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# proefschrift gommer inhoud met kaft.indd

Chapter 3
From the resulting transfer functions, coherence, phase angle and gain were
calculated in the low frequency (LF) range from 0.04-0.16 Hz where autoregula-
tion is active and in the high frequency (HF) range from 0.2-0.4 Hz which is too
fast for autoregulation to work.
Cerebrovascular reactivity was quantified by equation 5. In the baseline, before
ACZ infusion, the average of CBFV is taken from a visually inspected artefact
free episode (CFBVbase). After ACZ infusion another artefact free episode of
CBFV is averaged to determine CBFVACZ.
CBFV / CBFV
CVR ? ACZ base »100% (5)
CBFVbase
Statistical analysis
The Wilcoxon signed ranks test was used to compare the calculated parameters
from the transfer function before and after ACZ administration. Linear regres-
sion was used to evaluate the relation between CVR and dCA parameters.
Results
It was feasible to determine CVR in all 29 subjects; however, due to a decreased
ultrasound permeability of the transtemporal bone window, dCA evaluation was
not possible in five subjects. They were excluded from this study. In the remain-
ing 24 subjects, data from one recording side (4 left, 1 right MCA) were also
excluded for further analysis because of excessive CBFV measuring artefacts. In
these five subjects parameter values derived from the other, artefact-free, re-
cording side were used. Statistical testing of the remaining 19 left and right side
derived parameters showed no significant side differences. Therefore, parameter
values of the left and right MCA were averaged for each of these 19 individuals.
So, for each of the 24 subjects a complete parameter data set for the evaluation of
CVR and dCA was created.
Median group values and corresponding 95% confidence intervals as computed
for the squared coherence, gain and phase angle before and after ACZ infusion
for the low and high frequency band are given in table 1. Also, the mean heart
rate, mean ABP and mean CBFV with 95% confidence intervals before and after
ACZ infusion as well as the CVR is shown. Note, that the administration of 15
mg/kg ACZ had no effect on mean heart rate and mean ABP.
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