Heterogeneous patterns of vasoreactivity in the middle cerebral and internal carotid arteries.
This study compared changes in cross-sectional area (CSA) and flow (Q) between the middle cerebral artery (MCA) and the internal carotid artery (ICA) at baseline and during 5 min of hypercapnia (HC; 6% CO2) and hypocapnia (HO; hyperventilation) and quantified how these changes contribute to estimates of cerebrovascular reactivity (CVR). Measures of MCA CSA were made using 3T magnetic resonance imaging. On a separate day, MCA flow velocity was measured with transcranial Doppler ultrasound and ICA diameters and flow velocity were measured with duplex ultrasound. Fourteen subjects (23 ± 3 yr, 7 females) participated, providing data for 11 subjects during HC and 9 subjects during HO. An increase in MCA CSA (P < 0.05) was observed within the first minute of HC. During HO, the decrease in MCA CSA (P < 0.05) was delayed until minute 4. No changes were observed in ICA CSA during HC or HO. The relative changes in QICA and QMCA were similar during HC and HO. Therefore, the MCA, but not ICA, dilates and constricts during 5 min of HC and HO, respectively. The consequent impact on QMCA significantly affects estimates of CVR, and reactivity cannot be attributed solely to changes in smaller arterioles.
Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada; and.
Nicole S
NS
Coverdale
Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada; and.
Sophie
S
Lalande
Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada; and.
Amanda
A
Perrotta
Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada; and Department of Physiology and Pharmacology, Western University, London, Ontario, Canada kshoemak@uwo.ca.
J Kevin
JK
Shoemaker
D000222:Adaptation, Physiological; D000328:Adult; D001783:Blood Flow Velocity; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016857:Hypocapnia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D012039:Regional Blood Flow; D013997:Time Factors; D018616:Ultrasonography, Doppler, Duplex; D018617:Ultrasonography, Doppler, Pulsed; D017585:Ultrasonography, Doppler, Transcranial; D014661:Vasoconstriction; D014664:Vasodilation; D055815:Young Adult
cerebrovascular reactivity; internal carotid artery; magnetic resonance imaging; middle cerebral artery; transcranial Doppler ultrasound