Hypocapnia Induced by Involuntary Hyperventilation during Mental Arithmetic Reduces Cerebral Blood Flow Velocity

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.

The scalability of common paradigms for assessment of cognitive function: A functional transcranial Doppler study

“…The highly significant bilateral CBFV differences observed across time (Tables 1 & 2 ), confirmed that these paradigms could induce NVC responses to cognitive stimulation for all subjects. The two distinct phases of the bilateral CBFV responses to paradigms of different complexity that we observed, are in agreement with the existing literature [ 45 , 46 ]. Different interpretations have been given as to the mechanisms underlying the fast response observed at T2.…”

Decreased connection density and modularity of functional brain networks during n‐back working memory paradigm

“…Finally, alterations in physiological parameters when adapting to increased mental workload could also be considered in a broader context, focusing not only on changes occurring in the brain but on the level of the entire organism. It has been shown that cognitive stimulation may evoke involuntary responses in the cardiorespiratory (Debreczeni et al, 2009;Szirmai et al, 2005) or autonomic nervous systems (Hjemdahl et al, 1989), that may also affect An interesting finding of this study is the presence of two distinct modules-frontal and occipitotemporal-in the control condition that dissociates when cognitive demand increases. This observation is in contrast with the hypothesis that since WM tasks require the involvement of multiple functions such as information encoding and retrieval, short-term memory and increased attention (Roux & Uhlhaas, 2014), an increase in FC during a WM task would be reasonable as being consistent with enhanced cooperation between various brain regions.…”

“…Finally, alterations in physiological parameters when adapting to increased mental workload could also be considered in a broader context, focusing not only on changes occurring in the brain but on the level of the entire organism. It has been shown that cognitive stimulation may evoke involuntary responses in the cardiorespiratory (Debreczeni et al., 2009; Szirmai et al., 2005) or autonomic nervous systems (Hjemdahl et al., 1989), that may also affect indices derived from neural signals. The recently introduced concept of network physiology (Bartsch et al., 2015; Bashan et al., 2012; Ivanov & Bartsch, 2014) provides a framework able to account for such interactions, namely how different organ systems dynamically interact during physiological functioning.…”

Increased prefrontal cortex connectivity during cognitive challenge assessed by fNIRS imaging

“…In our studywhere head movement was minimized -, CBSI proved even more effective in eliminating hemodynamic components with a correlating impact on HbO and HbR signals. However, it has been shown that various means of cognitive stimulation, such as mental arithmetic [52,53] or anagram based tests [46], speech tasks [54]-but in fact, even simple motor tasks such as finger opposition [55]-can elicit not only regional but systemic response as well. These changes in heart rate, mean arterial pressure or partial pressure of CO 2 , by altering cerebral blood flow, can affect HbO and HbR concentrations in an anticorrelating manner albeit with smaller amplitude [14].…”