title: Cerebral blood flow velocity underestimates cerebral blood flow during modest hypercapnia and hypocapnia.
abstract: To establish the accuracy of transcranial Doppler ultrasound (TCD) measures of middle cerebral artery (MCA) cerebral blood flow velocity (CBFV) as a surrogate of cerebral blood flow (CBF) during hypercapnia (HC) and hypocapnia (HO), we examined whether the cross-sectional area (CSA) of the MCA changed during HC or HO and whether TCD-based estimates of CBFV were equivalent to estimates from phase contrast (PC) magnetic resonance imaging. MCA CSA was measured from 3T magnetic resonance images during baseline, HO (hyperventilation at 30 breaths/min), and HC (6% carbon dioxide). PC and TCD measures of CBFV were measured during these protocols on separate days. CSA and TCD CBFV were used to calculate CBF. During HC, CSA increased from 5.6 ± 0.8 to 6.5 ± 1.0 mm(2) (P < 0.001, n = 13), while end-tidal carbon dioxide partial pressure (PETCO2) increased from 37 ± 3 to 46 ± 5 Torr (P < 0.001). During HO, CSA decreased from 5.8 ± 0.9 to 5.3 ± 0.9 mm(2) (P < 0.001, n = 15), while PetCO2 decreased from 36 ± 4 to 23 ± 3 Torr (P < 0.001). CBFVs during baseline, HO, and HC were compared between PC and TCD, and the intraclass correlation coefficient was 0.83 (P < 0.001). The relative increase from baseline was 18 ± 8% greater (P < 0.001) for CBF than TCD CBFV during HC, and the relative decrease of CBF during HO was 7 ± 4% greater than the change in TCD CBFV (P < 0.001). These findings challenge the assumption that the CSA of the MCA does not change over modest changes in PETCO2.
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada;
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Coverdale
authors.affiliation: Robarts Research Institute, Western University, London, Ontario, Canada; and.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Gati
authors.affiliation: Robarts Research Institute, Western University, London, Ontario, Canada; and.
authors.forename: Oksana
authors.initials: O
authors.lastname: Opalevych
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada;
authors.forename: Amanda
authors.initials: A
authors.lastname: Perrotta
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada; Department of Physiology and Pharmacology, Western University, London, Ontario, Canada kshoemak@uwo.ca.
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000097:blood*; D002533:Cerebral Angiography / Q000379:methods* / Q000592:standards; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016857:Hypocapnia / Q000097:blood / Q000000981:diagnostic imaging / Q000503:physiopathology*; D018810:Magnetic Resonance Angiography / Q000592:standards; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology*; D010313:Partial Pressure; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D017585:Ultrasonography, Doppler, Transcranial / Q000592:standards; D014661:Vasoconstriction; D014664:Vasodilation; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: cerebral blood flow velocity; magnetic resonance imaging; middle cerebral artery; transcranial Doppler ultrasound