral medulla oblongata

Objective To study whether abnormalities of autonomic function exist in pat ients with essential hypertension and neurovascular compression (NVC) of th e medulla oblongata. Subjects and methods We studied 25 untreated patients with essential hypert ension (13 men and 12 women, 27-74 years old), High-resolution magnetic res onance imaging and magnetic resonance angiography were used to detect NVC, Twenty-four-hour ambulatory monitoring of blood pressure and electrocardiog ram were performed, and the power spectrum of heart rate variability was an alyzed. On a separate day, various autonomic activity tests, including ment al stress, hand grip, cold presser, and Valsalva maneuver were performed. B aroreflex sensitivity was calculated from changes of blood pressure and R-R interval during phenylephrine infusion. A clonidine suppression test was a lso performed, with measurement of plasma catecholamine levels. Results Fourteen of 25 patients (56%) had NVC (C group), and 11 patients di d not have NVC (NC group). There were no significant differences in age, se x, family history, or duration of hypertension between the C and NC groups. Average 24-h systolic blood pressure was similar between the two groups, a lthough 24-h diastolic blood pressure was higher in the C group than the NC group. Daytime, night-time, and 24-h heart rate was significantly higher i n the C group than in the NC group. Night-time low frequency/high frequency ratio was slightly higher in the C group. Plasma norepinephrine levels wer e significantly higher (467 +/- 217 versus 299 +/- 122 pg/ml), and baroflex sensitivity was slightly lower in the C group than in the NC group. Respon ses of blood pressure and heart rate to mental stress, cold presser, hand g rip, Valsalva maneuver, phenylephrine infusion, and clonidine tests were no t significantly different between the two groups. Conclusions NVC of the medulla oblongata was frequently found in patients w ith essential hypertension. Patients with NVC appeared to have enhanced sym pathetic nervous activity compared with those without the compression, J Hy pertens 1999, 17:1257-1263 (C) Lippincott Williams & Wilkins.