title: Oscillatory cerebral hemodynamics--the macro- vs. microvascular level.
abstract: The phase shift between oscillations of blood pressure (BP) and Doppler middle cerebral artery flow velocity (MCAFV) reflects continuous cerebral autoregulatory action. It is not known whether a similar phase shift exists for cortical hemodynamics ('microvascular level') assessed by near infrared spectroscopy (NIRS) and what the effects are of pathological conditions. This study investigates the phase relations between oscillations of BP, MCAFV and NIRS parameters in 38 healthy older adults and 28 patients with unilateral severe obstructive carotid disease. BP was recorded noninvasively by finger plethysmography. Stable 0.1 Hz oscillations of all hemodynamic parameters were induced by regular breathing at a rate of 6/min. Basic results were that: (1) BP-induced cortical microvascular oscillations (NIRS) follow those of macrovascular oscillations (MCAFV) with a phase of 80-90 degrees (corresponding to 2-2.5 s at 0.1 Hz), most likely reflecting a transit time phenomenon; (2) oxy- and deoxyhemoglobin thereby oscillate in counterphase; (3) hemodynamic compromise in carotid obstruction leads to (a) delayed NIRS oscillations in comparison to BP which are highly correlated to a shorter phase lead of MCAFV against BP and (b) a decoupling of the oxy-/deoxyhemoglobin counterphase to 240 degrees . Cortical hemodynamic responses to BP oscillations follow specific phase relationships due to cerebral autoregulatory action and circulatory transit times. With hemodynamic impairment, as in unilateral carotid obstruction, these phases are significantly changed reflecting disturbed autoregulation.
authors.affiliation: Department of Neurology and Clinical Neurophysiology, University of Freiburg, Neurocenter, Breisacherstr. 64, D-79106 Freiburg, Germany. reinhard@nz.ukl.uni-freiburg.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Reinhard
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Wehrle-Wieland
authors.forename: Daniel
authors.initials: D
authors.lastname: Grabiak
authors.forename: Markus
authors.initials: M
authors.lastname: Roth
authors.forename: Brigitte
authors.initials: B
authors.lastname: Guschlbauer
authors.forename: Jens
authors.initials: J
authors.lastname: Timmer
authors.forename: Cornelius
authors.initials: C
authors.lastname: Weiller
authors.forename: Andreas
authors.initials: A
authors.lastname: Hetzel
mesh_terms: D000368:Aged; D001683:Biological Clocks / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D016893:Carotid Stenosis / Q000000981:diagnostic imaging / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging / Q000503:physiopathology; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000379:methods; D008297:Male; D008833:Microcirculation / Q000000981:diagnostic imaging / Q000502:physiology*; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D010991:Plethysmography; D011237:Predictive Value of Tests; D012307:Risk Factors; D013687:Telencephalon / Q000098:blood supply* / Q000000981:diagnostic imaging / Q000502:physiology; D014463:Ultrasonography