Circadian misalignment affects sleep and medication use before and during spaceflight

Influence of the spaceflight environment on macrophage lineages

Spaceflight and terrestrial spaceflight analogs can alter immune phenotypes. Macrophages are important immune cells that bridge the innate and adaptive immune systems and participate in immunoregulatory processes of homeostasis. Furthermore, macrophages are critically involved in initiating immunity, defending against injury and infection, and are also involved in immune resolution and wound healing. Heterogeneous populations of macrophage-type cells reside in many tissues and cause a variety of tissue-specific effects through direct or indirect interactions with other physiological systems, including the nervous and endocrine systems. It is vital to understand how macrophages respond to the unique environment of space to safeguard crew members with appropriate countermeasures for future missions in low Earth orbit and beyond. This review highlights current literature on macrophage responses to spaceflight and spaceflight analogs.

Spatially resolved multiomics on the neuronal effects induced by spaceflight in mice

Impairment of the central nervous system (CNS) poses a significant health risk for astronauts during long-duration space missions. In this study, we employed an innovative approach by integrating single-cell multiomics (transcriptomics and chromatin accessibility) with spatial transcriptomics to elucidate the impact of spaceflight on the mouse brain in female mice. Our comparative analysis between ground control and spaceflight-exposed animals revealed significant alterations in essential brain processes including neurogenesis, synaptogenesis and synaptic transmission, particularly affecting the cortex, hippocampus, striatum and neuroendocrine structures. Additionally, we observed astrocyte activation and signs of immune dysfunction. At the pathway level, some spaceflight-induced changes in the brain exhibit similarities with neurodegenerative disorders, marked by oxidative stress and protein misfolding. Our integrated spatial multiomics approach serves as a stepping stone towards understanding spaceflight-induced CNS impairments at the level of individual brain regions and cell types, and provides a basis for comparison in future spaceflight studies. For broader scientific impact, all datasets from this study are available through an interactive data portal, as well as the National Aeronautics and Space Administration (NASA) Open Science Data Repository (OSDR).

Hilaire MA, Kirkley CL, Gregory KB, Clark T, Hanifin JP, Barger LK, Czeisler CA, Brainard GC, Lockley SW, Flynn-Evans EE. The effect of a dynamic lighting schedule on neurobehavioral performance during a 45-day simulated space mission

Study Objectives

We previously reported that during a 45-day simulated space mission, a dynamic lighting schedule (DLS) improved circadian phase alignment and performance assessed once on selected days. This study aimed to evaluate how DLS affected performance on a 5-minute psychomotor vigilance task (PVT) administered multiple times per day on selected days.

Methods

Sixteen crewmembers (37.4 ± 6.7 years; 5F) underwent six cycles of 2 × 8-hour/night followed by 5 × 5-hour/night sleep opportunities. During the DLS (n = 8), daytime white light exposure was blue-enriched (~6000 K; Level 1: 1079, Level 2: 76 melanopic equivalent daytime illuminance (melEDI) lux) and blue-depleted (~3000-4000 K; L1: 21, L2: 2 melEDI lux) 3 hours before bed. In the standard lighting schedule (SLS; n = 8), lighting remained constant (~4500K; L1: 284, L2 62 melEDI lux). Effects of lighting condition (DLS/SLS), sleep condition (5/8 hours), time into mission, and their interactions, and time awake on PVT performance were analyzed using generalized linear mixed models.

Results

The DLS was associated with fewer attentional lapses (reaction time [RT] > 500 milliseconds) compared to SLS. Lapses, mean RT, and 10% fastest/slowest RTs were worse following 5 compared to 8 hours of sleep but not between lighting conditions. There was an effect of time into mission on RTs, likely due to sleep loss. Overall performance differed by time of day, with longer RTs at the beginning and end of the day. There were more lapses and slower RTs in the afternoon in the SLS compared to the DLS condition.

Conclusions

Future missions should incorporate DLS to enhance circadian alignment and performance. This paper is part of the Sleep and Circadian Rhythms: Management of Fatigue in Occupational Settings Collection.

Using single-sample networks to identify the contrasting patterns of gene interactions and reveal the radiation dose-dependent effects in multiple tissues of spaceflight mice

Transcriptome profiles are sensitive to space stressors and serve as valuable indicators of the biological effects during spaceflight. Herein, we transformed the expression profiles into gene interaction patterns by single-sample networks (SSNs) and performed the integrated analysis on the 301 spaceflight and 290 ground control samples, which were obtained from the GeneLab platform. Specifically, an individual SSN was established for each sample. Based on the topological structures of 591 SSNs, the differentially interacted genes (DIGs) were identified between spaceflights and ground controls. The results showed that spaceflight disrupted the gene interaction patterns in mice and resulted in significant enrichment of biological processes such as protein/amino acid metabolism and nucleic acid (DNA/RNA) metabolism (P-value < 0.05). We observed that the mice exposed to radiation doses within the three intervals (4.66-7.14, 7.592-8.295, 8.49-22.099 mGy) exhibited similar gene interaction patterns. Low and medium doses resulted in changes to the circadian rhythm, while the damaging effects on genetic material became more pronounced in higher doses. The gene interaction patterns in response to space stressors varied among different tissues, with the spleen, lung, and skin being the most responsive to space radiation (P-value < 0.01). The changes observed in gene networks during spaceflight conditions might contribute to the development of various diseases, such as mental disorders, depression, and metabolic disorders, among others. Additionally, organisms activated specific gene networks in response to virus reactivation. We identified several hub genes that were associated with circadian rhythms, suggesting that spaceflight could lead to substantial circadian rhythm dysregulation.

Development of optic disc edema during 30 days of hypercapnic head-down tilt bed rest is associated with short sleep duration and blunted temperature amplitude

Sleep and circadian temperature disturbances occur with spaceflight and may, in part, result from the chronically elevated carbon dioxide (CO2) levels on the international space station. Impaired sleep may contribute to decreased glymphatic clearance and, when combined with the chronic headward fluid shift during actual spaceflight or the spaceflight analog head-down tilt bed rest (HDTBR), may contribute to the development of optic disc edema. We determined if strict HDTBR combined with mildly elevated CO2 levels influenced sleep and core temperature and was associated with the development of optic disc edema. Healthy participants (5 females) aged 25-50 yr, underwent 30 days of strict 6° HDTBR with ambient Pco2 = 4 mmHg. Measures of sleep, 24-h core temperature, overnight transcutaneous CO2, and Frisén grade edema were made pre-HDTBR, on HDTBR days 4, 17, 28, and post-HDTBR days 4 and 10. During all HDTBR time points, sleep, core temperature, and overnight transcutaneous CO2 were not different than the pre-HDTBR measurements. However, independent of the HDTBR intervention, the odds ratios {mean [95% confidence interval (CI)]} for developing Frisén grade optic disc edema were statistically significant for each hour below the mean total sleep time (2.2 [1.1-4.4]) and stage 2 nonrapid eye movement (NREM) sleep (4.8 [1.3-18.6]), and above the mean for wake after sleep onset (3.6 [1.2-10.6]) and for each 0.1°C decrease in core temperature amplitude below the mean (4.0 [1.4-11.7]). These data suggest that optic disc edema occurring during HDTBR was more likely to occur in those with short sleep duration and/or blunted temperature amplitude.NEW & NOTEWORTHY We determined that sleep and 24-h core body temperature were unaltered by 30 days exposure to the spaceflight analog strict 6° head-down tilt bed rest (HDTBR) in a 0.5% CO2 environment. However, shorter sleep duration, greater wake after sleep onset, and lower core temperature amplitude present throughout the study were associated with the development of optic disc edema, a key finding of spaceflight-associated neuro-ocular syndrome.

Effects of total sleep deprivation on performance in a manual spacecraft docking task

Sleep deprivation and circadian rhythm disruptions are highly prevalent in shift workers, and also among astronauts. Resulting sleepiness can reduce cognitive performance, lead to catastrophic occupational events, and jeopardize space missions. We investigated whether 24 hours of total sleep deprivation would affect performance not only in the Psychomotor Vigilance Task (PVT), but also in a complex operational task, i.e. simulated manual spacecraft docking. Sixty-two healthy participants completed the manual docking simulation 6df and the PVT once after a night of total sleep deprivation and once after eight hours of scheduled sleep in a counterbalanced order. We assessed the impact of sleep deprivation on docking as well as PVT performance and investigated if sustained attention is an essential component of operational performance after sleep loss. The results showed that docking accuracy decreased significantly after sleep deprivation in comparison to the control condition, but only at difficult task levels. PVT performance deteriorated under sleep deprivation. Participants with larger impairments in PVT response speed after sleep deprivation also showed larger impairments in docking accuracy. In conclusion, sleep deprivation led to impaired 6df performance, which was partly explained by impairments in sustained attention. Elevated motivation levels due to the novelty and attractiveness of the task may have helped participants to compensate for the effects of sleepiness at easier task levels. Continued testing of manual docking skills could be a useful tool both to detect sleep loss-related impairments and assess astronauts' readiness for duty during long-duration missions.

