Key result
Lower signal complexity and HRV are linked to worse 6-month outcomes after moderate-to-severe TBI.
Why the study?
Autonomic nervous system dysfunction and reduced signal complexity occur after TBI, but their relationships with cerebral physiology and functional outcome during neurointensive care remain incompletely understood.
Observational (n=649)
No
Reduced signal complexity and heart rate variability are independently associated with worse functional outcome at 6 months after traumatic brain injury.
Exploratory ANS and complexity metrics post-TBI remain hypothesis-generating; prospective studies needed before any clinical role in NIC.
Background Autonomic nervous system (ANS) dysfunction and reduced signal complexity (SC) appear to occur after traumatic brain injury (TBI) and may reflect impaired physiological adaptability. However, their relationships with cerebral physiology and functional outcome during neurointensive care (NIC) remain incompletely understood. This study explores heart rate variability (HRV), baroreflex sensitivity (BRS) and multiscale entropy-derived SC of systemic and cerebral signals in patients with moderate-to-severe TBI during NIC. Methods This retrospective, single-centre study included 649 TBI patients with intracranial pressure (ICP) monitoring for longer than 24 h, treated in the NIC unit at Uppsala University Hospital, Sweden (2008–2024). HRV, BRS and SC (multiscale entropy complexity index) of heart rate (HR), mean arterial pressure (MAP), ICP, ICP pulse amplitude (AMP) and cerebral perfusion pressure (CPP), respectively, were analysed over the first 10 days of NIC. Associations with demographics, injury severity, NIC physiology (ICP, CPP, pressure reactivity index [PRx]) and 6-month Glasgow Outcome Scale-Extended (GOSE) were assessed using Spearman’s correlations, multivariable ordinal logistic regression and two-variable outcome heatmaps. Results In multivariable regression (adjusted for age, Glasgow Coma Scale motor score [GCS M], pupillary reactivity, ICP, CPP and PRx) higher HRV and SC of each of HR, ICP, AMP and CPP independently correlated with better functional outcome in separate models. Outcome heatmaps demonstrated that reduced SC combined with high ICP, low CPP or high PRx was particularly associated with poor recovery. Lower admission GCS M, barbiturate use and decompressive craniectomy were generally associated with reduced HRV, BRS and SC. Higher ICP and PRx and lower CPP correlated with reduced systemic and cerebral SC. Conclusions Reduced SC and HRV are independently associated with worse outcome after TBI, even when adjusted for conventional NIC predictors. Reduced SC may co-occur with higher ICP and PRx and lower CPP in TBI.
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Alhamdan et al. (2026) conducted an observational in moderate-to-severe traumatic brain injury (n=649). Reduced signal complexity and heart rate variability was evaluated on 6-month Glasgow Outcome Scale-Extended (GOSE). Reduced signal complexity and heart rate variability were independently associated with worse 6-month functional outcome after moderate-to-severe traumatic brain injury.
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