Performance and Alertness after combined exposure to chronic and acute sleep loss and circadian misalignment

Abstract

Objectives Many individuals are exposed to combinations of acute and chronic sleep loss as well as repeated circadian misalignment in real life. A key question is whether the effects of chronic sleep loss accumulated during the work week can be completely eliminated by long sleep bouts during the weekend. Insight in the recovery process of performance and mood from sleep loss is needed to increase safety in shiftwork and other work environments. Methods and materials Ten healthy volunteers (3 females, mean (SD) age of 28.3 (4.2) years) were studied during a 65- day inpatient stay that included (i) three baseline 24.0-hr days (16-hr wake), (ii) a constant routine protocol (CR1, 41.33-hr wake), (iii) a forced desynchrony (FD) protocol consisting of 12 consecutive 28-hr sleep-wake cycles (18.67-hr wake), (iv) a CR protocol (CR2, 33-52-hr wake) that ended such that the individual´s circadian phase of awakening of the next segment would be the same as during baseline, (v) a 5-day recovery segment with 24-hr days (16-hr wake), and (vi) a CR protocol (CR3; 40.1-40.5-hr wake). Performance was tested every two hours whenever the individual was awake with a 10-min Psychomotor Vigilance Task (PVT), a 2-min Addition test (ADD, number correct) and Visual Analog Scales (VAS) that included Alert-Sleepy scale. The ADD test results were expected to increase across the protocol since there is a learning component. Linear or Generalized linear mixed models were used to compare: (i) Baseline Wake Periods (WP) 2 and 3 vs. last 2 Recovery WP; (ii) CR1 vs CR3; (iii) 1st 6 WP vs 2nd 6 WP of FD; and (iv) 1st 2 vs. last 2 Recovery WP. Additional details of the protocol and original study results are in Gronfier et al 2007 (PNAS). Results PVT median RT and lapses worsened from BL to the end of Recovery, from CR1 to CR3, from 1st to 2nd 6 WP of FD. ADD correct results increased from BL to the end of Recovery, from CR1 to CR3, from 1st to 2nd 6 WP of FD, and from the 1st to last 2nd WP of Recovery. VAS alertness improved from CR1 to CR3. Conclusions The worsening of PVT median and lapses suggests an effect of combined exposure to acute sleep deprivation and circadian misalignment. To what extent this is due to incomplete recovery and/or other elements of the protocol requires further investigation. The stable or improved subjective alertness during these same times is consistent with the known discrepancy between subjective and objective metrics under these condition