Simulated space environmental factors of weightlessness, noise and low atmospheric pressure differentially affect the diurnal rhythm and the gut microbiome

The circadian clock extensively regulates physiology and behavior. In space, astronauts encounter many environmental factors that are dramatically different from those on Earth; however, the effects of these factors on circadian rhythms and the mechanisms remain largely unknown. The present study aimed to investigate the changes in the mouse diurnal rhythm and gut microbiome under simulated space capsule conditions, including microgravity, noise and low atmospheric pressure (LAP). Noise and LAP were loaded in the capsule while the conditions in the animal room remained constant. The mice in the capsule showed disturbed locomotor rhythms and faster adaptation to a 6-h phase advance. RNA sequencing of hypothalamus samples containing the suprachiasmatic nucleus (SCN) revealed that microgravity simulated by hind limb unloading (HU) and exposure to noise and LAP led to decreases in the quantities of differentially expressed genes (DEGs), including circadian clock genes. Changes in the rhythmicity of genes implicated in pathways of cardiovascular deconditioning and more concentrated phases were found under HU or noise and LAP. Furthermore, 16S rRNA sequencing revealed dysbiosis in the gut microbiome, and noise and LAP may repress the temporal discrepancy in the microbiome community structure induced by microgravity. Changes in diurnal oscillations were observed in a number of gut bacteria with critical physiological consequences on metabolism and immunodefense. We also found that the superimposition of noise and LAP may repress normal changes in global gene expression and adaptation in the gut microbiome. Our data demonstrate that in addition to microgravity, exposure to noise and LAP affect the robustness of circadian rhythms and the community structure of the gut microbiome, and these factors may interfere with each other in their adaptation to respective conditions. These findings are important for furthering our understanding of the alterations in circadian rhythms in the complex environment of space.

Circadian adaptation to night shift work is associated with higher REM sleep duration

OBJECTIVE

To investigate the influence of the degree of circadian adaptation to night work on sleep architecture following night shift.

METHODS

Thirty four night workers (11 females; 33.8 ± 10.1years) completed a simulated night shift following 2-7 typical night shifts. Participants completed a laboratory-based simulated night shift (21:00-07:00 hours), followed by a recovery sleep opportunity (∼09:00-17:00 hours), recorded using polysomnography. Urinary 6-sulphatoxymelatonin (aMT6s) rhythm acrophase was used as a marker of circadian phase. Sleep duration and architecture were compared between individuals with aMT6s acrophase before (unadapted group, n = 22) or after (partially adapted group, n = 12) bedtime.

RESULTS

Bedtime occurred on average 2.16 hours before aMT6s acrophase in the partially adapted group and 3.91 hours after acrophase in the unadapted group. The partially adapted group had more sleep during the week before the simulated night than the unadapted group (6.47 ± 1.02 vs. 5.26 ± 1.48 hours, p = .02). After the simulated night shift, both groups had similar total sleep time (partially adapted: 6.68 ± 0.80 hours, unadapted: 6.63 ± 0.88 hours, p > .05). The partially adapted group had longer total rapid eye movement sleep duration than the unadapted group (106.79 ± 32.05 minutes vs. 77.90 ± 28.86 minutes, p = .01). After 5-hours, rapid eye movement sleep accumulation was higher in the partially adapted compared to the unadapted group (p = .02). Sleep latency and other stages were not affected by circadian adaptation.

DISCUSSION

Partial circadian adaptation to night shift was associated with longer rapid eye movement sleep duration during daytime sleep, highlighting the influence of entrainment between the sleep-wake cycle and the circadian pacemaker in night workers. The findings have important implications for sleep and subsequent alertness associated with shift work.

Sleep-Monitoring Technology Progress and Its Application in Space

INTRODUCTION: Sleep is an indispensable physiological phenomenon. The complexity of sleep and the time it occupies in human life determine that its quality is positively correlated with human health. Since polysomnography was used in spaceflight in 1967, the sleep problem during astronaut flight has been studied in depth for more than 50 yr, and many solutions have been proposed, but astronauts have always had sleep problems during orbital flight. Insufficient sleep and changes in the rhythm of human sleep-wake activity will lead to disturbance of the human body's internal rhythm indicators, which will lead to psychological and emotional fluctuations and reduced cognitive ability, decision-making ability, teamwork, and work performance. NASA has identified operational errors due to sleep deprivation and altered circadian rhythms as an important risk factor in the key biomedical roadmap for long-term flight, so the importance of sleep monitoring in spaceflight is self-evident. On-orbit sleep-monitoring methods include both subjective and objective aspects. We review objective sleep-monitoring technology based on its application, main monitoring physiological indicators, intrusive advantages, and limitations. This paper reviews the subjective and objective sleep evaluation methods for on-orbit applications, summarizes the progress, advantages, and disadvantages of current ground sleep-monitoring technologies and equipment, and looks forward to the application prospects of new sleep-monitoring technologies in spaceflight.Zhang C, Chen Y, Fan Z, Xin B, Wu B, Lv K. Sleep-monitoring technology progress and its application in space. Aerosp Med Hum Perform. 2024; 95(1):37-44.

Effectiveness of caffeine and blue-enriched light on cognitive performance and electroencephalography correlates of alertness in a spaceflight robotics simulation

Human cognitive impairment associated with sleep loss, circadian misalignment and work overload is a major concern in any high stress occupation but has potentially catastrophic consequences during spaceflight human robotic interactions. Two safe, wake-promoting countermeasures, caffeine and blue-enriched white light have been studied on Earth and are available on the International Space Station. We therefore conducted a randomized, placebo-controlled, cross-over trial examining the impact of regularly timed low-dose caffeine (0.3 mg per kg per h) and moderate illuminance blue-enriched white light (~90 lux, ~88 melEDI lux, 6300 K) as countermeasures, separately and combined, in a multi-night simulation of sleep-wake shifts experienced during spaceflight among 16 participants (7 F, ages 26-55). We find that chronic administration of low-dose caffeine improves subjective and objective correlates of alertness and performance during an overnight work schedule involving chronic sleep loss and circadian misalignment, although we also find that caffeine disrupts subsequent sleep. We further find that 90 lux of blue-enriched light moderately reduces electroencephalogram (EEG) power in the theta and delta regions, which are associated with sleepiness. These findings support the use of low-dose caffeine and potentially blue-enriched white light to enhance alertness and performance among astronauts and shiftworking populations.

Sleep disruption, use of sleep-promoting medication and circadian desynchronization in spaceflight crewmembers: Evidence in low-Earth orbit and concerns for future deep-space exploration missions

Introduction

The spaceflight environment presents unique demands on human physiology; among those demands, is sleep. Sleep loss and circadian desynchronization is a major concern for future deep- exploration plans, including long-term crewed missions to the Moon and Mars.

Aims

Analyze evidence of sleep disruption in crewmembers during low-Earth orbit missions, identify the use of sleep-promoting medication among crewmembers and deepen the comprehension of challenges to sleep physiology for future missions to the Moon and Mars.

Results

Evidence consistently indicates a loss of sleep and circadian rhythm disruption during low-Earth orbit missions. Sleep duration is shortened especially the night before a critical operation and during circadian-misaligned sleep episodes. The prevalence of sleep-promoting medication ranges between 71% and 78%; medication is more frequently taken on circadian-misaligned sleep episodes. Regarding the Moon, Apollo astronauts had variable sleep duration. For some, sleep was restful while others had poor-quality sleep. Many reported fatigue and errors due to the lack of rest. A loss of the 24-h light/dark might be expected due to the Moon's complex illumination characteristics. Regarding Mars, one main challenge will consist in synchronizing the circadian clock to a Martian day (24.65 h).

Healthy sleep practices for shift workers: consensus sleep hygiene guidelines using a Delphi methodology

STUDY OBJECTIVES

The unique requirements of shift work, such as sleeping and working at variable times, mean that current sleep hygiene guidelines may be inappropriate for shift workers. Current guidelines may also contradict fatigue management advice (e.g. advising against daytime napping). The present study utilized a Delphi methodology to determine expert opinion regarding the applicability of current guidelines for shift workers, the appropriateness of the term "sleep hygiene," and develop tailored guidelines for shift workers.

