Page:Risk of performance errors due to sleep loss, circadian desynchronization, fatigue, and work overload.pdf/19

 demonstrates the occurrence of sleep loss, fatigue, and circadian desynchronization on orbit. One could therefore conclude that, based on the ground evidence, astronauts do indeed face a realistic risk of performance errors.

It is essential, however, to accurately characterize the performance effects arising from sleep loss, fatigue, circadian desynchronization, and work overload more fully in the space flight environment so that individualized countermeasures can be implemented to prevent or reduce the risk. BHP research activities aim to determine the best measures and tools to assess cognitive performance in space and to characterize the effects of sleep loss, fatigue, extended work shifts, circadian desynchronization, and work overload on cognitive performance in this environment.

As detailed above, astronauts and ground personnel are exposed to many factors that may force their schedules away from the normal 24-hour routine: shift work, extended work hours, timeline changes, slam shifting, prolonged light of a lunar day, a Mars sol on Earth, a Mars sol on Mars, and abnormal environmental cues (e.g., inadequate or inappropriate light exposure). In addition, their quantity of sleep, particularly during critical mission operations, tends to be reduced due to a variety of operational, environmental, and individual factors. Extensive ground-based evidence demonstrates that reduced sleep increases the risk of performance errors, injuries, and accidents. As a result, a validated biomathematical model that instantiates the biological dynamics of sleep need and circadian timing could predict astronaut performance relative to fatigue and circadian desynchronization (Dinges, 2004). Such models could also provide a means by which to optimally schedule targeted countermeasures for maintaining astronaut performance. Various biomathematical models that seek to achieve these goals are under development (Mallis et al., 2004; Dean et al., 2007; Kronauer et al., 2007).

Two biomathematical models are discussed here: the Astronaut Scheduling Assistant, and the Circadian, Neurobehavioral Performance, and Subjective Alertness Model. Both of these models are based on extensive evidence that shows that the temporal dynamics and level of cognitive performance during wakefulness are the result of the interaction of sleep homeostatic drive and circadian timing (e.g., Borbély and Achermann, 1999). Both models incorporate predictions that are based on countermeasures. These predictions allow for the evaluation of the risk and safety of sleep/wake and work schedules during both the planning and the execution of space missions. Prospective studies on the accuracy of these model predictions remain to be done on Earth in conditions that simulate many of the sleep loss and circadian provocations that occur in space flight. Such studies are essential and may indicate the need for additional model parameters and changes in model structure.

The Astronaut Scheduling Assistant software tool, which was developed in 2007 by David Dinges and Hans Van Dongen, is based on a validated biomathematical model that relates cognitive performance to the neurobiology of sleep and wakefulness and to the biological clock. As previously discussed, studies in recent years have documented that the detrimental effects on cognitive performance of chronic sleep loss accumulate linearly across consecutive days of sleep restriction below 7 hours per day (Belenky et al., 2003; Van Dongen et al., 2003; Molicone et al., 2007; Mollicone et al., 2008). This model therefore takes into account cumulative sleep loss and more accurately predicts performance than traditional models (Avinash et al., 2005). For more information, refer to Appendix 2 of this report. Differential vulnerability to the effects of sleep loss (Van Dongen et al., 2004) and night work (Czeisler et al., 2005) on performance must also be addressed by biomathematical models of astronaut performance because