Cerebral blood flow and end-tidal CO 2 predict lightheadedness during head-up tilt in patients with orthostatic intolerance

Orthostatic intolerance (OI) is a common problem. Reliable markers of OI are missing, as orthostatic blood pressure and heart rate poorly correlate with orthostatic symptoms. The objective of this study was to assess the relationship between orthostatic lightheadedness and cerebral blood flow. In this retrospective study patients with OI were evaluated at the Autonomic Laboratory of the Department of Neurology, Brigham and Women's Faulkner Hospital, Boston. The 10-minute head-up tilt test was performed as a part of autonomic testing. Orthostatic lightheadedness was evaluated at every minute of the head-up tilt. Heart rate, blood pressure, capnography, and cerebral blood flow velocity (CBFv) in the middle cerebral artery using transcranial Doppler were measured. Repeated-measures design with a linear mixed-effects model was used to evaluate the relationship between orthostatic lightheadedness and hemodynamic variables. Correlation analyses were done by calculating Pearson's coefficient. Twenty-two patients with OI were compared to nineteen controls. Orthostatic CBFv and end-tidal CO decreased in OI patients compared to controls (p