Dynamic cerebral autoregulation in CVR testing Table 1. Median and 95% confidence interval of measured values and calculated dCA parameters before and after ACZ infusion. Before ACZ After ACZ mean heart rate bpm 68 (64-74) 69 (65-73) mean ABP mmHg 102 (96-111) 101 (93-113) mean CBFV cm/s 41 (37-46) 58 (56-70)* Squared coherence LF 0.38 (0.29-0.42) 0.51 (0.39-0.56)* Gain LF %/mmHg 1.3 (1.1-1.4) 1.2 (0.85-1.2)† Phase angle LF rad 1.05 (0.97-1.12) 0.77 (0.58-0.84)* Squared coherence HF 0.44 (0.32-0.50) 0.45 (0.37-0.53) Gain HF %/mmHg 1.7 (1.4-2.1) 1.3 (1.1-1.6)† Phase angle HF rad 0.14 (0.04-0.23) 0.11 (0.02-0.22) CVR % 67 (56-74) * p<0.005,† p<0.05 Wilcoxon signed ranks test Before ACZ infusion, the median phase angle in the low frequency range LF was 1.05 rad indicating normal dCA as compared to reported 28 control values (0.84 ± 0.26 rad). After ACZ infusion (0.77 rad), there was a significant decrease (p<0.005). It is noteworthy, that despite these changes at the end of the test LF values still were within the normal range. After ACZ administration also the squared coherence in the low frequency range was significantly increased as compared to before ACZ infusion, whereas the gain in both the low and high frequency range decreased significantly after ACZ infusion (p<0.05). Figure 1 shows the group averaged phase angle values as a function of frequency before and after ACZ infusion. For frequencies exceeding 0.2 Hz there is no significant difference between the two periods. On the contrary, for the low frequency range a phase angle decrease due to ACZ-infusion can clearly be seen. In our group of 24 patients, median CVR was 67 %. In figure 2 LF before and after ACZ infusion are plotted against CVR for each subject, including linear regression lines and their squared linear correlation coefficients. Although the correlations are rather weak, it appears that after ACZ-infusion LF decreases with increasing CVR value. 49
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