Circulatory and catecholamine changes during head-up tilt testing in neurocardiogenic (vasovagal) syncope.

Changes in heart rate, arterial pressure, norepinephrine and epinephrine levels were compared in 19 consecutive patients (10 men and 9 women, mean age 46 +/- 16 years) with neurocardiogenic syncope and 11 age- and sex-matched control subjects (5 men and 6 women, mean age 49 +/- 15 years) during head-up tilt testing. Norepinephrine and epinephrine levels were measured at the baseline supine position, in the initial upright position, every 90 seconds during the 70 degrees upright tilt, at the time of termination due to hypotension and syncope (or at 15 minutes in control subjects), and at 40 seconds and 1 minute and 40 seconds in the supine position after terminating the head-up tilt test. Baseline norepinephrine, epinephrine and heart rate were slightly higher in patients. Despite a significant decrease in mean arterial pressure during head-up tilt testing in patients (51 +/- 20 mm Hg; p < 0.001), norepinephrine levels in patients and control subjects at the time of terminating the head-up tilt test were comparable (459 +/- 204 vs 473 +/- 172 pg/ml). A fivefold increase in epinephrine levels (73 +/- 53 to 345 +/- 260 pg/ml; p < 0.01) were seen in patients, whereas control subjects had insignificant change (38 +/- 16 to 65 +/- 44 pg/ml). It is concluded that diminished neuronal sympathetic activity and enhanced adrenomedullary activity is demonstrated during head-up tilt testing in patients with neurocardiogenic syncope.