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Chapter 7 studied dCA in AD patients. They found, compared to healthy elderly increased gain in the low frequency band (0.07-0.2 Hz) while using squat- stand maneuvers to evoke ABP variation. These maneuvers might, because of larger ABP variation, challenge dCA more and therefore make dCA evaluation more sensitive to differences in cerebral blood flow control. Limitations Our studies maybe have insufficiently addressed the influence of CO2 on dynamic cerebral autoregulation. Both in the studies in healthy volunteers described in chapter 2 and in the study in patients and healthy elderly in chapter 4 etCO2 measurements have been performed. In chapter 2 etCO2 have been recorded in nine of 19 subjects both during spontaneous and paced breathing. Especially during paced breathing, where subjects are likely to increase their tidal volumes and expire more CO2, influence of etCO2 could be seen; etCO2 dropped after the start of paced breathing resulting in lower CBFV. The interaction of this etCO2 change in relation to measures of dCA should be further investigated. From the study in chapter 6 we know that with lower paCO2 both dCA gain and phase are increased. Therefore, paCO2 always needs to be monitored when investigating dCA. Future directions From the results in this thesis and the progressing research in the field of dynamic cerebral autoregulation new directions in dCA analysis need to evolve towards multivariate analysis. The complex interaction between arterial blood pressure, paCO2 and metabolic stimuli such as visual stimulation needs to be disentangled by developing new experimental setups that try to control the strength of each individual stimulus and analyze the resulting CBFV in relation to each of the stimuli. Unless ABP is constant, the continuous process of dCA is interfering with any other cerebral hemodynamic process studied, e.g. neurovascular coupling. When quantifying NVC, CBFV variation is partly caused by the response to e.g. visual stimuli and partly by the dCA response to ABP variation. In chapter 5 we showed estimated NVC parameters are more reliable when also taking into account the effects of dCA on CBFV. When studying dCA, other processes influencing blood pressure and/or cerebral blood flow might need to be studied. A process that might need to be investigated in conjunction with dCA quantification is the baroreceptor response. Baroreceptors sense in- and decreases of blood pressure in the aorta and carotid arteries and send a 130


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