METHODS

The research team reviewed current guidelines and existing evidence to draft tailored guidelines. Seventeen individual guidelines, covering sleep scheduling, napping, sleep environment, bedtime routine, substances, light exposure, diet, and exercise were drafted. Experts from sleep, shift work, and occupational health fields (n = 155) were invited to review the draft guidelines using a Delphi methodology. In each round, experts voted on individual guidelines, with 70% agreement considered consensus. Where consensus was not reached, written feedback from experts was discussed and incorporated into subsequent iterations.

RESULTS

Of the experts invited, 68 (44%) agreed to participate, with 55 (35%) completing the third (final) round. Most experts (84%) agreed that tailored guidelines were required for shift workers. Consensus was reached on all guidelines after three rounds. One additional guideline (sleep inertia) and an introductory statement were developed, resulting in a final set of 18 individual guidelines, termed "healthy sleep practices for shift workers."

CONCLUSIONS

This is the first study to develop tailored sleep hygiene guidelines for shift workers. Future research should investigate the acceptability and effectiveness of these guidelines amongst shift workers.

Independent and joint trajectories of depression and anxiety symptoms among Chinese male sailors throughout a prolonged non-24-h rotating shift schedule at sea: a parallel-process growth mixture modeling approach

BACKGROUND

The predictive and protective effect of hardiness on mental health remains unclear among shift workers on non-24-h working schedules. The present study aimed to investigate the independent and joint trajectories of depression and anxiety symptoms and the role of hardiness during a prolonged period of non-24-h shift working schedule.

METHODS

Four hundred nine Chinese male sailors (working on 18-h watchstanding schedule) were recruited and completed all 5-wave tests through online questionnaires (at Day 1, 14, 28, 42, 55, respectively) during a 55-day sailing. The questionnaires included sociodemographic variables, hardiness, depression and anxiety symptoms. Independent and joint trajectories of depression and anxiety symptoms were estimated by latent growth mixture models. The effect of hardiness on trajectories was examined by logistic regression models.

RESULTS

2 and 3 latent trajectories were identified for depression and anxiety symptoms, respectively. Based on initial levels and development trends, 3 distinct joint trajectories of depression and anxiety were identifed and named as: "Low-Inverted U" group (73.6%), "Moderate-Deterioration" group (6.9%), and "High-Stable" group (9.5%). Sailors with higher levels of hardiness were more likely to follow the "Low-Inverted U" trajectory of depression and anxiety symptoms (all p < 0.001).

CONCLUSIONS

There existed individual differences in the trajectories of depression and anxiety. Hardiness may have a protective effect that can prevent and alleviate depression and anxiety symptoms. Therefore, hardiness-based intervention programs are encouraged among the shift workers on non-24-h working and rest schedules.

Long-term spaceflight composite stress induces depression and cognitive impairment in astronauts-insights from neuroplasticity

The environment on the space station is quite unique compared to Earth, which is a composite of multiple stressors, such as microgravity, isolation, confinement, noise, circadian rhythm disturbance, and so on. During prolonged space missions, astronauts have to stay in such extreme environments for long periods, which could induce adverse effects on both their physical and mental health. In some circumstances, this kind of long-term spaceflight composite stress (LSCS) could also induce depression and cognitive impairment in various ways, including dysregulating the neuroplasticity of the brains of astronauts, which should be attached to great importance. Here, we have comprehensively reviewed the impact of individual and combined stressors on depression and cognitive function during long-term spaceflight, explained the underlying mechanisms of those effects from the perspective of neuroplasticity, and current countermeasures for mitigating these challenges. This review provides insights into LSCS and potential neuroplasticity mechanisms, current with potentially great impact for understanding and mitigating the mental health risks and traumas of career astronauts and space tourists.

Spaceflight-Induced Gene Expression Profiles in the Mouse Brain Are Attenuated by Treatment with the Antioxidant BuOE

The demands of deep space pose a health risk to the central nervous system that has long been a concern when sending humans to space. While little is known about how spaceflight affects transcription spatially in the brain, a greater understanding of this process has the potential to aid strategies that mitigate the effects of spaceflight on the brain. Therefore, we performed GeoMx Digital Spatial Profiling of mouse brains subjected to either spaceflight or grounded controls. Four brain regions were selected: Cortex, Frontal Cortex, Corunu Ammonis I, and Dentate Gyrus. Antioxidants have emerged as a potential means of attenuating the effects of spaceflight, so we treated a subset of the mice with a superoxide dismutase mimic, MnTnBuOE-2-PyP 5+ (BuOE). Our analysis revealed hundreds of differentially expressed genes due to spaceflight in each of the four brain regions. Both common and region-specific transcriptomic responses were observed. Metabolic pathways and pathways sensitive to oxidative stress were enriched in the four brain regions due to spaceflight. These findings enhance our understanding of brain regional variation in susceptibility to spaceflight conditions. BuOE reduced the transcriptomic effects of spaceflight at a large number of genes, suggesting that this compound may attenuate oxidative stress-induced brain damage caused by the spaceflight environment.

Methods for assessing change in brain plasticity at night and psychological resilience during daytime between repeated long-duration space missions

This study was designed to examine the feasibility of analyzing heart rate variability (HRV) data from repeat-flier astronauts at matching days on two separate missions to assess any effect of repeated missions on brain plasticity and psychological resilience, as conjectured by Demertzi. As an example, on the second mission of a healthy astronaut studied about 20 days after launch, sleep duration lengthened, sleep quality improved, and spectral power (ms²) co-varying with activity of the salience network (SN) increased at night. HF-component (0.15-0.50 Hz) increased by 61.55%, and HF-band (0.30-0.40 Hz) by 92.60%. Spectral power of HRV indices during daytime, which correlate negatively with psychological resilience, decreased, HF-component by 22.18% and HF-band by 37.26%. LF-component and LF-band, reflecting activity of the default mode network, did not change significantly. During the second mission, 24-h acrophases of HRV endpoints did not change but the 12-h acrophase of TF-HRV did (P < 0.0001), perhaps consolidating the circadian system to help adapt to space by taking advantage of brain plasticity at night and psychological resilience during daytime. While this N-of-1 study prevents drawing definitive conclusions, the methodology used herein to monitor markers of brain plasticity could pave the way for further studies that could add to the present results.

The value of a spaceflight clinical decision support system for earth-independent medical operations

As NASA prepares for crewed lunar missions over the next several years, plans are also underway to journey farther into deep space. Deep space exploration will require a paradigm shift in astronaut medical support toward progressively earth-independent medical operations (EIMO). The Exploration Medical Capability (ExMC) element of NASA's Human Research Program (HRP) is investigating the feasibility and value of advanced capabilities to promote and enhance EIMO. Currently, astronauts rely on real-time communication with ground-based medical providers. However, as the distance from Earth increases, so do communication delays and disruptions. Moreover, resupply and evacuation will become increasingly complex, if not impossible, on deep space missions. In contrast to today's missions in low earth orbit (LEO), where most medical expertise and decision-making are ground-based, an exploration crew will need to autonomously detect, diagnose, treat, and prevent medical events. Due to the sheer amount of pre-mission training required to execute a human spaceflight mission, there is often little time to devote exclusively to medical training. One potential solution is to augment the long duration exploration crew's knowledge, skills, and abilities with a clinical decision support system (CDSS). An analysis of preliminary data indicates the potential benefits of a CDSS to mission outcomes when augmenting cognitive and procedural performance of an autonomous crew performing medical operations, and we provide an illustrative scenario of how such a CDSS might function.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

Long-term human spaceflight and inflammaging: Does it promote aging?

Spaceflight and its associated stressors, such as microgravity, radiation exposure, confinement, circadian derailment and disruptive workloads represent an unprecedented type of exposome that is entirely novel from an evolutionary stand point. Within this perspective, we aimed to review the effects of prolonged spaceflight on immune-neuroendocrine systems, brain and brain-gut axis, cardiovascular system and musculoskeletal apparatus, highlighting in particular the similarities with an accelerated aging process. In particular, spaceflight-induced muscle atrophy/sarcopenia and bone loss, vascular and metabolic changes, hyper and hypo reaction of innate and adaptive immune system appear to be modifications shared with the aging process. Most of these modifications are mediated by molecular events that include oxidative and mitochondrial stress, autophagy, DNA damage repair and telomere length alteration, among others, which directly or indirectly converge on the activation of an inflammatory response. According to the inflammaging theory of aging, such an inflammatory response could be a driver of an acceleration of the normal, physiological rate of aging and it is likely that all the systemic modifications in turn lead to an increase of inflammaging in a sort of vicious cycle. The most updated countermeasures to fight these modifications will be also discussed in the light of their possible application not only for astronauts' benefit, but also for older adults on the ground.

