Operational Evaluation of a Photic Countermeasure to Improve Alertness, Performance, and Mood During Nightshift Work on a 105-day Simulated Human Exploration Mission to Mars

Overview

The success of human expedition missions critically depend on the ability of the crew to be alert and maintain high levels of cognitive function while operating complex, technical equipment. Optimal human health, performance and safety during space flight requires sufficient sleep and synchrony between the circadian pacemaker-which regulates the timing of sleep, endocrine function, alertness and performance-and the timing of the imposed sleep-wake schedule. Crewmembers of the 105-day simulation study will be required to work one night shift every sixth night. This schedule will likely result in sleep loss and circadian misalignment, especially when lighting conditions are similar to those that crewmembers experience during spaceflight. External mission controllers will work 24-hour shifts, also resulting in both sleep loss and circadian misalignment. It has been well documented in laboratory and field studies that both working the night shift and working extended duration shifts result in decrement alertness, performance and mood. In addition to the negative effects that night shift work has on alertness, performance and mood, shift work causes significant short and long-term health problems. Shift workers, particularly night shift workers who invert their normal sleep/wake schedule, suffer for several reasons. First, their endogenous circadian rhythms and the imposed sleep/work schedule are typically out of phase. This is similar to the experience of jet lag. However, while environment cues (e.g., sunrise, sunset, the timing of meals and sleep) enable travelers to adapt quickly to a new time zone, crewmembers in the 105-day simulation will be unable to do so because they will only spend one night of every five working. When working the night shift, the timing of meals, work, and sleep will therefore be out of phase with the normal entrained phase of the circadian timing system. Ingestion of meals at an inappropriate circadian phase results in impaired metabolism, likely underlying the gastrointestinal and metabolic problems experienced by shift workers. Second, this circadian misalignment leads to a substantial loss of sleep efficiency during the (daytime) sleep period, independent of, and in addition to, environmental obstacles to sleep (e.g., noise, light, other crewmembers). Third, misalignment of circadian phase coupled with sleep loss will each result in deterioration of alertness and impairment of performance during the night. Since these adverse effects are particularly acute on the first night of work, the plan for crewmembers on the Mars 105 mission to work the midnight shift every sixth night will subject them repeatedly to the performance impairments associated with acute circadian misalignment and acute sleep deprivation. Lighting Countermeasure. Our group at the Harvard Medical School has successfully developed and tested effective photic countermeasures to alleviate circadian misalignment and improve alertness, performance and mood in night shift workers. The most effective countermeasure to circadian alignment is appropriately-timed and sufficiently intense light. Light also acutely improves alertness, performance and mood. Most recently it has been reported that short wavelength light has been shown to be most effective for both resetting circadian rhythms and acutely improving performance during night work via antecedent suppression of the soporific hormone melatonin. These photic countermeasures have been tested in individual subjects living in laboratory simulations (Countermeasures readiness level/Technology readiness level 7; Evaluation with human subjects in controlled laboratory simulating operational spaceflight environment). The next critical step is to evaluate our countermeasures in an operational simulation of space flight that includes study of the interaction among crew members in a high fidelity simulation (Countermeasures readiness level/Technology readiness level 8; Validation with human subjects in actual operational spaceflight to demonstrate efficacy and operational feasibility). Adequate sleep and circadian alignment are critical to maintaining the health and performance of expedition mission crewmembers. Testing of the developed lighting countermeasure in a high fidelity operational environment imitating the conditions of a future expedition mission (e.g., to Mars) is critical to ensure countermeasure readiness and to reduce the risk of human performance errors due to factors related to circadian disruption, sleep loss and fatigue. Development and testing of this photic countermeasure for mission controllers working 24-hour shifts will further ensure the success of the future long duration expedition missions.