The current study investigated heart rate (HR) and heart rate variability (HRV) across day and night in patients with disorders of consciousness (DOC). the authors recorded 24-h ECG in 26 patients with unresponsive wakefulness syndrome (UWS) and (exit) minimally conscious state ((e)MCS).
A persistent vegetative state or post-coma unresponsiveness is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. After four weeks in a vegetative state, the patient is classified as in a persistent vegetative state.
A minimally conscious state is a disorder of consciousness distinct from persistent vegetative state and locked-in syndrome. Unlike persistent vegetative state, patients with minimally conscious state have partial preservation of conscious awareness.
To examine diurnal variations, HR and HRV indices in the time, frequency, and entropy domains were computed for periods of clear day and nighttime.
Results indicate that patients interbeat intervals (IBIs) were larger during the night than during the day indicating heart rate slowing. Additionally, higher heart rate variability entropy was associated with higher EEG entropy during the night. Patients in unresponsive wakefulness syndrome showed larger interbeat intervals compared to patients in minimally conscious state, and patients with non-traumatic brain injury showed lower ECG entropy than patients with traumatic brain injury.
Thus, cardiac activity varies with a diurnal pattern in patients with disorder of consciousness and can differentiate between patients diagnoses and etiologies. Moreover, also the interaction of heart and brain appears to follow a diurnal rhythm.
Thus, heart rate and heart rate variability seem to mirror the integrity of brain functioning and consequently might serve as supplementary measures for improving the validity of assessments in patients with disorder of consciousness.