Published Online
on February 26, 2004

A more recent version of this article appeared on April 1, 2004

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Submitted on December 18, 2003
Accepted on December 22, 2003

Dynamic Autoregulation Testing in the Posterior Cerebral Artery

C. Haubrich MD^*; A. Wendt Cand.Med.; R. R. Diehl PhD; and C. Klötzsch MD

From the Department of Neurology, University Hospital Aachen, Aachen (C.H., A.W.); Department of Neurology, Alfred-Krupp Krankenhaus Essen, Essen (R.R.D.); and Kliniken Schmieder, Allensbach und Hegau-Klinikum Singen, Singen (C.K.), Germany.

^* To whom correspondence should be addressed. E-mail: Christina.Haubrich{at}t-online.de.

Background and Purpose--Dynamic autoregulation has been studied predominantly in the middle cerebral artery (MCA). Because certain clinical conditions, ie, presyncopal symptoms or hypertensive encephalopathy, suggest a higher vulnerability of autoregulation within posterior parts of the brain, we investigated whether the cerebral blood flow velocity (CBFV) is modulated differently within the posterior cerebral artery (PCA).

Methods--Spontaneous oscillations of CBFV and arterial blood pressure (ABP) in the frequency range of 0.5 to 20 cycles per minute were studied in 30 volunteers (supine and tilted positions). Analysis was based on the "high-pass filter model," which predicts a specific frequency-dependent phase and amplitude relationship between oscillations in CBFV to ABP. These parameters, characterized as phase shift angles and transfer function gains, were calculated from simultaneously recorded beat-to-beat blood pressure and transcranial Doppler signals of the PCA and MCA by means of cross-spectrum analysis.

Results--In the MCA and PCA, phase shift angles were decreased, and gains were elevated with increasing oscillation frequency. The PCA gain values in supine and tilted positions were significantly higher than in the MCA.

Conclusions--The phase and amplitude relationship between CBFV and ABP showed a frequency dependence in the PCA similar to that in the MCA. The study therefore suggests that the high-pass filter model of dynamic cerebral autoregulation can be applied to the PCA. In this model the generally higher gain values in the PCA indicate a lower damping of ABP oscillations, which are transmitted to the posterior part of cerebral circulation.

Key words: spectrum analysis • autoregulation • middle cerebral artery • posterior cerebral artery • ultrasonography, Doppler, transcranial

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