Actigraphy in brain-injured patients - A valid measurement for assessing circadian rhythms?

Objective: Actigraphy has received increasing attention in classifying rest-activity cycles. However, in patients with disorders of consciousness (DOC), actigraphy data may be considerably confounded by external movements. Consequently, this study verified whether circadian rhythmicity is (still) visible in actigraphy data from DOC patients after correcting for these external movements. Methods: Wrist actigraphy was recorded over 7-8 consecutive days in DOC patients (diagnosed with unresponsive wakefulness syndrome [UWS; n=19] and [exit] minimally conscious state [MCS/EMCS; n=11]). Presence and actions of clinical and research staff as well as visitors were indicated using a tablet in the patient9s room. Following removal and interpolation of external movements, non-parametric rank-based tests were computed to identify differences between circadian parameters of uncorrected and corrected actigraphy data. Results: Uncorrected actigraphy data overestimated the interdaily stability and intradaily variability of patients9 activity and underestimated the deviation from a circadian 24h rhythm. That is only 5/30 (17%) patients deviated more than 1h from 24h in the uncorrected data, whereas this was the case for 17/30 (57%) patients in the corrected data. When contrasting diagnoses based on the corrected dataset, stronger circadian rhythms and higher activity levels were observed in MCS/EMCS as compared to UWS patients. Day-to-night differences in activity were evident for both patient groups. Conclusion: Our findings suggest that uncorrected actigraphy data overestimates the circadian rhythmicity of patients9 activity as nursing activities, therapies, and visits by relatives follow a circadian pattern itself. Therefore, we suggest correcting actigraphy data from patients with reduced mobility to arrive at meaningful results.