OBJECTIVE:To investigate the prevalence,symptoms,and neurophysiologic features of delayed orthostatic hypotension(OH).METHODS:Blood pressures(BP)were measured at 1minute intervals on 230 patients during 60°head-up tilt for 45 minutes and standing for 5 minutes.OH was defined as a sustained fall in BP(≥20 mm Hg systolic or ≥10 mm Hg diastolic)and delayed OH as a sustained BP fall occurring beyond 3 minutes of standing or upright tilt table testing.Beat-to-beat BP,tests of cardiovagal function,and sympathetic-adrenergic function were performed.RESULTS:Of patients with OH,only 46%had OH within 3 minutes of head up tilt;15%had OH between 3 and 10 minutes;and 39%had OH only after 10 minutes of tilt table testing.The magnitude and the temporal distribution of the BP fall did not differ between those with and without symptoms of orthostatic intolerance.Patients with OH beyond 10 minutes tended to be younger(p < 0.05),have smaller BP falls during phase II of the Valsalva maneuver(p <.0.01),and have greater phase IV overshoot(p < 0.01).CONCLUSIONS:Delayed orthostatic hypotension occurred in 54%of our tested population and was associated with milder abnormalities of sympathetic adrenergic function,suggesting this disorder may be a mild or early form of sympathetic adrenergic failure. OBJECTIVE: To investigate the prevalence, symptoms, and neurophysiologic features of delayed orthostatic hypotension (OH) .METHODS: Blood pressures (BP) were measured at 1minute intervals on 230 patients during 60 ° head-up tilt for 45 minutes and standing for 5 minutes .OH was defined as a sustained fall in BP (≥20 mm Hg systolic or ≥10 mm Hg diastolic) and delayed OH as a sustained BP fall later than 3 minutes of standing or upright tilt table testing. Beat-to-beat BP, tests of cardiovagal function, and sympathetic-adrenergic function were performed .RESULTS: Of patients with OH, only 46% had OH within 3 minutes of head up tilt; 15% had OH between 3 and 10 minutes; and 39% had OH only after 10 minutes of tilt table testing. Magnitude and the temporal distribution of the BP fall did not differ between those with and without symptoms of orthostatic intolerance. Patients with OH beyond 10 minutes tended to be younger (p <0.05), have smaller BP falls during phase II of the Valsalva maneuver (p <.0.01 ), and have greater phase IV overshoot (p <0.01) .CONCLUSIONS: Delayed orthostatic hypotension occurred in 54% of our tested patient population and was associated with milder abnormalities of sympathetic adrenergic function, suggesting this disorder may be a mild or early form of sympathetic adrenergic failure.