title: Investigation of cerebral haemodynamics by near-infrared spectroscopy in young healthy volunteers reveals posture-dependent spontaneous oscillations.
abstract: Autonomic reflexes enable the cardiovascular system to respond to gravitational displacement of blood during changes in posture. Spontaneous oscillations present in the cerebral and systemic circulation of healthy subjects have demonstrated a regulatory role. This study assessed the dynamic responses of the cerebral and systemic circulation upon standing up and the posture dependence of spontaneous oscillations. In ten young healthy volunteers, blood pressure and cerebral haemodynamics were continuously monitored non-invasively using the Portapres and near-infrared spectroscopy (NIRS), respectively. Oscillatory changes in the cerebral NIRS signals and the diastolic blood pressure (DBP) signal have been identified by the fast Fourier analysis. Blood pressure increased during standing and returned to basal level when volunteers sat on a chair. The mean value of cerebral tissue oxygen index (TOI) as measured by NIRS did not demonstrate any significant changes. Oscillatory changes in DBP, oxyhaemoglobin concentration [O2Hb] and TOI showed a significant increase when subjects were standing. Investigation of the low frequency component (approximately 0.1 Hz) of these fluctuations revealed posture dependence associated with activation of autonomic reflexes. Systemic and cerebral changes appeared to preserve adequate blood flow and cerebral perfusion during standing in healthy volunteers. Oscillatory changes in [O2Hb] and TOI, which may be related to the degree of cerebral sympathetic stimulation, are posture dependent in healthy subjects.
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, London WC1E 6JA, UK. iliastac@medphys.ucl.ac.uk
authors.forename: Ilias
authors.initials: I
authors.lastname: Tachtsidis
authors.forename: Clare E
authors.initials: CE
authors.lastname: Elwell
authors.forename: Terence S
authors.initials: TS
authors.lastname: Leung
authors.forename: Chuen-Wai
authors.initials: CW
authors.lastname: Lee
authors.forename: Martin
authors.initials: M
authors.lastname: Smith
authors.forename: David T
authors.initials: DT
authors.lastname: Delpy
mesh_terms: D000293:Adolescent; D000328:Adult; D001683:Biological Clocks / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*