Spectral analysis of cerebrovascular regulation in patients with autonomic dysfunction

Background. Regulation of cerebral blood flow during orthostatic stress has been a major research topic in patients with orthostatic intolerance such as autonomic dysfunction. Spontaneous fluctuations of middle cerebral artery blood flow velocity (MCAFV) recorded with transcranial Doppler (TCD) have been found to contain information related to cerebrovascular regulation, which can be deciphered with spectral analysis. The purpose of this study was to evaluate the differences in cerebrovascular regulation between healthy volunteers and patients with autonomic dysfunction and orthostatic dizziness for using spectral analysis of MCAFV information derived from TCD during supine rest and orthostasis. Methods. Thirteen patients with autonomic dysfunction and orthostatic dizziness were found to have impaired cerebral autoregulation because of failure to maintain adequate cerebral blood flow velocity during a 30-minute head-up tilt study with concomitant TCD and cuff sphygomanometer monitoring. The data of bilateral MCAFV were compared between these 13 patients and 9 healthy volunteers using spectral analysis. Results. Spectral analysis of the MCAFV showed significantly decreased low frequency (LF) power in supine position in the patient group (p = 0.0002). In addition, the spectral power in the very low and low frequency (VLF & LF) ranges remained significantly lower in the patient group after tilting up (p < 0.05). Conclusions. (1). Our study results further support the previous findings that the LF component of the spontaneous fluctuations of MCAFV is important for cerebrovascular regulation. (2) The decreased LF MCAFV power may be a useful indicator or marker of impaired cerebrovascular regulation in patients with autonomic dysfunction.