No abstract

Cognitive efforts induce lateralized hemodynamic changes in the cerebral hemispheres, which can be demonstrated by blood flow velocity (BFV) measurements using transcranial Doppler sonography (TCD) (Droste et al. 1989;Hartje et al. 1994;Schmidt et al. 1999;Deppe et al. 2004). The validity of Doppler data has been proven by functional magnetic resonance imaging (fMRI) studies (Schmidt et al. 1999;Weiss et al. 2003). Beside localized increase of cerebral blood flow, cognitive effort also induces considerable autonomic changes, including the elevation of arterial blood pressure (ABP), heart rate (HR) and respiratory rate (Rr) (Oldfield 1971;Moody et al. 2005; Yoshino and Matsouka 2005). These systemic factors also influence cerebral circulation, and their effects should always be considered when interpreting both functional TCD and functional MRI results (Stroobant and Vingerhoets 2000). However, due to technical difficulties, the parallel measurement of cerebral blood flow and cardiac-as well as respiratory autonomic parameters has been performed only in few cases (Wang et al. 2005). In our previous study (Szirmai et al. 2005), in which we described the correlation between blood flow velocity and central frequency of EEG, we found that during cognitive tests, after a transitory increase, blood flow velocity returned almost to the initial level, despite increasing blood pressure and heart rate. These observations suggested analogy with the physiological effect of hyperventilation induced vasoconstriction (Malatino et al. 1992), because temporary decrease of flow velocity could not be explained by the metabolic-and/or neurogenic theory of cerebral blood flow regulation. We presumed that the unexpected decrease of blood flow velocity was due to hypocapnia evoked by hyperventilation, and that this systemic effect interfered with the local cerebral circulatory changes induced by cognitive processes. Similar results were found by fMRI investigations performed during controlled hyperventilation (Posse et al. 1997).In the present study, we investigated the interactions between cognition-induced changes in cerebral circulation and changes in autonomic functions by simultaneously recording blood flow velocity in the middle cerebral arteries (MCA) and cardiac as well as respiratory parameters during mental arithmetic task.