title: The cerebrovascular response to lower-body negative pressure vs. head-up tilt.
abstract: Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (-50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBFv) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT (P≤ 0.020). Mean CBFvinitially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller (P≤ 0.029) during LBNP. The reduction in end-tidal Pco2partial pressure (PetCO2) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT (P= 0.008). We consider the larger decrease in CBFvduring HUT vs. LBNP attributable to the pronounced reduction in PetCO2and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality.NEW & NOTEWORTHYLower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco2together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stress.
authors.affiliation: Department of Internal Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.|Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Anne-Sophie G T
authors.initials: AG
authors.lastname: Bronzwaer
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Jasper
authors.initials: J
authors.lastname: Verbree
authors.affiliation: Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.|Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Wim J
authors.initials: WJ
authors.lastname: Stok
authors.affiliation: Department of Pathology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands; and.
authors.forename: Mat J A P
authors.initials: MJ
authors.lastname: Daemen
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Mark A
authors.initials: MA
authors.lastname: van Buchem
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Matthias J P
authors.initials: MJ
authors.lastname: van Osch
authors.affiliation: Department of Internal Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands; j.j.vanlieshout@amc.uva.nl.|Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.|Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.|Medical Research Center/Arthritis Research United Kingdom Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom.
authors.forename: Johannes J
authors.initials: JJ
authors.lastname: van Lieshout
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004244:Dizziness / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D006112:Gravitation; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure / Q000379:methods; D008297:Male; D020768:Middle Cerebral Artery / Q000378:metabolism / Q000503:physiopathology*; D011187:Posture / Q000502:physiology*; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: cerebral hemodynamics; gravity; orthostatic stress