Profiling rhythmicity of bile salt hydrolase activity in the gut lumen with a rapid fluorescence assay

Diurnal rhythmicity of cellular function is key to survival for most organisms on Earth. Many circadian functions are driven by the brain, but regulation of a separate set of peripheral rhythms remains poorly understood. The gut microbiome is a potential candidate for regulation of host peripheral rhythms, and this study sought to specifically examine the process of microbial bile salt biotransformation. To enable this work, an assay for bile salt hydrolase (BSH) that could work with small quantities of stool samples was necessary. Using a turn-on fluorescence probe, we developed a rapid and inexpensive assay to detect BSH enzyme activity with concentrations as low as 6-25 μM, which is considerably more robust than prior approaches. We successfully applied this rhodamine-based assay to detect BSH activity in a wide range of biological samples such as recombinant protein, whole cells, fecal samples, and gut lumen content from mice. We were able to detect significant BSH activity in small amounts of mouse fecal/gut content (20-50 mg) within 2 h, which illustrates its potential for use in various biological/clinical applications. Using this assay, we investigated the diurnal fluctuations of BSH activity in the large intestine of mice. By using time restricted feeding conditions, we provided direct evidence of 24 h rhythmicity in microbiome BSH activity levels and showed that this rhythmicity is influenced by feeding patterns. Our novel function-centric approach has potential to aid in the discovery of therapeutic, diet, or lifestyle interventions for correction of circadian perturbations linked to bile metabolism.

Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure

Exposure to the space environment induces a number of pathophysiological outcomes in astronauts, including bone demineralization, sleep disorders, circadian clock dysregulation, cardiovascular and metabolic dysfunction, and reduced immune system function. A recent report describing experiments aboard the Space Shuttle mission, STS-132, showed that the level of melatonin, a hormone that provides the biochemical signal of darkness, was decreased during microgravity in an in vitro culture model. Additionally, abnormal lighting conditions in outer space, such as low light intensity in orbital spacecraft and the altered 24-h light-dark cycles, may result in the dysregulation of melatonin rhythms and the misalignment of the circadian clock from sleep and work schedules in astronauts. Studies on Earth have demonstrated that melatonin regulates various physiological functions including bone metabolism. These data suggest that the abnormal regulation of melatonin in outer space may contribute to pathophysiological conditions of astronauts. In addition, experiments with high-linear energy transfer radiation, a ground-based model of space radiation, showed that melatonin may serve as a protectant against space radiation. Gene expression profiling using an in vitro culture model exposed to space flight during the STS-132 mission, showed that space radiation alters the expression of DNA repair and oxidative stress response genes, indicating that melatonin counteracts the expression of these genes responsive to space radiation to promote cell survival. These findings implicate the use of exogenous melatonin and the regulation of endogenous melatonin as countermeasures for the physiological consequences of space flight.

Limits of entrainment of circadian neuronal networks

Circadian rhythmicity lies at the center of various important physiological and behavioral processes in mammals, such as sleep, metabolism, homeostasis, mood changes, and more. Misalignment of intrinsic neuronal oscillations with the external day-night cycle can disrupt such processes and lead to numerous disorders. In this work, we computationally determine the limits of circadian synchronization to external light signals of different frequency, duty cycle, and simulated amplitude. Instead of modeling circadian dynamics with generic oscillator models (e.g., Kuramoto-type), we use a detailed computational neuroscience model, which integrates biomolecular dynamics, neuronal electrophysiology, and network effects. This allows us to investigate the effect of small drug molecules, such as Longdaysin, and connect our results with experimental findings. To combat the high dimensionality of such a detailed model, we employ a matrix-free approach, while our entire algorithmic pipeline enables numerical continuation and construction of bifurcation diagrams using only direct simulation. We, thus, computationally explore the effect of heterogeneity in the circadian neuronal network, as well as the effect of the corrective therapeutic intervention of Longdaysin. Last, we employ unsupervised learning to construct a data-driven embedding space for representing neuronal heterogeneity.

Effects of dynamic lighting on circadian phase, self-reported sleep and performance during a 45-day space analog mission with chronic variable sleep deficiency

Spaceflight exposes crewmembers to circadian misalignment and sleep loss, which impair cognition and increase the risk of errors and accidents. We compared the effects of an experimental dynamic lighting schedule (DLS) with a standard static lighting schedule (SLS) on circadian phase, self-reported sleep and cognition during a 45-day simulated space mission. Sixteen participants (mean age [±SD] 37.4 ± 6.7 years; 5 F; n = 8/lighting condition) were studied in four-person teams at the NASA Human Exploration Research Analog. Participants were scheduled to sleep 8 h/night on two weekend nights, 5 h/night on five weekday nights, repeated for six 7-day cycles, with scheduled waketime fixed at 7:00 a.m. Compared to the SLS where illuminance and spectrum remained constant during wake (~4000K), DLS increased the illuminance and short-wavelength (blue) content of white light (~6000K) approximately threefold in the main workspace (Level 1), until 3 h before bedtime when illuminance was reduced by ~96% and the blue content also reduced throughout (~4000K × 2 h, ~3000K × 1 h) until bedtime. The average (±SE) urinary 6-sulphatoxymelatonin (aMT6s) acrophase time was significantly later in the SLS (6.22 ± 0.34 h) compared to the DLS (4.76 ± 0.53 h) and more variable in SLS compared to DLS (37.2 ± 3.6 min vs. 28.2 ± 2.4 min, respectively, p = .04). Compared to DLS, self-reported sleep was more frequently misaligned relative to circadian phase in SLS RR: 6.75, 95% CI 1.55-29.36, p = .01), but neither self-reported sleep duration nor latency to sleep was different between lighting conditions. Accuracy in the abstract matching and matrix reasoning tests were significantly better in DLS compared to SLS (false discovery rate-adjusted p ≤ .04). Overall, DLS alleviated the drift in circadian phase typically observed in space analog studies and reduced the prevalence of self-reported sleep episodes occurring at an adverse circadian phase. Our results support incorporating DLS in future missions, which may facilitate appropriate circadian alignment and reduce the risk of sleep disruption.

The role of circadian phase in sleep and performance during Antarctic winter expeditions

The Antarctic environment presents an extreme variation in the natural light-dark cycle which can cause variability in the alignment of the circadian pacemaker with the timing of sleep, causing sleep disruption, and impaired mood and performance. This study assessed the incidence of circadian misalignment and the consequences for sleep, cognition, and psychological health in 51 over-wintering Antarctic expeditioners (45.6 ± 11.9 years) who completed daily sleep diaries, and monthly performance tests and psychological health questionnaires for 6 months. Circadian phase was assessed via monthly 48-h urine collections to assess the 6-sulphatoxymelatonin (aMT6s) rhythm. Although the average individual sleep duration was 7.2 ± 0.8 h, there was substantial sleep deficiency with 41.4% of sleep episodes <7 h and 19.1% <6 h. Circadian phase was highly variable and 34/50 expeditioners had sleep episodes that occurred at an abnormal circadian phase (acrophase outside of the sleep episode), accounting for 18.8% (295/1565) of sleep episodes. Expeditioners slept significantly less when misaligned (6.1 ± 1.3 h), compared with when aligned (7.3 ± 1.0 h; p < .0001). Performance and mood were worse when awake closer to the aMT6s peak and with increased time awake (all p < .0005). This research highlights the high incidence of circadian misalignment in Antarctic over-wintering expeditioners. Similar incidence has been observed in long-duration space flight, reinforcing the fidelity of Antarctica as a space analog. Circadian misalignment has considerable safety implications, and potentially longer term health risks for other circadian-controlled physiological systems. This increased risk highlights the need for preventative interventions, such as proactively planned lighting solutions, to ensure circadian alignment during long-duration Antarctic and space missions.

