Rest-Activity Circadian Rhythm and Light Exposure Using Wrist Actigraphy in ICU Patients

Actigraphy (ACTG) is easy to use and has proved reliable in non-critical populations of patients. It has been used to track circadian rest-activity cycles and to identify states of wakefulness and sleep [1]. A more recent study has found that ACTG have a moderate level of agreement with PSG in distinguishing between sleep and wakeful states which is more profound in non-ventilated patients [2]. Moreover, ACTG provides an objective physiological assessment via non-invasive use of motion accelerometers to detect multiplanar gross motor activity [2], indicating purposeful or nonpurposeful movement of patients. Especially, non parametric values (IS: intradaily stability; IV: interdaily variability; L5: least active 5-hour period; M10: most active 10-hour period; and RA: relative amplitude) can quantify circadian rest- activity rhythm providing an indication of circadian rhythmicity. The non-parametric approaches measured in order to investigate 24 hour rest-activity circadian patterns are: M-10 which is the average activity level (counts) of the 10 most active hours indicating patients’ daily activity. Moreover, L-5 is the average activity level (counts) of the least active 5-h period, reflecting patients’ nocturnal activity [3]. The relative amplitude (RA) of the rhythm, is the difference between M-10 and L-5 in the average 24-h pattern, normalized by their sum, ranging between >0 and <14. Higher RAs indicate a more robust 24 hour rest-activity rhythm, reflecting both relatively lower activity during the night and higher activity when awake [2]. Finally, IS provides an estimate of how closely the 24 hour rest-activity rhythm follows the 24 hour light-dark cycle (range: >0 and <1). Higher IS indicates good synchronization to light and other environmental cues that regulate circadian rhythms [3,4,5]. Furthermore, ICU lighting is not typically controlled to cycle with bright light levels during the daytime and darkness at night, as the focus is on medical and nursing care and interventions. Research findings suggest that cycled lighting have positive effects on patient length of stay in the ICU recovery and well-being [6].