Transcranial Doppler Studies on Cerebral Autoregulation Suggest Prolonged Cerebral Vasoconstriction in a Subgroup of Patients with Orthostatic Intolerance

We studied the cerebral autoregulation in a subgroup of patients with orthostatic intolerance, who exhibited excessively decreased middle cerebral artery flow velocity (MCAFV) on transcranial Doppler sonography (TCD) during head-up tilt (HUT) test but without orthostatic hypotension or postural tachycardia. Twenty patients and 20 age- and sex-matched controls underwent Valsalva maneuver (VM) and HUT test with simultaneous monitoring of MCAFV by TCD and blood pressure, heart rate recordings. The pulsatility index (PI), cerebrovascular resistance (CVR) and autoregulatory indices were calculated. During HUT, patients had marked MCAFV reduction (-29.0 ± 5.25% vs. -8.01 ± 4.37%), paradoxically decreased PI (0.68 ± 0.17 vs. 0.96 ± 0.28) but increased CVR (45.7 ± 16.7% vs. 14.3 ± 12.6%). The MCAFV decreased similarly during early phase II of VM in both groups but did not recover to baseline in patients during late phase II, phase III and less overshoot in phase IV (-11 ± 16.7% vs. +2.2 ± 17.9 %; -15.4 ± 16.5% vs. -2.4 ± 17.8% and 16.7 ± 22.9% vs. 38.7 ± 26.5%, respectively). We concluded that in these patients, cerebrovascular vasoconstriction in response to physiologic stimulation was normal but relaxation during and after stimulation were impaired, indicating prolonged cerebral vasoconstriction.