Sufficient sleep duration and good sleep quality are crucial to ensure normal physical and mental health, cognition and work performance for the common people, as well as astronauts. On-orbit sleep problem is very common among astronauts and has potential detrimental influences on the health of crewmembers and the safety of flight missions. Sleep in space is becoming a new medical research frontier. In this review we summarized on-orbit sleep problems of astronauts and six kinds of causes, and we presented the effects of lack of sleep on performance as well as mental and physical health, then we proposed seven kinds of countermeasures for sleep disturbance in spaceflight, including pharmacologic interventions, light treatment, crew selection and training, Traditional Chinese Medicine and so on. Furthermore, we discussed and oriented the prospect of researches on sleep in space.

Fasting shows great potential in preventing chronic diseases and has to be surmounted under some extraordinary circumstances. This study aimed to investigate the safety, time effects of metabolic homeostasis and health indexes during prolonged fasting. Thirteen participants were recruited to conduct a 10-day complete fasting (CF) in a controlled health research building under medical supervision including 3-day Baseline (BL), 10-day CF, 4-day calorie restriction (CR) and 5-day full recovery (FR). Body healthy status was assessed by surveying pulse, blood pressure, body weight (BW), blood glucose and ketones, body composition and nutritional and biochemistry indexes at different times. BW declined about 7.28 kg (−9.8%) after 10-day CF, accompanied by increased pulse and decreased systolic blood pressure, but there were no changes to the myocardial enzymogram. Body composition analysis showed fat mass was constantly lost, but lean mass could recover after CR. The energy substrate switch from glucose to ketone occurred and formed a stable dynamic balance between 3–6 days of CF. The lipid metabolism presented increased total cholesterol, LDL-C, ApoA1 and almost no changes to TG and HDL-C. Prolonged CF did not influence liver function, but induced a slight decrease of kidney function. The interesting results came from the marked increase of lipid-soluble vitamins and a significant decrease of sodium and chlorine. Adults could well tol-erate a 10-day CF. A new metabolic homeostasis was achieved. No vitamins but NaCl supplement should be considered. These findings provide evidence to design a new fasting strategy for clinical practice.

Objectives. The present study aimed to investigate the effects of guided imagery training on heart rate variability in individuals while performing spaceflight emergency tasks.Materials and Methods. Twenty-one student subjects were recruited for the experiment and randomly divided into two groups: imagery group (n=11) and control group (n=10). The imagery group received instructor-guided imagery (session 1) and self-guided imagery training (session 2) consecutively, while the control group only received conventional training. Electrocardiograms of the subjects were recorded during their performance of nine spaceflight emergency tasks after imagery training.Results. In both of the sessions, the root mean square of successive differences (RMSSD), the standard deviation of all normal NN (SDNN), the proportion of NN50 divided by the total number of NNs (PNN50), the very low frequency (VLF), the low frequency (LF), the high frequency (HF), and the total power (TP) in the imagery group were significantly higher than those in the control group. Moreover, LF/HF of the subjects after instructor-guided imagery training was lower than that after self-guided imagery training.Conclusions. Guided imagery was an effective regulator for HRV indices and could be a potential stress countermeasure in performing spaceflight tasks.

With the continuing progress in space exploration, a new and perplexing condition related to spaceflight ocular syndrome has emerged in the past four decades. National Aeronautics and Space Administration (NASA) has named this condition “spaceflight-associated neuro-ocular syndrome” (SANS). This article gives an overview of the current research about SANS and traditional Chinese medicine (TCM) by analyzing the existing publications on PubMed and CNKI and reports from NASA about SANS, summarizing the potential pathogenesis of SANS and physical interventions for treating SANS, and discussing the feasibility of treating SANS with TCM. Due to the unique characteristics of the space environment, it is infeasible to conduct large-scale human studies of SANS. SANS may be the result of the interaction of multiple factors, including inflammation and fluid displacement in the optic nerve sheath and cerebrospinal fluid. We should pay attention to SANS. Visual function is not only related to the health of astronauts but also closely related to space operations. TCM has antioxidative stress and antiapoptotic effects and is widely used for optic nerve diseases. TCM has great potential to prevent SANS.

During a spaceflight, astronauts need to live in a spacecraft on orbit for a long time, and the relationship between humans and microorganisms in the closed environment of space is not the same as on the ground. The dynamic study of microorganisms in confined space shows that with the extension of the isolation time, harmful bacteria gradually accumulate. Monitoring and controlling microbial pollution in a confined environment system are very important for crew health and the sustainable operation of a space life support system. Culture‐based assays have been used traditionally to assess the microbial loads in a spacecraft, and uncultured‐based techniques are already under way according to the NASA global exploration roadmap. High‐throughput sequencing technology has been used generally to study the communities of the environment and human on the ground and shows its broad prospects applied onboard. We here review the recent application of high‐throughput sequencing on space microbiology and analyze its feasibility and potential as an on‐orbit detection technology.

Wu B, Xue Y, Wu P, Gu Z, Wang Y, Jing X. Physiological responses of astronaut candidates to simulated +G_x orbital emergency re-entry. Aviat Space Environ Med 2012; 83:758–63. Introduction: We investigated astronaut candidates’ physiological and pathological responses to +G_x exposure during simulated emergency return from a running orbit to advance astronaut +G_x tolerance training and medical support in manned spaceflight. Methods: There were 13 male astronaut candidates who were exposed to a simulated high +G_x acceleration profile in a spacecraft during an emergency return lasting for 230 s. The peak value was 8.5 G. Subjective feelings and symptoms, cardiovascular and respiratory responses, and changes in urine component before, during, and after +G_x exposure were investigated. Results: Under high +G_x exposure, 15.4% of subjects exhibited arrhythmia. Heart rate (HR) increased significantly and four different types of HR response curves were distinguished. The ratio of QT to RR interval on the electrocardiograms was significantly increased. Arterial oxygen saturation (S_ao₂) declined with increasing G value and then returned gradually. S_ao₂ reached a minimum (87.7%) at 3 G during the decline phase of the +G_x curve. Respiratory rate increased significantly with increasing G value, while the amplitude and area of the respiratory waves were significantly reduced. The overshoot appeared immediately after +G_x exposure. A few subjects suffered from slight injuries, including positive urine protein (1/13), positive urinary occult blood (1/13), and a large area of petechiae on the back (1/13). Conclusions: Astronaut candidates have relatively good tolerance to the +G_x profile during a simulation of spacecraft emergent ballistic re-entry. However, a few subjects exhibited adverse physiological responses and slight reversible pathological injuries.