title: Influence of cerebrovascular resistance on the dynamic relationship between blood pressure and cerebral blood flow in humans.
abstract: We examined the hypothesis that changes in the cerebrovascular resistance index (CVRi), independent of blood pressure (BP), will influence the dynamic relationship between BP and cerebral blood flow in humans. We altered CVRi with (via controlled hyperventilation) and without [via indomethacin (INDO, 1.2 mg/kg)] changes in PaCO2. Sixteen subjects (12 men, 27 ± 7 yr) were tested on two occasions (INDO and hypocapnia) separated by >48 h. Each test incorporated seated rest (5 min), followed by squat-stand maneuvers to increase BP variability and improve assessment of the pressure-flow dynamics using linear transfer function analysis (TFA). Beat-to-beat BP, middle cerebral artery velocity (MCAv), posterior cerebral artery velocity (PCAv), and end-tidal Pco2 were monitored. Dynamic pressure-flow relations were quantified using TFA between BP and MCAv/PCAv in the very low and low frequencies through the driven squat-stand maneuvers at 0.05 and 0.10 Hz. MCAv and PCAv reductions by INDO and hypocapnia were well matched, and CVRi was comparably elevated (P < 0.001). During the squat-stand maneuvers (0.05 and 0.10 Hz), the point estimates of absolute gain were universally reduced, and phase was increased under both conditions. In addition to an absence of regional differences, our findings indicate that alterations in CVRi independent of PaCO2 can alter cerebral pressure-flow dynamics. These findings are consistent with the concept of CVRi being a key factor that should be considered in the correct interpretation of cerebral pressure-flow dynamics as indexed using TFA metrics.
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada; jonathan.smirl@ubc.ca.
authors.forename: J D
authors.initials: JD
authors.lastname: Smirl
authors.affiliation: Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, Wellington, New Zealand; and.
authors.forename: Y C
authors.initials: YC
authors.lastname: Tzeng
authors.affiliation: Faculty of Medicine, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.
authors.forename: B J
authors.initials: BJ
authors.lastname: Monteleone
authors.affiliation: Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada;
authors.forename: P N
authors.initials: PN
authors.lastname: Ainslie
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*; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000378:metabolism / Q000503:physiopathology; D016857:Hypocapnia / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D020768:Middle Cerebral Artery / Q000378:metabolism / Q000502:physiology / Q000503:physiopathology; D020769:Posterior Cerebral Artery / Q000378:metabolism / Q000502:physiology / Q000503:physiopathology
chemical_list: D002245:Carbon Dioxide
keywords: carbon dioxide; cerebral blood flow; cerebral hemodynamics; physiology; resistance; transcranial doppler; transfer function analysis
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