title: Evaluation of cerebrovascular impedance and wave reflection in mouse by ultrasound.
abstract: Genetic and surgical mouse models are commonly used to study cerebrovascular disease, but their size makes invasive hemodynamic testing technically challenging. The purpose of this study was to demonstrate a noninvasive measurement of cerebrovascular impedance and wave reflection in mice using high-frequency ultrasound in the left common carotid artery (LCCA), and to examine whether microvascular changes associated with hypercapnia could be detected with such an approach. Ten mice (C57BL/6J) were studied using a high-frequency ultrasound system (40 MHz). Lumen area and blood flow waveforms were obtained from the LCCA and used to calculate pulse-wave velocity, input impedance, and reflection amplitude and transit time under both normocapnic and hypercapnic (5% CO2) ventilation. With hypercapnia, vascular resistance was observed to decrease by 87%±12%. Although the modulus of input impedance was unchanged with hypercapnia, a phase decrease indicative of increased total arterial compliance was observed at low harmonics together with an increased reflection coefficient in both the time (0.57±0.08 versus 0.68±0.08, P=0.04) and frequency domains (0.62±0.08 versus 0.73±0.06, P=0.02). Interestingly, the majority of LCCA blood flow was found to pass into the internal carotid artery (range=76% to 90%, N=3), suggesting that hemodynamic measurements in this vessel are a good metric for intracerebral reactivity in mouse.
authors.affiliation: 1] Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada [2] Division of Physiology and Experimental Medicine, Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Macgowan
authors.affiliation: Division of Physiology and Experimental Medicine, Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada.
authors.forename: Sarah Joy
authors.initials: SJ
authors.lastname: Stoops
authors.affiliation: Mouse Imaging Centre, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada.
authors.forename: Yu-Qing
authors.initials: YQ
authors.lastname: Zhou
authors.affiliation: Mouse Imaging Centre, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada.
authors.forename: Lindsay S
authors.initials: LS
authors.lastname: Cahill
authors.affiliation: 1] Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada [2] Mouse Imaging Centre, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, Toronto, Ontario, Canada.
authors.forename: John G
authors.initials: JG
authors.lastname: Sled
mesh_terms: D000818:Animals; D017536:Carotid Artery, Common / Q000000981:diagnostic imaging*; D002560:Cerebrovascular Circulation / Q000502:physiology; D017097:Electric Impedance; D006439:Hemodynamics; D006935:Hypercapnia / Q000503:physiopathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D014463:Ultrasonography; D014655:Vascular Resistance / Q000502:physiology