Hilaire MA, Grant LK, Barger LK, Brainard GC, Czeisler CA, Klerman EB, Lockley SW. Dynamic lighting schedules to facilitate circadian adaptation to shifted timing of sleep and wake

Circadian adaptation to shifted sleep/wake schedules may be facilitated by optimizing the timing, intensity and spectral characteristics of light exposure, which is the principal time cue for mammalian circadian pacemaker, and possibly by strategically timing nonphotic time cues such as exercise. Therefore, circadian phase resetting by light and exercise was assessed in 44 healthy participants (22 females, mean age [±SD] 36.2 ± 9.2 years), who completed 8-day inpatient experiments simulating night shiftwork, which included either an 8 h advance or 8 h delay in sleep/wake schedules. In the advance protocol (n = 18), schedules were shifted either gradually (1.6 h/day across 5 days) or abruptly (slam shift, 8 h in 1 day and maintained across 5 days). Both advance protocols included a dynamic lighting schedule (DLS) with 6.5 h exposure of blue-enriched white light (704 melanopic equivalent daylight illuminance [melEDI] lux) during the day and dimmer blue-depleted light (26 melEDI lux) for 2 h immediately before sleep on the shifted schedule. In the delay protocol (n = 26), schedules were only abruptly delayed but included four different lighting conditions: (1) 8 h continuous room-light control; (2) 8 h continuous blue-enriched light; (3) intermittent (7 × 15 min pulses/8 h) blue-enriched light; (4) 8 h continuous blue-enriched light plus moderate intensity exercise. In the room-light control, participants received dimmer white light for 30 min before bedtime, whereas in the other three delay protocols participants received dimmer blue-depleted light for 30 min before bedtime. Both the slam and gradual advance protocols induced similar shifts in circadian phase (3.28 h ± 0.37 vs. 2.88 h ± 0.31, respectively, p = .43) estimated by the change in the timing of timing of dim light melatonin onset. In the delay protocol, the continuous 8 h blue-enriched exposure induced significantly larger shifts than the room light control (-6.59 h ± 0.43 vs. -4.74 h ± 0.62, respectively, p = .02). The intermittent exposure induced ~60% of the shift (-3.90 h ± 0.62) compared with 8 h blue-enriched continuous light with only 25% of the exposure duration. The addition of exercise to the 8 h continuous blue-enriched light did not result in significantly larger phase shifts (-6.59 h ± 0.43 vs. -6.41 h ± 0.69, p = .80). Collectively, our results demonstrate that, when attempting to adapt to an 8 h overnight work shift, delay shifts are more successful, particularly when accompanied by a DLS with high-melanopic irradiance light stimulus during wake.

Dynamic ensemble prediction of cognitive performance in spaceflight

During spaceflight, astronauts face a unique set of stressors, including microgravity, isolation, and confinement, as well as environmental and operational hazards. These factors can negatively impact sleep, alertness, and neurobehavioral performance, all of which are critical to mission success. In this paper, we predict neurobehavioral performance over the course of a 6-month mission aboard the International Space Station (ISS), using ISS environmental data as well as self-reported and cognitive data collected longitudinally from 24 astronauts. Neurobehavioral performance was repeatedly assessed via a 3-min Psychomotor Vigilance Test (PVT-B) that is highly sensitive to the effects of sleep deprivation. To relate PVT-B performance to time-varying and discordantly-measured environmental, operational, and psychological covariates, we propose an ensemble prediction model comprising of linear mixed effects, random forest, and functional concurrent models. An extensive cross-validation procedure reveals that this ensemble outperforms any one of its components alone. We also identify the most important predictors of PVT-B performance, which include an individual's previous PVT-B performance, reported fatigue and stress, and temperature and radiation dose. This method is broadly applicable to settings where the main goal is accurate, individualized prediction of human behavior involving a mixture of person-level traits and irregularly measured time series.

The submariners' sleep study. A field investigation of sleep and circadian hormones during a 67-days submarine mission with a strict 6h-on/6h-off watch routine

The submarine working and living environment is an isolated, confined, and extreme (ICE) environment where a continuous on-watch is required to fulfill the tactical objectives. The current study examined whether a physiological and behavioral adjustment to an operational watch standing scheme occurred in terms of hormonal secretion (i.e., melatonin and cortisol) and sleep during a 67-days undersea mission. The crew followed a strict scheme of watch-on blocks at 0:00-06:00 h and at 12:00-18:00 h (group 1, diurnal sleep group) or watch-on blocks at 06:00-12:00 h and 18:00-24:00 h (group 2, nocturnal sleep group). We sampled saliva during the operational blocks over a 24h period at day 55 of the mission and collected sleep actigraphy data during the entire mission in 10 participants. Sleep showed a biphasic split pattern with significantly unequal distributions of total sleep time (TST) and sleep efficiency (SE) between the two sleeping blocks, i.e., one long and one short sleep bout. Melatonin secretion showed no adjustment at the end of the mission to the watch standing blocks, following an endogenous circadian rhythm independent from the social zeitgebers with indications of a phase shift. Cortisol secretion however matched the biphasic work-sleep shift routine. Human physiology does not fully obey operational needs and there are differences in adjustment between melatonin and cortisol. A watch standing schedule that provides a balance between physiology and operationality still needs to be established. The potential adaptation effects of bright light therapy and melatonin supplementation should be investigated in future research.

Sleep deficiency in spaceflight is associated with degraded neurobehavioral functions and elevated stress in astronauts on six-month missions aboard the International Space Station

Astronauts are required to maintain optimal neurobehavioral functioning despite chronic exposure to the stressors and challenges of spaceflight. Sleep of adequate quality and duration is fundamental to neurobehavioral functioning, however astronauts commonly experience short sleep durations in spaceflight (<6 h). As humans embark on long-duration space exploration missions, there is an outstanding need to identify the consequences of sleep deficiency in spaceflight on neurobehavioral functions. Therefore, we conducted a longitudinal study that examined the sleep-wake behaviors, neurobehavioral functions, and ratings of stress and workload of N = 24 astronauts before, during, and after 6-month missions aboard the International Space Station (ISS). The computerized, Reaction SelfTest (RST), gathered astronaut report of sleep-wake behaviors, stress, workload, and somatic behavioral states; the RST also objectively assessed vigilant attention (i.e. Psychomotor Vigilance Test-Brief). Data collection began 180 days before launch, continued every 4 days in-flight aboard the ISS, and up to 90 days post-landing, which produced N = 2,856 RSTs. Consistent with previous ISS studies, astronauts reported sleeping ~6.5 h in-flight. The adverse consequences of short sleep were observed across neurobehavioral functions, where sleep durations <6 h were associated with significant reductions in psychomotor response speed, elevated stress, and higher workload. Sleep durations <5 h were associated with elevated negative somatic behavioral states. Furthermore, longer sleep durations had beneficial effects on astronaut neurobehavioral functions. Taken together, our findings highlight the importance of sleep for the maintenance of neurobehavioral functioning and as with humans on Earth, astronauts would likely benefit from interventions that promote sleep duration and quality.

Altered sleep spindles and slow waves during space shuttle missions

Sleep deficiencies and associated performance decrements are common among astronauts during spaceflight missions. Previously, sleep in space was analyzed with a focus on global measures while the intricate structure of sleep oscillations remains largely unexplored. This study extends previous findings by analyzing how spaceflight affects characteristics of sleep spindles and slow waves, two sleep oscillations associated with sleep quality and quantity, in four astronauts before, during and after two Space Shuttle missions. Analysis of these oscillations revealed significantly increased fast spindle density, elevated slow spindle frequency, and decreased slow wave amplitude in space compared to on Earth. These results reflect sleep characteristics during spaceflight on a finer electrophysiological scale and provide an opportunity for further research on sleep in space.

Neuro-consequences of the spaceflight environment

As human space exploration advances to establish a permanent presence beyond the Low Earth Orbit (LEO) with NASA's Artemis mission, researchers are striving to understand and address the health challenges of living and working in the spaceflight environment. Exposure to ionizing radiation, microgravity, isolation and other spaceflight hazards pose significant risks to astronauts. Determining neurobiological and neurobehavioral responses, understanding physiological responses under Central Nervous System (CNS) control, and identifying putative mechanisms to inform countermeasure development are critically important to ensuring brain and behavioral health of crew on long duration missions. Here we provide a detailed and comprehensive review of the effects of spaceflight and of ground-based spaceflight analogs, including simulated weightlessness, social isolation, and ionizing radiation on humans and animals. Further, we discuss dietary and non-dietary countermeasures including artificial gravity and antioxidants, among others. Significant future work is needed to ensure that neural, sensorimotor, cognitive and other physiological functions are maintained during extended deep space missions to avoid potentially catastrophic health and safety outcomes.

