title: Wave intensity analysis from the common carotid artery: a new noninvasive index of cerebral vasomotor tone.
abstract: Cerebral vasomotor tone is difficult to assess in patients. Wave intensity analysis has been applied to resolve complex upstream and downstream events within the vascular system. We hypothesized that the backward-traveling wave measured in the common carotid artery was caused by reflection from the cerebrovascular "beach", and that the magnitude of this reflected wave would be altered by changes in cerebral vasomotor tone. We measured common carotid arterial diameter and velocity of flow to calculate wave intensity in ten healthy male volunteers (age mean 31 +/- 3 years). Applying a rebreathing technique, we were able to increase the inspired carbon dioxide concentration to a mean of 5.9% +/- 1.7% and to compare baseline wave intensity readings to those recorded during hypercapnia. The magnitude of the reflected wave decreased significantly after CO(2) rebreathing, from -43.0 +/- 27.1 to -25.0 +/- 16.9 mmHg m s(-2), P = 0.02. This reduction in negative wave reflections in mid-systole during hypercapnia remained significant when it was analyzed as the reflection coefficient (the magnitude of the reflected wave normalized for the magnitude of the initiating forward wave, which fell from -2.8 +/- 1.5 to -1.6 +/- 1.4 ms (P = 0.01). Carotid wave reflection was significantly decreased during cerebral vasodilatation induced by increased arterial pCO(2). Wave intensity may provide a simple noninvasive means of assessing changes in cerebral vasomotor tone in vivo.
authors.affiliation: Department of Cardiology, Wales Heart Research Institute, Heath Park, Cardiff Cardiff, UK. bleasdalera@cf.ac.uk
authors.forename: Robert A
authors.initials: RA
authors.lastname: Bleasdale
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Mumford
authors.forename: Ross I
authors.initials: RI
authors.lastname: Campbell
authors.forename: Alan G
authors.initials: AG
authors.lastname: Fraser
authors.forename: Christopher J H
authors.initials: CJ
authors.lastname: Jones
authors.forename: Michael P
authors.initials: MP
authors.lastname: Frenneaux
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001795:Blood Pressure Determination / Q000379:methods; D017536:Carotid Artery, Common / Q000502:physiology*; D006801:Humans; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results