Understanding the Role of Sleep in Safety-Sensitive Occupations

During a session at SLEEP 2021 entitled "Sleep and Sleep Loss in Soldiers, First Responders, and Flight Crew," investigators presented research outlining the impact of sleep on certain safety-sensitive occupations.

In one study, Michelle E. Stepan, PhD, a postdoctoral researcher at the University of Pittsburgh, and colleagues investigated how the combination of physical exertion and sleep loss affects cognition in firefighters.

“We often think of being a firefighter as one of the most physically demanding professions, but it is also very cognitively demanding. It is important to understand how these demands placed on firefighters affect cognitive functioning, given that it may play a role in the number of injuries and fatal accidents that occur while on the job,” Stepan explained.

To determine the effect of physical exertion on vigilant attention and task-switching among firefighters who underwent sleep deprivation or sleep disruption, researchers recruited 24 healthy young males for a within-subjects crossover design study.

All participants completed 3 lab visits where they underwent scenarios of sleep deprivation, sleep disruption (woken 3 times for 60 minutes each), or normal sleep. The next day, participants completed a 50-minute treadmill exercise task in a heated room while wearing protective clothing, a vigilant attention task (psychomotor vigilance task [PVT]), and a task-switching task 5 to 9 times per visit.

The researchers assessed lapses, defined as reaction times (RT) greater than 500 milliseconds, on the PVT. They also looked at RT and accuracy for task switching for both sleep-deprivation and sleep-disruption conditions and compared findings to those of normal sleep.

Analyses revealed:

• Sleep disruption (P = .001) and sleep deprivation (P <.001) increased lapses
• Both sleep disruption (P = .01) and sleep deprivation (P = .04) increased task-switching RT, and sleep deprivation reduced accuracy (P = .02)
• Only task-switching RT improved immediately after the treadmill exercise task and only for the sleep-deprivation condition (P = .03)
• During recovery, all conditions tended to make fewer lapses (P = .001) and show an increase in task-switching accuracy (P = .02)

“We found that both vigilant attention and task switching performance suffered as a result of sleep loss, whether that was in the form of total sleep deprivation or sleep disruption,” Stepan said. However, results showed “physical exertion did not completely counteract deficits due to sleep loss. So, it is still extremely prudent to exercise caution when operating under a state of sleep loss,” she concluded.

In a separate analysis, the researchers studied the impact of sleep on individuals working in a similarly strenuous environment: the US Army.

Insufficient sleep is often unavoidable during military operations due to a number of reasons, including extended missions or shift work, explained Janna Mantua, PhD, a sleep research scientist at the Walter Reed Army Institute of Research.

“Sleep quality can be further degraded by stress, excess consumption of stimulants such as coffee and energy drinks, and a poor physical sleeping environment,” she explained. “Nevertheless, soldiers must continue to perform their duties even on little to no sleep.”

Previous research has shown single nucleotide polymorphism (SNP) allele variations in several genes are associated with interindividual cognitive resilience to sleep loss. By identifying genetically vulnerable soldiers, the researchers hypothesized better decisions regarding personnel selection or assignment and mission planning can be made.

However, due to high cost and burden, broad genetic testing of soldiers is not currently feasible. To address this knowledge gap, the researchers set out to determine whether a survey on subjective resilience to insufficient sleep “can classify soldiers as vulnerable or resilient in a manner that separates them based on (1) objective performance following sleep loss and (2) the presence of alleles associated with resilience to sleep loss,” Mantua said.

Six SNPs from several genes (COMT, ADORA2A, TNFa, CLOCK, DAT1) were sequenced from 75 male US Army special operations soldiers with a mean age of 26. All participants completed a night of mission-driven total sleep deprivation, followed by tests on psychomotor vigilance, response inhibition, and decision-making.

Following a week of recovery sleep, the Iowa Resilience to Sleeplessness Test (iREST) cognitive subscale—which measures subjective resilience to sleep loss—was also administered. The optimal cutoff score for iREST was 2.5 of 5, which was used to differentiate groups for each of the 3 cognitive tests.

Overall, data showed, “The chi-squared test was significant for the COMT gene, such that 82% of behaviorally vulnerable soldiers had alleles linked with vulnerability compared with 41% of behaviorally genetic soldiers. Similarly, 60% of the soldiers classified by the iREST as behaviorally resilient had alleles linked with resilience compared to 18% of oldiers classified as vulnerable,” the researchers wrote.

Replication and expansion of data can aid workplace personnel decisions or help determine which soldiers need to be educated on the impact of sleep loss, while theoretically, those behaviorally and genetically vulnerable to insufficient sleep may be able to identify themselves using this method, Mantua concluded.

In yet another study on safety-sensitive occupations, Lucia Arsintescu, MD, MA, a senior research associate at San Jose State University, and colleagues sought to evaluate sleep outcomes among cabin crewmembers sleeping in a bunk compared with a high-comfort jump seat during one long-haul route.

“In aviation, many studies have demonstrated how in-flight rest locations influence alertness and performance among pilots. But few studies evaluate cabin crew,” Arsintescu said.

Thirty-one cabin crewmembers with a mean age of 30 flew the same route with a duration of around 10 hours and 41 minutes. Participants were randomly assigned to fly on a plane with a bunk or jump seat for sleeping. At bedtime and upon waking, the individuals completed a sleep diary and, throughout the entirety of the study, wore an Actiwatch (Phillips-Respironics Spectrum).

The bunks used in the study required access to an area physically separated from the flight deck and the passenger cabin, and provides provisions for sound and lighting isolation.

Of the 65 flights included in the analyses, 77% had a bunk while 23% had a jump seat. Data showed:

• Crewmembers obtained a mean (SD) 146.46 (67.20) minutes of rest out of which they slept 125.33 (64.91) minutes in the bunk
• While using the jump seat, crewmembers obtained 169.53 (133.30) minutes of rest out of which they slept 142.92 (149.72) minutes
• When crewmembers slept in the bunk, sleep latency was shorter (13.69 [12.64] minutes) and efficiency was better (76.16% [16.09%]) compared with the jump seat (sleep onset: 16.77 [13.89] minutes; sleep efficiency: 60.64% [17.42%])

Crew members also rated their sleepiness as being significantly higher after sleeping in the jump seat compared with the bunk. “Although it seemed that cabin crew members rested and slept for a longer time when using the jump seat, all the other outcome variables of sleep performance and sleepiness were in favor of bunk sleep,” Arsintescu said.

Due to the COVID-19 pandemic, the study abruptly stopped, and more data are needed to generalize results and provide recommendations to airlines, she concluded.