title: Static autoregulation in humans: a review and reanalysis.
abstract: BACKGROUND
  Cerebral autoregulation (CA) is a theoretical construct characterized by the relationship between mean arterial pressure (MAP) and cerebral blood flow (CBF). We performed a comprehensive literature search to provide an up-to-date review on the static relationship between MAP and CBF.
  
  
  METHODS
  The results are based on 40 studies (49 individual experimental protocols) in healthy subjects between 18 and 65 years. Exclusion criteria were: a ΔMAP <5%, hypoxia/hyperoxia or hypo/hypercapnia, and unstable levels (<2 min stages). The partial pressure of arterial CO2 (PaCO2) was measured in a subset of the included studies (n=28); therefore, CBF was also adjusted to account for small changes in PaCO2.
  
  
  RESULTS
  The linear regression coefficient between MAP and CBF (or velocity) of 0.82±0.77%ΔCBF/%ΔMAP during decreases in MAP (n=23 experiments) was significantly different than the relationship of 0.21±0.47%ΔCBF/%ΔMAP during increases (n=26 experiments; p<0.001). After correction for increases/decreases in PaCO2, the slopes were not significantly different: 0.64±1.16%ΔCBF/%ΔMAP (n=16) and 0.39±0.30%ΔCBF/%ΔMAP (n=12) for increased vs. decreased MAP changes, respectively (p=0.60).
  
  
  CONCLUSIONS
  The autoregulatory ability of the cerebral circulation appears to be more active in buffering increases in MAP as compared to reductions in MAP. However, the statistical finding of hysteresis is lost following an attempt to correct for PaCO2.
authors.affiliation: Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands. Electronic address: tiannenuman@gmail.com.
authors.forename: Tianne
authors.initials: T
authors.lastname: Numan
authors.affiliation: Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Canada.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Bain
authors.affiliation: Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Canada.
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Hoiland
authors.affiliation: Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Canada.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Smirl
authors.affiliation: Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Canada.
authors.forename: Nia C
authors.initials: NC
authors.lastname: Lewis
authors.affiliation: Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Canada. Electronic address: philip.ainslie@ubc.ca.
authors.forename: Philip N
authors.initials: PN
authors.lastname: Ainslie
mesh_terms: D062186:Arterial Pressure; D002245:Carbon Dioxide / Q000378:metabolism; D002560:Cerebrovascular Circulation; D006706:Homeostasis; D006801:Humans
chemical_list: D002245:Carbon Dioxide
keywords: Blood pressure; Cerebral autoregulation; Cerebral blood flow; Cerebrovascular CO(2) reactivity