Chapter 2 Reproducibility analysis As can be seen in the tables S3 and S4 (supplemental material), all ICC’s have wide overlapping confidence intervals. The confidence interval width can only be decreased by inclusion of many more (>100) subjects. Only then significance of the apparent differences between ICC values may be deduced. Now, only the parameters with ICC values above 0.9 can be considered reproducible at an acceptable level. During spontaneous breathing, this only holds for CBFV in the morning and afternoon (0.93), BP in the morning (0.91) and RAP (0.91) in the afternoon. In paced breathing this only holds for CBFV (0.94) and RAP (0.92) in the afternoon. None of the autoregulation parameters shows adequate repro- ducibility. Discussion Our evaluation of four different signal-processing strategies shows that there is only limited influence on dCA parameters. Spectral smoothing 18 compared to epoch averaging 32 was suggested to improve detection of very low frequency cerebral haemodynamic oscillations. Our results only show slight improvement of coherence using spectral smoothing without an effect on gain and phase. Also the smoothness priors detrending method 29 results in higher coherence in the very low frequency range with hardly any effect on gain and phase. It seems therefore that the gain and phase parameters in the frequency range from 0.04- 0.16 Hz are very robust for the different signal processing methods applied. Impaired early morning (6-8am) cerebral autoregulation was shown compared to evening (6-8pm) measurements in 20 healthy subjects 3. To assess ARI the investigators used the thigh cuff inflation-deflation method. We investigated our 19 subjects in the morning (10 am) and afternoon (2 pm) and could not demon- strate significant differences in dCA parameters using transfer function analysis. The ARI values extracted from the transfer function neither showed morning versus afternoon differences. Based on our results, no preference can be made for morning or afternoon dCA measurements. However, we can not rule out the possible influence on dCA due to circadian rhythms. Neither can we counter the morning-evening differences shown by Ainslie et al, since our morning and afternoon measurements were at different times (10 am and 2 pm). 32
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