Gastrodia elata blume ameliorates circadian rhythm disorder-induced mice memory impairment

Circadian rhythm disorder (CRD) in space flight can lead to memory impairment, performance decrements and adverse health outcomes, the main manifestations of which are circadian desynchronization, sleep loss and insomnia. Sleep deprivation (SD) provide the means to evaluate these effects and the risks associated with CRD on ground. Gastrodia elata Blume (GEB) has beneficial effects on the treatment of sleep disturbances and memory loss. Fresh GEB (FG), an unprocessed raw tuber of GEB, has been used as functional health food in Asian countries for a long time. However, the research report of FG to ameliorate memory impairment caused by insomnia or lack of sleep is meager. In this study, ICR male mice were sleep-deprived continuously and water extract of FG (WFG) was orally administrated (3 and 9 g/kg/d, i.g) during the SD process lasted for 25 days, except control and model groups gavage administration with water, positive control group with modafinil (MOD, 0.1 g/kg/d, i.g). We studied the effect of WFG on CRD-induced learning and memory impairment using a set of behavioral analyses including the object location recognition test (OLRT), novel object recognition test (NORT), and the passive avoidance test (PAT). In addition, oxidative stress parameters were assessed by measuring the malondialdehyde (MDA) and superoxide dismutase (SOD) reactivity in serum and hippocampus. Our results revealed that SD decreased discrimination index (DI) in OLRT and NORT, with shorter latency into the dark chamber in PAT. Both WFG and MOD treatment can reverse these changes (P < 0.05). We concluded that WFG treatment improve CRD-induced learning and memory impairment and oxidative stress damage which makes FG a promising candidate as herbal health product of memory decline in CRD.

The Human Sleep Paradox: The Unexpected Sleeping Habits of Homo sapiens

The human sleep pattern is paradoxical. Sleep is vital for optimal physical and cognitive performance, yet humans sleep the least of all primates. In addition, consolidated and continuous monophasic sleep is evidently advantageous, yet emerging comparative data sets from small-scale societies show that the phasing of the human pattern of sleep–wake activity is highly variable and characterized by significant nighttime activity. To reconcile these phenomena, the social sleep hypothesis proposes that extant traits of human sleep emerged because of social and technological niche construction. Specifically, sleep sites function as a type of social shelter by way of an extended structure of social groups that increases fitness. Short, high-quality, and flexibly timed sleep likely originated as a response to predation risks while sleeping terrestrially. This practice may have been a necessary preadaptation for migration out of Africa and for survival in ecological niches that penetrate latitudes with the greatest seasonal variation in light and temperature on the planet.

Brains in space: the importance of understanding the impact of long-duration spaceflight on spatial cognition and its neural circuitry

Fifty years after the first humans stepped on the Moon, space faring nations have entered a new era of space exploration. NASA’s reference mission to Mars is expected to comprise 1100 days. Deep space exploratory class missions could even span decades. They will be the most challenging and dangerous expeditions in the history of human spaceflight and will expose crew members to unprecedented health and performance risks. The development of adverse cognitive or behavioral conditions and psychiatric disorders during those missions is considered a critical and unmitigated risk factor. Here, we argue that spatial cognition, i.e., the ability to encode representations about self-to-object relations and integrate this information into a spatial map of the environment, and their neural bases will be highly vulnerable during those expeditions. Empirical evidence from animal studies shows that social isolation, immobilization, and altered gravity can have profound effects on brain plasticity associated with spatial navigation. We provide examples from historic spaceflight missions, spaceflight analogs, and extreme environments suggesting that spatial cognition and its neural circuitry could be impaired during long-duration spaceflight, and identify recommendations and future steps to mitigate these risks.

Bellagio II Report: Terrestrial Applications of Space Medicine Research

AbstractINTRODUCTION: For over 50 yr, investigators have studied the physiological adaptations of the human system during short- and long-duration spaceflight exposures. Much of the knowledge gained in developing health countermeasures for astronauts onboard the International Space Station demonstrate terrestrial applications. To date, a systematic process for translating these space applications to terrestrial human health has yet to be defined.METHODS: In the summer of 2017, a team of 38 international scientists launched the Bellagio ll Summit Initiative. The goals of the Summit were: 1) To identify space medicine findings and countermeasures with highest probability for future terrestrial applications; and 2) To develop a roadmap for translation of these countermeasures to future terrestrial application. The team reviewed public domain literature, NASA databases, and evidence books within the framework of the five-stage National Institutes of Health (NIH) translation science model, and the NASA two-stage translation model. Teams then analyzed and discussed interdisciplinary findings to determine the most significant evidence-based countermeasures sufficiently developed for terrestrial application.RESULTS: Teams identified published human spaceflight research and applied translational science models to define mature products for terrestrial clinical practice.CONCLUSIONS: The Bellagio ll Summit identified a snapshot of space medicine research and mature science with the highest probability of translation and developed a Roadmap of terrestrial application from space medicine-derived countermeasures. These evidence-based findings can provide guidance regarding the terrestrial applications of best practices, countermeasures, and clinical protocols currently used in spaceflight.Sides MB, Johnston SL III, Sirek A, Lee PH, Blue RS, Antonsen EL, Basner M, Douglas GL, Epstein A, Flynn-Evans EE, Gallagher MB, Hayes J, Lee SMC, Lockley SW, Monseur B, Nelson NG, Sargsyan A, Smith SM, Stenger MB, Stepanek J, Zwart SR; Bellagio II Team. Bellagio II report: terrestrial applications of space medicine research. Aerosp Med Hum Perform. 2021; 92(8):650669.

Alterations in the activity and sleep of Drosophila melanogaster under simulated microgravity

This study aimed to investigate alterations in the activity and sleep of Drosophila melanogaster under simulated microgravity, which was implemented through the random positioning machine, while different light conditions (normal photoperiod and constant dark) were set. Fruit flies of different strains and sexes were treated for 3 days, and activity and sleep were monitored using the Drosophila Activity Monitoring System. After 3 days of treatment, fruit flies were sampled to detect the relative expression levels of the major clock genes and some neurotransmitter-related genes. The results showed that for the normal photoperiod (LD) condition, the activity increased and sleep decreased under simulated microgravity, while for the constant dark (DD) condition, the activity and sleep rhythms appeared disordered and the activity increased, thus decreasing the likelihood of waking up during the day. Light conditions, strains, and sexes, individually or in combination, had impacts on the simulated microgravity effects on behaviors. The clock genes and neurotransmitter-related genes had different degrees of response among sexes and strains, although the overall changes were slight. The results indicated that the normal photoperiod could ease the effects of simulated microgravity on fruit flies' activity and sleep and possible unidentified pathways involved in the regulatory mechanism need further exploration. This study is expected to provide ideas and references for studying the effects of microgravity on space life science.

Astronauts well-being and possibly anti-aging improved during long-duration spaceflight

This study assesses how circadian rhythms of heart rate (HR), HR variability (HRV) and activity change during long-term missions in space and how they relate to sleep quality. Ambulatory 48-h ECG and 96-h actigraphy were performed four times on ten healthy astronauts (44.7 ± 6.9 years; 9 men): 120.4 ± 43.7 days (Before) launch; 21.1 ± 2.5 days (ISS01) and 143.0 ± 27.1 days (ISS02) after launch; and 86.6 ± 40.6 days (After) return to Earth. Sleep quality was determined by sleep-related changes in activity, RR-intervals, HRV HF- and VLF-components and LF-band. The circadian amplitude of HR (HR-A) was larger in space (ISS01: 12.54, P = 0.0099; ISS02: 12.77, P = 0.0364) than on Earth (Before: 10.90; After: 10.55 bpm). Sleep duration in space (ISS01/ISS02) increased in 3 (Group A, from 370.7 to 388.0/413.0 min) and decreased in 7 (Group B, from 454.0 to 408.9/381.6 min) astronauts. Sleep quality improved in Group B from 7.07 to 8.36 (ISS01) and 9.36 (ISS02, P = 0.0001). Sleep-related parasympathetic activity increased from 55.2% to 74.8% (pNN50, P = 0.0010) (ISS02). HR-A correlated with the 24-h (r = 0.8110, P = 0.0044), 12-h (r = 0.6963, P = 0.0253), and 48-h (r = 0.6921, P = 0.0266) amplitudes of the magnetic declination index. These findings suggest associations of mission duration with increased well-being and anti-aging benefitting from magnetic fluctuations.

