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|Title:||Acute hypoxia impairs dynamic cerebral autoregulation: results from two independent techniques.|
|Citation:||J APPL PHYSIOL, 2009, 107 (4), pp. 1165-1171|
|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.|
|Appears in Collections:||Published Articles, Dept. of Cardiovascular Sciences|
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