title: Impaired Cerebral Autoregulation during Head Up Tilt in Patients with Severe Brain Injury.
abstract: Early mobilization is of importance for improving long-term outcome for patients after severe acquired brain injury. A limiting factor for early mobilization by head-up tilt is orthostatic intolerance. The purpose of the present study was to examine cerebral autoregulation in patients with severe acquired brain injury and a low level of consciousness. Fourteen patients with severe acquired brain injury and orthostatic intolerance and fifteen healthy volunteers were enrolled. Blood pressure was evaluated by pulse contour analysis, heart rate and RR-intervals were determined by electrocardiography, middle cerebral artery velocity was evaluated by transcranial Doppler, and near-infrared spectroscopy determined frontal lobe oxygenation in the supine position and during head-up tilt. Cerebral autoregulation was evaluated as the mean flow index calculated as the ratio between middle cerebral artery mean velocity and estimated cerebral perfusion pressure. Patients with acquired brain injury presented an increase in mean flow index during head-up tilt indicating impaired autoregulation (P < 0.001). Spectral analysis of heart rate variability in the frequency domain revealed lower magnitudes of ~0.1 Hz spectral power in patients compared to healthy controls suggesting baroreflex dysfunction. In conclusion, patients with severe acquired brain injury and orthostatic intolerance during head-up tilt have impaired cerebral autoregulation more than one month after brain injury.
authors.affiliation: Research Unit on Brain Injury Neuro Rehabilitation Copenhagen, Department of Neurorehabilitation/ TBI Unit, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Christian Gunge
authors.initials: CG
authors.lastname: Riberholt
authors.affiliation: Department of Anaesthesia, Rigshospitalet, Copenhagen, Denmark.|Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Niels Damkjær
authors.initials: ND
authors.lastname: Olesen
authors.affiliation: Department of Paediatrics, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark.
authors.forename: Mira
authors.initials: M
authors.lastname: Thing
authors.affiliation: Research Unit for Musculoskeletal Function and Physiotherapy, Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.|Department of Rehabilitation, Copenhagen University Hospital Herlev and Gentofte, Gentofte, Denmark.
authors.forename: Carsten Bogh
authors.initials: CB
authors.lastname: Juhl
authors.affiliation: Coordinating Research Centre, Bispebjerg & Frederiksberg Hospital, Frederiksberg, Denmark.
authors.forename: Jesper
authors.initials: J
authors.lastname: Mehlsen
authors.affiliation: Research Unit on Brain Injury Neuro Rehabilitation Copenhagen, Department of Neurorehabilitation/ TBI Unit, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Tue Hvass
authors.initials: TH
authors.lastname: Petersen
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000503:physiopathology*; D001930:Brain Injuries / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D004562:Electrocardiography; D005260:Female; D006439:Hemodynamics; D006706:Homeostasis; D006801:Humans; D008297:Male; D008875:Middle Aged; D018667:Tilt-Table Test