SPONTANEOUS BLOOD-PRESSURE OSCILLATIONS AND CEREBRAL AUTOREGULATION

The relationship between spontaneous oscillations in cerebral blood fl ow velocity (CBFV) and arterial blood pressure (ABP) was analysed in n ormal subjects in order to evaluate whether these relationships provid e information about cerebral autoregulation. CBFV was measured using t ranscranial Doppler sonography and continuous ABP and heart rate using Finapres in 50 volunteers. Measurements were made over 5 min in a sup ine position and 6 min in a tilted position. Coefficients of variation were calculated using power-and cross-spectral analysis in order to q uantify amplitudes within two frequency ranges: 3-9 cycles per min (cp m) (M-waves); and 9-20 cpm (R-waves). Correlations, coherence values, phase angle shifts and gains were also computed between corresponding waves in CBFV and in ABP. A clear correlation was seen for M-waves and R-waves between CBFV and ABP and coherence values were large enough t o calculate phase angle shifts and gains. Phase angles for M-waves wer e larger and gains lower than was the case for R-waves, either tilted or supine. These data are consistent with a highpass filter model of c erebral autoregulation. Relatively high CBFV/ABP gain values (between 1.4 and 2.0) suggest that the principle of frequency-dependent vascula r input impedances has to be considered in addition to autoregulatory feedback mechanisms. Spontaneous ABP oscillations in the M-wave and R- wave ranges may serve as a basis for continuous autoregulation monitor ing. (C) 1998 Rapid Science Ltd.