Estimating Day-to-Day Circadian Rhythm in Patients with Severe Acquired Brain Injury at the Beginning of In-Hospital Rehabilitation

Background: Patients with severe acquired brain injury (sABI) are likely to have a disturbed circadian rhythm in the early phase of neurorehabilitation. Circadian rhythm and sleep play an important role in the rehabilitation of patients with severe acquired brain injury (sABI). Research has also pointed out the importance of investigating novel ways of assessing sleep and circadian rhythm in patients with acquired brain injury. Established methods fail to apply to the heterogeneous and fluctuant biological or behavioral signals of the patients with sABI. Accelerometry (ACC) has proven a useful measure of circadian rhythm in sABI patients. However, ACC is unavailing if patients have limited motor activity due to a low consciousness level or severe paresis. Heart rate (HR) could be a viable alternative. In this study, we aim to present a novel model for the estimation of circadian rhythm and rhythm characteristics in both motor-active and -inactive patients using ACC and HR. Furthermore, we aim to present the results of the model in patients with sABI during their first three weeks of subacute in-hospital neurorehabilitation. Methods: An explorative observational study. Continuous recordings of ACC and electrocardiography were conducted. The suggested model was applied to examine circadian rhythms. Results: This study has proven the feasibility of a novel model for the analysis of circadian rhythm. Twenty-nine patients were included, 20 motor active and nine motor inactive. Estimates of rhythm characteristics have been presented along with estimates of circadian rhythm presence or absence for both groups. Conclusions: The model has been successfully applied in a population of patients with sABI. The circadian rhythm of patients undergoing in-hospital neurorehabilitation is fluctuating across time and highly variant between subjects within the first three weeks after admission to sub-acute neurorehabilitation.