Reproducibility of dynamic cerebral autoregulation From the analysis of transfer function dCA parameters it becomes clear that ICC values are very low, meaning that dCA reproducibility is poor. From the dCA parameters ARI has the lowest ICC. Because of the poor ICC’s and the low number of subjects in this study 95% confidence intervals for ICC are very wide and no significant differences can be found between different analysis methods, time-of-day, or breathing strategies. Earlier, Reinhardet al compared spontane- ous versus paced breathing and could not demonstrate significant differences between both methods 26. We do find significant differences for phase and ARI parameter values comparing both breathing methods. ARI is significantly higher in paced compared to spontaneous breathing in all but method I in the afternoon. In order to detect impaired cerebral autoregulation during spontaneous breath- ing dCA phase should, based on our data, be less than 0.4 rad (criterion: mean minus 2 standard deviations). For MMPF the criterion for dCA impairment is a phase value less than 0.2 rad for component 3 and 0.3 for component 4. Due to the large inter- and intrasubject variability, the application of the different meth- ods for the evaluation of dCA, although in good agreement, has limited value for the individual healthy subject. Whether this is also true for diseased populations remains to be investigated. The ICC’s we found for the MMPF method for phase are comparable with the reported values from Huet al 11. Only for paced breathing MMPF has a higher, although not significant, ICC compared to conventional transfer function analy- sis. In contrast with Huet al we found better ICC for ARI, whereas significance in this case cannot be determined. Their low ICC value maybe explained by the fact that Hu et al calculate ARI by applying the Tiecks model only on short data segments, whereas we based the ARI on the estimated transfer function from the recording period of 15 minutes. We also report here ICC values for MMPF gain and the suggested MTFA. For gain MMPF seems to do better than the transfer function analysis, but the MTFA analysis does not seem to be an improvement. 35
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