Spontaneous fluctuations in cerebral blood flow regulation: contribution of PaCO2.
To investigate the temporal variability of dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow to rapid changes in arterial blood pressure, a new approach was introduced to improve the temporal resolution of dynamic CA assessment. Continuous bilateral recordings of cerebral blood flow velocity (transcranial Doppler, middle cerebral artery), end-tidal Pco(2) (Pet(CO(2)), infrared capnograph), and blood pressure (Finapres) were obtained at rest and during breath hold in 30 young subjects (25 ± 6 yr old) and 30 older subjects (64 ± 4 yr old). Time-varying estimates of the autoregulation index [ARI(t)] were obtained with an autoregressive-moving average model with coefficients expanded by orthogonal decomposition. The temporal pattern of ARI(t) varied inversely with Pet(CO(2)), decreasing with hypercapnia. At rest, ARI(t) showed spontaneous fluctuations that were significantly different from noise and significantly correlated with spontaneous fluctuations in Pet(CO(2)) in the majority of recordings (young: 72% and old: 65%). No significant differences were found in ARI(t) due to aging. This new approach to improve the temporal resolution of dynamic CA parameters allows the identification of physiologically meaningful fluctuations in dynamic CA efficiency at rest and in response to changes in arterial CO(2).
Panerai
R B
RB
Medical Physics Group, Department of Cardiovascular Sciences, University of Leicester National Health Service Trust, Leicester, UK. rp9@le.ac.uk
Dineen
N E
NE
Brodie
F G
FG
Robinson
T G
TG
D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging; D001783:Blood Flow Velocity; D001794:Blood Pressure; D019296:Capnography; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation; D006339:Heart Rate; D006706:Homeostasis; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D056152:Respiratory Rate; D013997:Time Factors; D017585:Ultrasonography, Doppler, Transcranial; D014655:Vascular Resistance; D055815:Young Adult
D002245:Carbon Dioxide