title: Acute hypoxia impairs dynamic cerebral autoregulation: results from two independent techniques.
abstract: We investigated the effect of acute hypoxia (AH) on dynamic cerebral autoregulation (CA) using two independent assessment techniques to clarify previous, conflicting reports. Twelve healthy volunteers (6 men, 6 women) performed six classic leg cuff tests, three breathing normoxic (Fi(O2) = 0.21) and three breathing hypoxic (Fi(O2) = 0.12) gas, using a single blinded, Latin squares design with 5-min washout between trials. Continuous measurements of middle cerebral artery blood flow velocity (CBFv; DWL MultiDop X2) and radial artery blood pressure (ABP; Colin 7000) were recorded in the supine position during a single experimental session. Autoregulation index (ARI) scores were calculated using the model of Tiecks et al. (Tiecks FP, Lam AM, Aaslid R, Newell DW. Stroke 26: 1014-1019, 1995) from ABP and CBFv changes following rapid cuff deflation (cuff ARI) and from ABP to CBFv transfer function, impulse, and step responses (TFA ARI) obtained during a 4-min period prior to cuff inflation. A new measure of %CBFv recovery 4 s after peak impulse was also derived from TFA. AH reduced cuff ARI (5.65 +/- 0.70 to 5.01 +/- 0.96, P = 0.04), TFA ARI (4.37 +/- 0.76 to 3.73 +/- 0.71, P = 0.04), and %Recovery (62.2 +/- 10.9% to 50.8 +/- 9.9%, P = 0.03). Slight differences between TFA and cuff ARI values may be attributed to heightened sympathetic activity during cuff tests as well as differential sensitivity to low- and high-frequency components of CA. Together, results provide consistent evidence that CA is impaired with AH. In addition, these findings demonstrate the potential utility of TFA ARI and %Recovery scores for future CA investigations.
authors: Dept. of Biology, Univ. of Colorado at Colorado Springs, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80918, USA. asubudhi@uccs.edu
authors: Andrew W
authors: AW
authors: Subudhi
authors: Ronney B
authors: RB
authors: Panerai
authors: Robert C
authors: RC
authors: Roach
mesh_terms: D000208:Acute Disease; D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation; D005260:Female; D005583:Fourier Analysis; D006339:Heart Rate; D006706:Homeostasis; D006801:Humans; D000860:Hypoxia / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D008365:Manometry; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008955:Models, Cardiovascular; D010100:Oxygen / Q000097:blood; D011237:Predictive Value of Tests; D017534:Radial Artery / Q000503:physiopathology*; D020127:Recovery of Function; D012720:Severity of Illness Index; D016037:Single-Blind Method; D013997:Time Factors; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen