Spectral Analysis of Blood Pressure and Blood Flow Velocity in the Middle Cerebral Artery Using the Maximum Entropy Method (MEM)

Periodical fluctuation of blood pressure (BP) is known to be the associated with autonomic nerve function. Using transcranial Doppler and the tonometry method, we developed a system for simultaneous measurement of BP and blood flow velocity (FV) in the middle cerebral artery (MCA) for each cardiac beat. We analyzed the relationship between the periodic fluctuations of mean BP (MBP) and mean FV (MFV) . The waves were subjected to spectral analysis using the maximum entropy method (MEM) . The subjects were 12 healthy volunteers, 3 patients with cerebrovascular disease (CVD), and 3 patients with dysautonomia.Spectral analysis of MBP in healthy volunteers indicated two peaks in the power spectrum (LF: under 0.1 Hz and HF: 0.2-0.5Hz) . Similar results were obtained for MFV in healthy volunteers. In some patients with CVD, the fluctuation of MFV tended to be disassociated from that of MBP. LF of MFV was lower than that of MBP. In the patients with dysautonomia, analysis of MBP revealed a significantly lower LF. Analysis of MFV showed variation between normal and lower LF. From these results, we classified the manner of LF into 4 patterns.LF (Mayer wave) is considered to reflect symptomatic nerve function. Disassociation of the fluctuation of MBP form that of MFV suggests, a specific feature of the autonomic nerve system in the brain. This method seems to be useful clinically in assessing autonomic nerve function and cerebral hemodynamics under various loads.