Fundamental Biological Features of Spaceflight: Advancing the Field to Enable Deep-Space Exploration

Research on astronaut health and model organisms have revealed six features of spaceflight biology that guide our current understanding of fundamental molecular changes that occur during space travel. The features include oxidative stress, DNA damage, mitochondrial dysregulation, epigenetic changes (including gene regulation), telomere length alterations, and microbiome shifts. Here we review the known hazards of human spaceflight, how spaceflight affects living systems through these six fundamental features, and the associated health risks of space exploration. We also discuss the essential issues related to the health and safety of astronauts involved in future missions, especially planned long-duration and Martian missions.

Napping on the night shift and its impact on blood pressure and heart rate variability among emergency medical services workers: study protocol for a randomized crossover trial

BACKGROUND

There is an emerging body of evidence that links exposure to shift work to cardiovascular disease (CVD). The risk of coronary events, such as myocardial infarction, is greater among night shift workers compared to day workers. There is reason to believe that repeated exposure to shift work, especially night shift work, creates alterations in normal circadian patterns of blood pressure (BP) and heart rate variability (HRV) and that these alterations contribute to increased risk of CVD. Recent data suggest that allowing shift workers to nap during night shifts may help to normalize BP and HRV patterns and, over time, reduce the risk of CVD. The risk of CVD related to shift work is elevated for emergency medical services (EMS) shift workers due in part to long-duration shifts, frequent use of night shifts, and a high prevalence of multiple jobs.

METHODS

We will use a randomized crossover trial study design with three study conditions. The targeted population is comprised of EMS clinician shift workers, and our goal enrollment is 35 total participants with an estimated 10 of the 35 enrolled not completing the study protocol or classified as lost to attrition. All three conditions will involve continuous monitoring over 72 h and will begin with a 36-h at-home period, followed by 24 total hours in the lab (including a 12-h simulated night shift), ending with 12 h at home. The key difference between the three conditions is the intra-shift nap. Condition 1 will involve a simulated 12-h night shift with total sleep deprivation. Condition 2 will involve a simulated 12-h night shift and a 30-min nap opportunity. Condition 3 will involve a simulated 12-h night shift with a 2-h nap opportunity. Our primary outcomes of interest include blunted BP dipping and reduced HRV as measured by the standard deviation of the inter-beat intervals of normal sinus beats. Non-dipping status will be defined as sleep hours BP dip of less than 10%.

DISCUSSION

Our study will address two indicators of cardiovascular health and determine if shorter or longer duration naps during night shifts have a clinically meaningful impact.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04469803 . Registered on 9 July 2020.

Mammalian circadian systems: Organization and modern life challenges

Humans and other mammalian species possess an endogenous circadian clock system that has evolved in adaptation to periodically reoccurring environmental changes and drives rhythmic biological functions, as well as behavioural outputs with an approximately 24-hour period. In mammals, body clocks are hierarchically organized, encompassing a so-called pacemaker clock in the hypothalamic suprachiasmatic nucleus (SCN), non-SCN brain and peripheral clocks, as well as cell-autonomous oscillators within virtually every cell type. A functional clock machinery on the molecular level, alignment among body clocks, as well as synchronization between endogenous circadian and exogenous environmental cycles has been shown to be crucial for our health and well-being. Yet, modern life constantly poses widespread challenges to our internal clocks, for example artificial lighting, shift work and trans-meridian travel, potentially leading to circadian disruption or misalignment and the emergence of associated diseases. For instance many of us experience a mismatch between sleep timing on work and free days (social jetlag) in our everyday lives without being aware of health consequences that may arise from such chronic circadian misalignment, Hence, this review provides an overview of the organization and molecular built-up of the mammalian circadian system, its interactions with the outside world, as well as pathologies arising from circadian disruption and misalignment.

Long-Term Effects of Very Low Dose Particle Radiation on Gene Expression in the Heart: Degenerative Disease Risks

Compared to low doses of gamma irradiation (γ-IR), high-charge-and-energy (HZE) particle IR may have different biological response thresholds in cardiac tissue at lower doses, and these effects may be IR type and dose dependent. Three- to four-month-old female CB6F1/Hsd mice were exposed once to one of four different doses of the following types of radiation: γ-IR ¹³⁷Cs (40-160 cGy, 0.662 MeV), ¹⁴Si-IR (4-32 cGy, 260 MeV/n), or ²²Ti-IR (3-26 cGy, 1 GeV/n). At 16 months post-exposure, animals were sacrificed and hearts were harvested and archived as part of the NASA Space Radiation Tissue Sharing Forum. These heart tissue samples were used in our study for RNA isolation and microarray hybridization. Functional annotation of twofold up/down differentially expressed genes (DEGs) and bioinformatics analyses revealed the following: (i) there were no clear lower IR thresholds for HZE- or γ-IR; (ii) there were 12 common DEGs across all 3 IR types; (iii) these 12 overlapping genes predicted various degrees of cardiovascular, pulmonary, and metabolic diseases, cancer, and aging; and (iv) these 12 genes revealed an exclusive non-linear DEG pattern in ¹⁴Si- and ²²Ti-IR-exposed hearts, whereas two-thirds of γ-IR-exposed hearts revealed a linear pattern of DEGs. Thus, our study may provide experimental evidence of excess relative risk (ERR) quantification of low/very low doses of full-body space-type IR-associated degenerative disease development.

A review of astronaut mental health in manned missions: Potential interventions for cognitive and mental health challenges

Space is an isolated, confined environment for humans. These conditions can have numerous effects on astronaut mental health and safety. Psychological and social issues affect space crew due to the isolation, confinement, and prolonged separation from family and friends. This area of research is particularly crucial given the space sector's plans for Martian colonies and space tourism, as well as to aid astronauts when under high stress. Therefore, this paper reviews the effects of isolation/confinement on psychological and cognitive health; impact of radiation and microgravity on cognitive health; and implications of disturbances to the circadian rhythm and sleep in space. Possible solutions to relevant mentioned cognitive and mental health challenges are also discussed.

Microgravity effects on the human brain and behavior: Dysfunction and adaptive plasticity

Emerging plans for travel to Mars and other deep space destinations make it critical for us to understand how spaceflight affects the human brain and behavior. Research over the past decade has demonstrated two co-occurring patterns of spaceflight effects on the brain and behavior: dysfunction and adaptive plasticity. Evidence indicates the spaceflight environment induces adverse effects on the brain, including intracranial fluid shifts, gray matter changes, and white matter declines. Past work also suggests that the spaceflight environment induces adaptive neural effects such as sensory reweighting and neural compensation. Here, we introduce a new conceptual framework to synthesize spaceflight effects on the brain, Spaceflight Perturbation Adaptation Coupled with Dysfunction (SPACeD). We review the literature implicating neurobehavioral dysfunction and adaptation in response to spaceflight and microgravity analogues, and we consider pre-, during-, and post-flight factors that may interact with these processes. We draw several instructive parallels with the aging literature which also suggests co-occurring neurobehavioral dysfunction and adaptive processes. We close with recommendations for future spaceflight research, including: 1) increased efforts to distinguish between dysfunctional versus adaptive effects by testing brain-behavioral correlations, and 2) greater focus on tracking recovery time courses.

Evaluation of Cardiac Circadian Rhythm Deconditioning Induced by 5-to-60 Days of Head-Down Bed Rest

Head-down tilt (HDT) bed rest elicits changes in cardiac circadian rhythms, generating possible adverse health outcomes such as increased arrhythmic risk. Our aim was to study the impact of HDT duration on the circadian rhythms of heart beat (RR) and ventricular repolarization (QTend) duration intervals from 24-h Holter ECG recordings acquired in 63 subjects during six different HDT bed rest campaigns of different duration (two 5-day, two 21-day, and two 60-day). Circadian rhythms of RR and QTend intervals series were evaluated by Cosinor analysis, resulting in a value of midline (MESOR), oscillation amplitude (OA) and acrophase (φ). In addition, the QTc (with Bazett correction) was computed, and day-time, night-time, maximum and minimum RR, QTend and QTc intervals were calculated. Statistical analysis was conducted, comparing: (1) the effects at 5 (HDT5), 21 (HDT21) and 58 (HDT58) days of HDT with baseline (PRE); (2) trends in recovery period at post-HDT epochs (R) in 5-day, 21-day, and 60-day HDT separately vs. PRE; (3) differences at R + 0 due to bed rest duration; (4) changes between the last HDT acquisition and the respective R + 0 in 5-day, 21-day, and 60-day HDT. During HDT, major changes were observed at HDT5, with increased RR and QTend intervals' MESOR, mostly related to day-time lengthening and increased minima, while the QTc shortened. Afterward, a progressive trend toward baseline values was observed with HDT progression. Additionally, the φ anticipated, and the OA was reduced during HDT, decreasing system's ability to react to incoming stimuli. Consequently, the restoration of the orthostatic position elicited the shortening of RR and QTend intervals together with QTc prolongation, notwithstanding the period spent in HDT. However, the magnitude of post-HDT changes, as well as the difference between the last HDT day and R + 0, showed a trend to increase with increasing HDT duration, and 5/7 days were not sufficient for recovering after 60-day HDT. Additionally, the φ postponed and the OA significantly increased at R + 0 compared to PRE after 5-day and 60-day HDT, possibly increasing the arrhythmic risk. These results provide evidence that continuous monitoring of astronauts' circadian rhythms, and further investigations on possible measures for counteracting the observed modifications, will be key for future missions including long periods of weightlessness and gravity transitions, for preserving astronauts' health and mission success.

