title: Assessment of middle cerebral artery diameter during hypocapnia and hypercapnia in humans using ultra-high-field MRI.
abstract: In the evaluation of cerebrovascular CO2 reactivity measurements, it is often assumed that the diameter of the large intracranial arteries insonated by transcranial Doppler remains unaffected by changes in arterial CO2 partial pressure. However, the strong cerebral vasodilatory capacity of CO2 challenges this assumption, suggesting that there should be some changes in diameter, even if very small. Data from previous studies on effects of CO2 on cerebral artery diameter [middle cerebral artery (MCA)] have been inconsistent. In this study, we examined 10 healthy subjects (5 women, 5 men, age 21-30 yr). High-resolution (0.2 mm in-plane) MRI scans at 7 Tesla were used for direct observation of the MCA diameter during hypocapnia, -1 kPa (-7.5 mmHg), normocapnia, 0 kPa (0 mmHg), and two levels of hypercapnia, +1 and +2 kPa (7.5 and 15 mmHg), with respect to baseline. The vessel lumen was manually delineated by two independent observers. The results showed that the MCA diameter increased by 6.8 ± 2.9% in response to 2 kPa end-tidal P(CO2) (PET(CO2)) above baseline. However, no significant changes in diameter were observed at the -1 kPa (-1.2 ± 2.4%), and +1 kPa (+1.4 ± 3.2%) levels relative to normocapnia. The nonlinear response of the MCA diameter to CO2 was fitted as a continuous calibration curve. Cerebral blood flow changes measured by transcranial Doppler could be corrected by this calibration curve using concomitant PET(CO2) measurements. In conclusion, the MCA diameter remains constant during small deviations of the PET(CO2) from normocapnia, but increases at higher PET(CO2) values.
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; j.verbree@lumc.nl.
authors.forename: Jasper
authors.initials: J
authors.lastname: Verbree
authors.affiliation: Laboratory for Clinical Cardiovascular Physiology, Academic Medical Center, Amsterdam, The Netherlands; Department of Internal Medicine, Academic Medical Center, Amsterdam, The Netherlands; and.
authors.forename: Anne-Sophie G T
authors.initials: AS
authors.lastname: Bronzwaer
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands;
authors.forename: Eidrees
authors.initials: E
authors.lastname: Ghariq
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands;
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Versluis
authors.affiliation: Department of Pathology, Academic Medical Center, Amsterdam, The Netherlands;
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 Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands;
authors.forename: Albert
authors.initials: A
authors.lastname: Dahan
authors.affiliation: Laboratory for Clinical Cardiovascular Physiology, Academic Medical Center, Amsterdam, The Netherlands; Department of Internal Medicine, Academic Medical Center, Amsterdam, The Netherlands; and MRC/Arthritis Research UK 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
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands;
authors.forename: Matthias J P
authors.initials: MJ
authors.lastname: van Osch
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002138:Calibration; D002245:Carbon Dioxide / Q000097:blood*; D002533:Cerebral Angiography / Q000379:methods* / Q000592:standards; D002560:Cerebrovascular Circulation; D005260:Female; D064368:Healthy Volunteers; 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*; D008955:Models, Cardiovascular; D017711:Nonlinear Dynamics; D015588:Observer Variation; D010313:Partial Pressure; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D017585:Ultrasonography, Doppler, Transcranial / Q000592:standards; D014664:Vasodilation; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: MRI; angiography; cerebral blood flow measurement; hypercapnia; hypocapnia; transcranial Doppler