Reproducibility of dynamic cerebral autoregulation the recordings the Physiocal procedure, an intermittently occurring calibration routine, was switched off. To measure cerebral blood flow velocity (CBFV) simultaneously in the right and left middle cerebral artery a Transcranial Dop- plersonography device (DWL Multi-Dop® X4, Sipplingen, Germany) was used. The two 2 MHz-probes were held in position by a special head frame. Data analysis ECG, ABP and right and left CBFV signals were recorded on a DAT-tape (TEAC- recorder) and thereafter offline digitised and stored on a PC with an in-house made acquisition and analysis software package (AFOnew version 2.33, IDEE Maastricht®, the Netherlands). The sampling frequency for each signal was set to 250 Hz. An automatic algorithm detected the ECG R-waves and determined the subsequent diastolic, mean and systolic blood pressure and corresponding end- diastolic, mean and peak-systolic CBFV. Artefacts were removed manually by linear interpolation. The beat-to-beat values of ABP and CBFV were resampled with 5 Hz using spline-interpolation 22. From the ABP the overall mean value was subtracted and the CBFVs were normalised with respect to the mean. This resulted in zero-mean signals suited for spectral analysis to estimate the transfer function. The transfer function was calculated by S ( f ) H ( f ) ? xy (1) S xx ( f ) whereSxx(f) is the autospectrum of changes in arterial blood pressure andSxy(f) is the cross-spectrum between the ABP- and CBFV-signals. The transfer function magnitude|H(f)| and phase spectrum (f) were derived from the real partHR(f) and imaginary partHI(f) of the complex transfer function as | H ( f ) |? H R ( f )_ 2 - H I ( f )_2 (2) H ( f ) H( f ) ? arctan I (3) H R ( f ) The squared coherence function 2(f) was estimated by | S ( f ) |2 i 2 ( f ) ? xy (4) S xx ( f )S yy ( f ) whereSyy(f) is the autospectrum of changes in cerebral blood flow velocity. The squared coherence reflects the strength of the linear relationship between ABP and CBFV for each frequency on a scale from 0 to 1. 23
proefschrift gommer inhoud met kaft.indd
To see the actual publication please follow the link above