Chapter 3 CVR the autoregulation curve is lifted and narrowed more, resulting in less effective autoregulation i.e. lowered phase angle. Concerning dCA gain, Panerai et al 25 showed CO2-effects resulted in lowered critical closing pressure in hypercapnic conditions whereas the resistance area product remained nearly unchanged. This might explain the slightly decreased dCA gain we found post versus pre-ACZ testing, since for the same change in ABP the percentage change in CBFV is less. Many authors 9, 15, 26, 30 have stated that CVR and dCA are testing different cerebrovascular control properties. The increase in CBFV provoked by ACZ is commonly assumed to work via carbonic anhydrase inhibition resulting in perivascular acidosis leading to vasodilatation 17, 35, although this is debated by others 12. Conversely, dynamic cerebral autoregulation involves control of CBFV based on changes in cerebral perfusion pressure. However, it is also known that pCO2 levels influence properties of dCA 25. In this study dCA parameters based on transfer function analysis were deter- mined during a CVR-test. Our results illustrate the ambiguity of the relation between CVR and dCA testing, since on the one hand there was a clear-cut effect of CBFV-increase on dCA but on the other hand the correlation of the results of both tests was poor, which supports that at least partly different phenomena are studied. Further research is needed to examine the interaction between both phenomena. Limitations of our study concern both selection of the kind of patients and the dCA method used. Regarding the first, this study was performed in first ever lacunar infarct patients. To investigate the influence of the infarct and the statin treatment a more extensive study in this patient group as well as in healthy subjects is recommended. Regarding the method used to quantify dCA; it is based on transfer function analysis and depends on spontaneous blood pressure variations. This means that no external stimulus is delivered and no additional burden is put on to the pa- tient. Yet, a possible limitation could be insufficient arterial blood pressure variability. The method requires sufficient variability in both blood pressure and cerebral blood flow velocity in the frequency range of interest. This becomes expressed in the coherence between blood pressure and flow, which in our case should exceed 0.1 in the dCA frequency band of interest. The coherence levels in this study did exceed this value. 54
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