Phase-Dependent Reversal of Respiratory–Cortical θ Precedence Across Anesthetic Loss and Recovery of Consciousness

Background: The temporal relationship between respiratory dynamics and cortical oscillatory changes during transitions of consciousness remains poorly characterized. While both respiratory function and EEG θ-band power undergo abrupt changes during anesthetic induction and emergence, the causal directionality of their coupling has not been systematically examined. Methods: From an initial pool of approximately 5,800 VitalDB v1.0.1 cases, 169 passed quality control with valid induction, emergence, and respiratory data; all 169 had identifiable θ-power transitions. θ-Power transition dynamics were analyzed in the 163-case subset meeting strict transition-significance criteria, and temporal precedence plus heart rate variability (HRV) in all 169. θ-Band (4–8 Hz) instantaneous power was computed from 128 Hz frontal EEG, smoothed with a 60 s window, and subjected to PELT change-point detection to identify sharp θ-power transitions. Three respiratory channels (VENT_RR, ETCO2, RR_CO2) were analyzed for concurrent change-points within ±600 s of each θ transition. Temporal precedence (±60 s tolerance) classified each case as respiratory-first, simultaneous, or θ-first. HRV (SDNN) was compared before and after θ transitions. Sensitivity to the tolerance window was assessed across 30–120 s. Results: θ-Power transitions were detected in 100% of cases for both induction and emergence. A striking asymmetric causality pattern emerged: during induction, θ-power transitions preceded respiratory changes (ETCO2: θ-first : resp-first = 19 : 1; R = 0.05); during emergence, respiratory recovery preceded θ-power restoration (ETCO2: resp-first : θ-first = 14 : 3; R = 4.67). This asymmetry was consistent across ETCO2 and RR_CO2 channels and remained robust across all tested tolerance windows (30–120 s). HRV increased after induction transitions (median ratio 1.18) and decreased after emergence transitions (median ratio 0.90). No significant differences were found between sevoflurane and propofol subgroups (p = 0.687). Conclusions: The coupling between respiratory dynamics and cortical θ-power during consciousness transitions is bidirectional but phase-dependent. During induction (loss of consciousness), cortical deactivation precedes respiratory depression; during emergence (recovery of consciousness), respiratory restoration precedes cortical reactivation. This asymmetric temporal pattern may reflect fundamentally different timescales governing cortical and autonomic recovery pathways, with bottom-up vagal priming facilitating cortical reactivation during emergence.