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Validation of Model Predictions of Alertness, Performance and Sleepiness

Principal Investigator:
Erin E. Flynn-Evans, Ph.D., M.P.H.

NASA Ames Research Center

Biomathematical models hold promise as technological tools that can be used in concert with other tools and strategies to manage fatigue risks in operational settings. A number of biomathematical models have been developed to predict performance impairment stemming from acute and chronic sleep loss, circadian desynchronization, and sleep inertia.

Dr. Erin Flynn-Evans and colleagues will evaluate four candidate models that deserve consideration for future transition to spaceflight operations. The models include the Harvard Circadian Performance Simulation Software, another developed by McCauley and Washington State University, the unified model from BHSAI, and the commercially-available SAFTE FAST model. While the models are based on similar physiological principles, each offers unique attributes that may lend itself to spaceflight application.

Technical Summary

Dr. Flynn-Evans’ project team will conduct a rigorous comparison of the model predictions of alertness. The model algorithms are based on measures obtained in laboratory and field studies. The standard objective measure of performance is the psychomotor vigilance task (PVT), a short reaction-time test that is highly sensitive to sleep loss and circadian disruption. Circadian phase has been measured by 6-sulfatoxymelatonin (aMT6s) acrophase and temperature nadir. The result from the comparisons will then be used to gain a better understanding of the capabilities and limitations of each model and to provide guidance on confidence limits for the model predictions.

Five data sets from the laboratory and field that encompass a wide range of imposed sleep schedules will be used for the comparative analysis of the models. The available data sets includes those from short-haul commercial aviation pilots, ground support personnel for a Mars mission working a non-24 hour schedule, International Space Station (ISS) flight controllers working overnight shifts, a simulated “slam shift” (participants were required to repeatedly invert their sleep/wake schedule) with blue light and caffeine administration, and a lab study assessing the effectiveness of a melatonin countermeasure.

The aim of the comparative analysis will focus on determining how well the proposed models estimate sleep-deprivation and circadian outcomes traditionally assessed by the clinical gold- standard of performance, the PVT. The PVT provides several outcome metrics, though two of the performance indicators are most commonly focused upon number of lapses, or responses > 500 ms, and the inverse mean reaction time (1/RT), also referred to as response speed.

Analytical techniques may include Bland & Altman, non-linear mixed models and visualization methods to better assess the time-related effects of predicted and actual circadian phase. The analysis will compare predicted outcomes from the models with the measures collected from the study data sets for performance and circadian phase.

Earth Applications

Technological devices such as models are envisioned as potentially powerful tools for fatigue management in challenging work environments such as transportation. Models are already in use in some settings such as commercial aviation as a means of evaluating flight crew schedules for potential fatigue-related risks. This is despite the fact that most models have not been rigorously evaluated and validated for the operations to which they are being applied and that many users are not fully aware of the limitations in which the results should be interpreted and applied.

This evaluation of these models will provide NSBRI and NASA and the larger community of researchers and safety management personnel with a comprehensive understanding of the capabilities and limitations of each model. NASA operational personnel will also be briefed prior to deployment of any of the models.