Parallel recovery of consciousness and sleep in acute traumatic brain injury

Abstract

Objective: To investigate whether the progressive recuperation of consciousness was associated with the reconsolidation of sleep and wake states in hospitalized patients with acute traumatic brain injury (TBI).

Methods: This study comprised 30 hospitalized patients (age 29.1 ± 13.5 years) in the acute phase of moderate or severe TBI. Testing started 21.0 ± 13.7 days postinjury. Consciousness level and cognitive functioning were assessed daily with the Rancho Los Amigos scale of cognitive functioning (RLA). Sleep and wake cycle characteristics were estimated with continuous wrist actigraphy. Mixed model analyses were performed on 233 days with the RLA (fixed effect) and sleep-wake variables (random effects). Linear contrast analyses were performed in order to verify if consolidation of the sleep and wake states improved linearly with increasing RLA score.

Results: Associations were found between scores on the consciousness/cognitive functioning scale and measures of sleep-wake cycle consolidation (p < 0.001), nighttime sleep duration (p = 0.018), and nighttime fragmentation index (p < 0.001). These associations showed strong linear relationships (p < 0.01 for all), revealing that consciousness and cognition improved in parallel with sleep-wake quality. Consolidated 24-hour sleep-wake cycle occurred when patients were able to give context-appropriate, goal-directed responses.

Conclusions: Our results showed that when the brain has not sufficiently recovered a certain level of consciousness, it is also unable to generate a 24-hour sleep-wake cycle and consolidated nighttime sleep. This study contributes to elucidating the pathophysiology of severe sleep-wake cycle alterations in the acute phase of moderate to severe TBI.

Figure 1. Association between cognitive and consciousness recovery and the sleep-wake cycle

(A) Parallel evolution of the Rancho Los Amigos scale of cognitive functioning (RLA) score and daytime activity ratio in the 30 patients assessed over 233 days. Black dots indicate the mean daytime activity ratio per score on the RLA scale, generated within the mixed model equation, and black bars represent SEM. The linear contrast analysis was statistically significant (p < 0.001). (B) Parallel evolution of the RLA score and nighttime sleep duration. Black dots indicate the mean nighttime sleep duration (minutes) per score on the RLA scale, generated within the mixed model equation, and black bars represent SEM. The linear contrast analysis was statistically significant (p = 0.002). (C) Parallel evolution of RLA score and nighttime fragmentation index. Black dots indicate the mean nighttime fragmentation index per score on the RLA scale, generated within the mixed model equation, and black bars represent SEM. The linear contrast analysis was statistically significant (p < 0.001).

Figure 2. Examples of actigraphic findings in relation to Rancho Los Amigos scale of cognitive functioning (RLA) scores

Examples of typical actigraphic findings for RLA ranging from 3 to 5 (left panel), and RLA ranging from 6 to 8 (right panel). Total activity counts for each minute of recording are illustrated by vertical dark lines, on a scale of 0 to 1,000 activity counts. Daytime hours (07:00–22:00 hours) are shown in yellow and nighttime hours (22:00–07:00 hours) in blue. Daily daytime activity ratios (DAR) are indicated at the bottom of each actogram.