Regular exercise counteracts circadian shifts in core body temperature during long-duration bed rest

With NASA's plans for the human exploration of Mars, astronauts will be exposed to mission durations much longer than current spaceflight missions on the International Space Station. These mission durations will increase the risk for circadian misalignment. Exercise has gained increasing interest as a non-pharmacological aid to entrain the circadian system. To assess the potential of exercise as a countermeasure to mitigate the risk for circadian disorders during spaceflight, we investigated the effects of long-term head-down tilt bed rest (HDBR) with and without exercise on the circadian rhythm of core body temperature. Core body temperature was recorded for 24 h using a rectal probe in sixteen healthy men (age: 30.5 ± 7.5 years (mean ± SD)) after 7 days and 49 days of HDBR. Five participants underwent HDBR only (CTR), five participants underwent HDBR and performed resistive exercises (RE), and six participants underwent HDBR and performed resistive exercises superimposed with vibrations (RVE). The exercise was scheduled three times per week. CTR showed a phase delay of 0.69 h. In contrast, both exercise groups were characterized by a phase advance (0.45 h for RE and 0.45 h for RVE; p = 0.026 for interaction between time and group). These findings suggest that resistive exercise (with or without vibration) may also serve as a countermeasure during spaceflight to mitigate circadian misalignments. The results could also be important for increasing awareness about the role of circadian disorders in long-term bedridden patients.

The individual and combined effects of spaceflight radiation and microgravity on biologic systems and functional outcomes

Both microgravity and radiation exposure in the spaceflight environment have been identified as hazards to astronaut health and performance. Substantial study has been focused on understanding the biology and risks associated with prolonged exposure to microgravity, and the hazards presented by radiation from galactic cosmic rays (GCR) and solar particle events (SPEs) outside of low earth orbit (LEO). To date, the majority of the ground-based analogues (e.g., rodent or cell culture studies) that investigate the biology of and risks associated with spaceflight hazards will focus on an individual hazard in isolation. However, astronauts will face these challenges simultaneously Combined hazard studies are necessary for understanding the risks astronauts face as they travel outside of LEO, and are also critical for countermeasure development. The focus of this review is to describe biologic and functional outcomes from ground-based analogue models for microgravity and radiation, specifically highlighting the combined effects of radiation and reduced weight-bearing from rodent ground-based tail suspension via hind limb unloading (HLU) and partial weight-bearing (PWB) models, although in vitro and spaceflight results are discussed as appropriate. The review focuses on the skeletal, ocular, central nervous system (CNS), cardiovascular, and stem cells responses.

Spaceflight and brain plasticity: Spaceflight effects on regional expression of neurotransmitter systems and neurotrophic factors encoding genes

The critical problem of space exploration is the effect of long-term space travel on brain functioning. Current information concerning the effects of actual spaceflight on the brain was obtained on rats and mice flown on five missions of Soviet/Russian biosatellites, NASA Neurolab Mission STS90, and International Space Station (ISS). The review provides converging lines of evidence that: 1) long-term spaceflight affects both principle regulators of brain neuroplasticity - neurotransmitters (5-HT and DA) and neurotrophic factors (CDNF, GDNF but not BDNF); 2) 5-HT- (5-HT_2A receptor and MAO A) and especially DA-related genes (TH, MAO A, COMT, D1 receptor, CDNF and GDNF) belong to the risk neurogenes; 3) brain response to spaceflight is region-specific. Substantia nigra, striatum and hypothalamus are highly sensitive to the long-term spaceflight: in these brain areas spaceflight decreased the expression of both DA-related and neurotrophic factors genes. Since DA system is involved in the regulation of movement and cognition the data discussed in the review could explain dysfunction of locomotion and behavior of astronauts and direct further investigations to the DA system.

Changes in performance and bio-mathematical model performance predictions during 45 days of sleep restriction in a simulated space mission

Lunar habitation and exploration of space beyond low-Earth orbit will require small crews to live in isolation and confinement while maintaining a high level of performance with limited support from mission control. Astronauts only achieve approximately 6 h of sleep per night, but few studies have linked sleep deficiency in space to performance impairment. We studied crewmembers over 45 days during a simulated space mission that included 5 h of sleep opportunity on weekdays and 8 h of sleep on weekends to characterize changes in performance on the psychomotor vigilance task (PVT) and subjective fatigue ratings. We further evaluated how well bio-mathematical models designed to predict performance changes due to sleep loss compared to objective performance. We studied 20 individuals during five missions and found that objective performance, but not subjective fatigue, declined from the beginning to the end of the mission. We found that bio-mathematical models were able to predict average changes across the mission but were less sensitive at predicting individual-level performance. Our findings suggest that sleep should be prioritized in lunar crews to minimize the potential for performance errors. Bio-mathematical models may be useful for aiding crews in schedule design but not for individual-level fitness-for-duty decisions.

Prediction of individual differences in circadian adaptation to night work among older adults: application of a mathematical model using individual sleep-wake and light exposure data

Circadian misalignment remains a distinct challenge for night shift workers. Variability in individual sleep-wake/light-dark patterns might contribute to individual differences in circadian alignment in night shift workers. In this simulation study, we compared the predicted phase shift from a mathematical model of the effect of light on the human circadian pacemaker to the observed melatonin phase shift among individuals who completed one of four interventions during simulated night shift work. Two inputs to the model were used to simulate circadian phase: sleep-wake/light-dark patterns measured from a wrist monitor (Simulation 1) and sleep-wake/light-dark patterns measured from a wrist monitor enhanced by known light levels measured at the level of the eye during simulated night shifts (Simulation 2). The estimated phase shift from the model was within 2 hours of the observed phase shift in ~80% of night shift workers for both simulations; none of the model-predicted phase shifts was more than ~3 hours from the observed phase shift. Overall, the root-mean-square error between observed and predicted phase shifts was better for Simulation 1. The light input from the wrist monitor informed by actual light level measured at the eye performed better in the sub-group exposed to bright light during their night shifts. The findings from this simulation study suggest that using a mathematical model combined with sleep-wake and light exposure data from a wrist monitor can facilitate the design of shift work schedules to enhance circadian alignment, which is expected to improve sleep, alertness, and performance.

Sleep in Isolated, Confined, and Extreme (ICE): A Review on the Different Factors Affecting Human Sleep in ICE

The recently renewed focus on the human exploration of outer space has boosted the interest toward a variety of questions regarding health of astronauts and cosmonauts. Among the others, sleep has traditionally been considered a central issue. To extend the research chances, human sleep alterations have been investigated in several analog environments, called ICEs (Isolated, Confined, and Extreme). ICEs share different features with the spaceflight itself and have been implemented in natural facilities and artificial simulations. The current paper presents a systematic review of research findings on sleep disturbances in ICEs. We looked for evidence from studies run in polar settings (mostly Antarctica) during space missions, Head-Down Bed-Rest protocols, simulations, and in a few ICE-resembling settings such as caves and submarines. Even though research has shown that sleep can be widely affected in ICEs, mostly evidencing general and non-specific changes in REM and SWS sleep, results show a very blurred picture, often with contradictory findings. The variable coexistence of the many factors characterizing the ICE environments (such as isolation and confinement, microgravity, circadian disentrainment, hypoxia, noise levels, and radiations) does not provide a clear indication of what role is played by each factor per se or in association one with each other in determining the pattern observed, and how. Most importantly, a number of methodological limitations contribute immensely to the unclear pattern of results reported in the literature. Among them, small sample sizes, small effect sizes, and large variability among experimental conditions, protocols, and measurements make it difficult to draw hints about whether sleep alterations in ICEs do exist due to the specific environmental characteristics, and which of them plays a major role. More systematic and cross-settings research is needed to address the mechanisms underlying the sleep alterations in ICE environments and possibly develop appropriate countermeasures to be used during long-term space missions.