![]() Therefore, researchers and clinicians are looking for alternative or adjunct measures that (i) do not rely on patients’ behavioral responses, (ii) are time and cost efficient, (iii) and can be easily applied at beside. However, they require special expertise, come with high time and financial requirements and often rely on tasks that are still challenging for patients. Approaches based on neuroimaging methods such as functional magnetic resonance imaging (fMRI) or electroencephalography (EEG) have been used as additional tools to improve the validity of DOC diagnoses. Hence, distinguishing between UWS and (E)MCS continues to be a challenge in clinical practice, and the rate of misdiagnoses is high (i.e., ∼40%). ![]() Consequently, the absence of evidence for consciousness must not be mistaken for evidence of its absence. Finally, the fluctuating levels of consciousness carry the risk of examinations taking place during windows of unconsciousness. ![]() This is because patients may be unable to respond behaviorally (and thus give evidence of their consciousness) for example due to sensory or motor impairments. Unfortunately, behavioral assessments involve the risk of underestimating the level of consciousness. Thus, while patients with UWS are assumed to be unconscious, patients in MCS and EMCS are assumed to be (minimally) conscious.Ĭlinical diagnoses are usually based on observations of the patients’ behavior using for instance the Glasgow Coma Scale for acute situations or the Coma Recovery Scale-Revised (CRS-R) for tracing their development during recovery. If patients can communicate functionally and use objects adequately, their state is denoted as emergence from minimally conscious state (EMCS). More specifically, while patients with an unresponsive wakefulness syndrome (UWS) show some return of arousal (i.e., phases of sleep and wakefulness ) without signs of awareness during behavioral assessment, patients in a minimally conscious state (MCS) show inconsistent but reproducible signs of awareness that can be differentiated from reflexive behavior (e.g., response to commands, visual pursuit, intentional communication). In patients living with DOC, wakefulness is preserved but awareness is only intermittently present or completely absent. In a simplified approach, two major components are thought to be necessary for consciousness: wakefulness (i.e., the level of arousal) and awareness of the environment and the self (i.e., contents of consciousness). These states are subsumed under the term ‘disorders of consciousness’ (DOC). Severe brain injury can cause coma and, upon recovery, changes in consciousness often persist. Thus, HR and HRV seem to mirror the integrity of brain functioning and consequently might serve as supplementary measures for improving the validity of assessments in patients with DOC. Moreover, also the interaction of heart and brain appears to follow a diurnal rhythm. Thus, cardiac activity varies with a diurnal pattern in patients with DOC and can differentiate between patients’ diagnoses and etiologies. Patients in UWS showed larger IBIs compared to patients in (E)MCS, and patients with non-traumatic brain injury showed lower ECG entropy than patients with traumatic brain injury. Additionally, higher HRV entropy was associated with higher EEG entropy during the night. ![]() ![]() Results indicate that patients’ interbeat intervals (IBIs) were larger during the night than during the day indicating HR slowing. To examine diurnal variations, HR and HRV indices in the time, frequency, and entropy domains were computed for periods of clear day- (forenoon: 8am-2pm afternoon: 2pm-8pm) and nighttime (11pm-5am). We recorded 24-h ECG in 26 patients with DOC (i.e., unresponsive wakefulness syndrome and (exit) minimally conscious state ). The current study investigated heart rate (HR) and heart rate variability (HRV) across day and night in patients with disorders of consciousness (DOC). ![]()
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