Alterations in respiratory heart rate variability in brain-injured neurointensive care unit patients compared with healthy humans

OBJECTIVE: Respiratory heart rate variability (RespHRV), the variation in heart rate in phase with breathing, is mainly generated by central brainstem mechanisms. Its characteristics in brain-injured patients are poorly understood. The objective of the study was to characterize RespHRV amplitude and phase in brain-injured patients compared to healthy participants. METHODS: We analyzed 55 brain-injured patients and 31 healthy controls. Physiological signals were recorded and processed to extract RespHRV amplitude and phase. Group differences were assessed using Mann-Whitney and Watson-Williams tests. In an additional analysis, 55 patients' RespHRV amplitude and phase were modeled using generalized linear mixed models to evaluate the impact of sedation, ventilation mode, vasoactive and analgesic drugs, and time. RESULTS: Compared to controls, brain-injured patients exhibited a significantly lower RespHRV amplitude (1.04 [0.45, 1.96] vs. 6.21 [4.08, 9.34] bpm; p < 0.001) and an inverted RespHRV phase, with peak heart rate occurring during expiration rather than inspiration. Mixed-effects modeling revealed that machine-triggered ventilation and high level of sedation induced a significant reduction in RespHRV amplitude. CONCLUSIONS: Brain-injured patients demonstrate markedly impaired central generation of RespHRV. SIGNIFICANCE: This profound alteration of RespHRV reflects impaired brainstem control and offers a potential physiological marker of autonomic and neurological recovery.