Infra-slow fluctuations in heart and brain

The human brain pacemaker: Synchronized infra-slow neurovascular coupling in patients undergoing non-pulsatile cardiopulmonary bypass

In non-pulsatile cardiopulmonary bypass surgery, middle cerebral artery blood flow velocity (BFV) is characterized
by infra-slow oscillations of approximately 0.06 Hz, which are paralleled by changes in total EEG
power variability (EEG-PV), measured in 2 s intervals. Since the origin of these BFV oscillations is not
known, we explored their possible causative relationships with oscillations in EEG-PV at around 0.06 Hz.
We monitored 28 patients undergoing non-pulsatile cardiopulmonary bypass using transcranial Doppler
sonography and scalp electroencephalography at two levels of anesthesia, deep (prevalence of burst
suppression rhythm) and moderate (prevalence of theta rhythm).
Under deep anesthesia, the EEG bursts suppression pattern was highly correlative with BFV oscillations.
Hence, a detailed quantitative picture of the coupling between electrical brain activity and BFV was derived,
both in deep and moderate anesthesia, via linear and non linear processing of EEG-PV and BFV signals,
resorting to widely used measures of signal coupling such as frequency of oscillations, coherence, Granger
causality and cross-approximate entropy. Results strongly suggest the existence of coupling between
EEG-PV and BFV. In moderate anesthesia EEG-PV mean dominant frequency is similar to frequency of BFV
oscillations (0.065±0.010 Hz vs 0.045±0.019 Hz); coherence between the two signals was significant in
about 55% of subjects, and the Granger causality suggested an EEG-PV†'BFV causal effect direction. The strength
of the coupling increased with deepening anesthesia, as EEG-PV oscillations mean dominant frequency virtually
coincided with the BFV peak frequency (0.062±0.017 Hz vs 0.060±0.024 Hz), and coherence became significant
in a larger number (65%) of subjects. Cross-approximate entropy decreased significantly from moderate
to deep anesthesia, indicating a higher level of synchrony between the two signals.
Presence of a subcortical brain pacemaker that drives vascular infra-slow oscillations in the brain is proposed.
These findings allow to suggest an original hypothesis explaining the mechanism underlying infra-slow
neurovascular coupling.