Cerebral blood flow response to cardiorespiratory oscillations in healthy humans

Dynamic cerebral autoregulation is preserved during orthostasis and intrathoracic pressure regulation in healthy subjects: A pilot study

“…In another study in which advanced nonlinear methods for evaluating coupling strength in cerebrovascular regulation were used, increased coupling strength between MAP and MCA blood velocity was also found in healthy subjects during passive tilt (Porta, Bari, et al, 2023), although this finding was probably not a sign of impaired dynamic CA (Gelpi et al, 2022). In line with these reports, we have previously shown an enhancement of ABP variability accompanied by an increase in the wavelet phase coherence between ABP and ICA blood velocity at Mayer wave frequency (around 0.1 Hz) during hypovolemia and exercise-induced sympathetic activation in healthy subjects; however, the low values of the wavelet phase coherence and the SI over the LF interval indicated intact dynamic CA (Holme et al, 2023;Skytioti et al, 2018a). On the other hand, sympathetic nervous activity does not seem to be altered by −7 cm H 2 O of intrathoracic pressure due to impedance breathing (Winklewski et al, 2019).…”

“…The efficiency of CA to buffer changes in ABP and maintain stable cerebral perfusion is influenced by several physiological mechanisms such as PaCO 2 , body temperature, the autonomic activity, neuronal activation, intracranial and intrathoracic pressure, and blood rheology (Claassen et al., 2021 ; Holme et al., 2023 ; Panerai, 2014 ; Panerai et al., 2010 ; Zhang et al., 2002 ). During our experiments, the median SI for the variable pairs ABP‐ICA blood velocity, ABP‐right MCA velocity, and ABP‐left MCA velocity was low (<0.2), indicating strong phase difference variability, nonstationarity (Latka et al., 2005 ; Panerai, 2014 ), and thus efficient CA in the VLF range.…”

“…Wavelet phase coherence, a linear operation, that quantifies the linear relationship between wavelet‐transformed data. An appendix on the wavelet method can be found in a recent article from our group (Holme et al., 2023 ). A low value of wavelet phase coherence indicates that there is no particular phase relationship between the two oscillating variables at a specific frequency.…”

“…The sympathetic nervous system is considered to be an important regulator of CA (Holme et al, 2023;Mitsis et al, 2009;Panerai, 2014) while a differential control of the sympathetic nervous activity in the systemic and the cerebral circulation (Ainslie et al, 2009;Cassaglia et al, 2008aCassaglia et al, , 2008b) has been suggested. An orthostatic stress that reduces CO and increases sympathetic activity has been shown to result in sympathetic cerebral vasoconstriction (Levine et al, 1994), and enhance the efficiency of CA (Holme et al, 2023). The mild orthostatic challenge in our experiments has probably resulted in sympathetic activation, following the mild drop in CO, due to the baroreflex (Charkoudian et al, 2005), and might have contributed to the observed drop in ICA blood flow and the fluctuations in CA efficiency.…”

“…The sympathetic nervous system is considered to be an important regulator of CA (Holme et al, 2023;Mitsis et al, 2009;Panerai, 2014) while a differential control of the sympathetic nervous activity in the systemic and the cerebral circulation (Ainslie et al, 2009;Cassaglia et al, 2008aCassaglia et al, , 2008b) has been suggested. An orthostatic stress that reduces CO and increases sympathetic activity has been shown to result in sympathetic cerebral vasoconstriction (Levine et al, 1994), and enhance the efficiency of CA (Holme et al, 2023).…”