title: Postural effects on cerebral blood flow and autoregulation.
abstract: Cerebral autoregulation (CA) is thought to maintain relatively constant cerebral blood flow (CBF) across normal blood pressures. To determine if postural changes alter CA, we measured cerebral blood flow velocity (CBFv) in the middle cerebral arteries, mean arterial blood pressure (MABP), cardiac output (Q), and end-tidal carbon dioxide (PETCO2) in 18 healthy individuals (11 female and seven male; 26 ± 9 years) during repeated periods of supine and seated rest. Multiple regression was used to evaluate the influence of PETCO2, MABP, Q, and hydrostatic pressure on CBFv. Static CA was assessed by evaluating absolute changes in steady-state CBFv. Dynamic CA was assessed by transfer function analysis of the CBFv response to spontaneous oscillations in MABP In the seated versus supine posture, MABP (67.2 ± 7.2 vs. 84.2 ± 12.1 mmHg;P< 0.001), CBFv (55.2 ± 9.1 vs. 63.6 ± 10.6 cm/sec;P< 0.001) and PETCO2(29.1 ± 2.6 vs. 30.9 ± 2.3 mmHg;P< 0.001) were reduced. Changes in CBFv were not explained by variance in PETCO2, MABP, Q, or hydrostatic pressure. A reduction in MABP to CBFv transfer function gain while seated (P< 0.01) was explained by changes in the power spectrum of MABP, not CBFv. Our findings suggest that changes in steady-state cerebral hemodynamics between postures do not appear to have a large functional consequence on the dynamic regulation of CBF.
authors.affiliation: Department of Biology, University of Colorado Colorado Springs, Colorado Springs, Colorado.
authors.forename: Zachary K
authors.initials: ZK
authors.lastname: Garrett
authors.affiliation: Department of Biology, University of Colorado Colorado Springs, Colorado Springs, Colorado.
authors.forename: James
authors.initials: J
authors.lastname: Pearson
authors.affiliation: Department of Biology, University of Colorado Colorado Springs, Colorado Springs, Colorado asubudhi@uccs.edu.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Subudhi
mesh_terms: D000293:Adolescent; D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D055815:Young Adult
keywords: Cardiac output; cerebrovascular; end‐tidal carbon dioxide; hydrostatic pressure; seated; supine