Non-invasive monitoring of cardiac function through Ballistocardiogram: an algorithm integrating short-time Fourier transform and ensemble empirical mode decomposition.

The Ballistocardiogram (BCG) is a vibration signal that is generated by the displacement of the entire body due to the injection of blood during each heartbeat. It has been extensively utilized to monitor heart rate. The morphological features of the BCG signal serve as effective indicators for the identification of atrial fibrillation and heart failure, holding great significance for BCG signal analysis. The IJK-complex identification allows for the estimation of inter-beat intervals (IBI) and enables a more detailed analysis of BCG amplitude and interval waves. This study presents a novel algorithm for identifying the IJK-complex in BCG signals, which is an improvement over most existing algorithms that only perform IBI estimation. The proposed algorithm employs a short-time Fourier transform and summation across frequencies to initially estimate the occurrence of the J wave using peak finding, followed by Ensemble Empirical Mode Decomposition and a regional search to precisely identify the J wave. The algorithm's ability to detect the morphological features of BCG signals and estimate heart rates was validated through experiments conducted on 10 healthy subjects and 2 patients with coronary heart disease. In comparison to commonly used methods, the presented scheme ensures accurate heart rate estimation and exhibits superior capability in detecting BCG morphological features. This advancement holds significant value for future applications involving BCG signals.

Modulation of biological motion perception in humans by gravity.

The human visual perceptual system is highly sensitive to biological motion (BM) but less sensitive to its inverted counterpart. This perceptual inversion effect may stem from our selective sensitivity to gravity-constrained life motion signals and confer an adaptive advantage to creatures living on Earth. However, to what extent and how such selective sensitivity is shaped by the Earth's gravitational field is heretofore unexplored. Taking advantage of a spaceflight experiment and its ground-based analog via 6° head-down tilt bed rest (HDTBR), we show that prolonged microgravity/HDTBR reduces the inversion effect in BM perception. No such change occurs for face perception, highlighting the particular role of gravity in regulating kinematic motion analysis. Moreover, the reduced BM inversion effect is associated with attenuated orientation-dependent neural responses to BM rather than general motion cues and correlated with strengthened functional connectivity between cortical regions dedicated to visual BM processing (i.e., pSTS) and vestibular gravity estimation (i.e., insula). These findings suggest that the neural computation of gravity may act as an embodied constraint, presumably implemented through visuo-vestibular interaction, to sustain the human brain's selective tuning to life motion signals.

Performance, Workload, and Situation Awareness in Manual and Automation-Aided Rendezvous and Docking.

BACKGROUND: Manual rendezvous and docking (RVD) is challenging for the astronauts, and automation is used to aid this operation. However, the automation mode in the final approaching stance of RVD is quite different. This paper is aimed at investigating the effect of automation on performance, workload and situation awareness (SA) among novice and expert operators in RVD.METHODS: A two-factor mixed experimental design was adopted. There were 15 novices and 12 experts who participated in the experiment. All subjects were required to finish six tasks of two automation levels: manual RVD and automation-aided RVD. The Performance was assessed by docking result and control process. Workload and SA were measured by NASA Task Load Index and Situation Awareness Rating Techniques (SART). Repeat measures ANOVA and the simple effect test were used to analyze the effect of automation, skill level, and the interaction between them on performance, workload, and SA of operators.RESULTS: Novices exhibited performances inferior to experts, but the skills gap was attenuated as automation was introduced. Moreover, automation can enhance performance, reduce workload, and enhance SA for novices, but potentially deteriorate task performance and SA for the experienced. Mediation analysis results indicated automation was a significant predictor of workload and SA, b = -0.576 and b = 0.503, and workload and SA were significant predictors of docking result, b = -0.590 and b = 0.348.CONCLUSION: Automation can be detrimental to various elements of the functioning of highly experienced operators. Moreover, automation affects docking result by affecting workload and SA.Du X, Niu J, Zhang Y, Wang M, Wang D, Wu B, Cai J, Huang W. Performance, workload, and situation awareness in manual and automation-aided rendezvous and docking. Aerosp Med Hum Perform. 2019; 90(5):447-455.

The influence of spatial ability and experience on performance during spaceship rendezvous and docking.

Manual rendezvous and docking (manual RVD) is a challenging space task for astronauts. Previous research showed a correlation between spatial ability and manual RVD skills among participants at early stages of training, but paid less attention to experts. Therefore, this study tried to explore the role of spatial ability in manual RVD skills in two groups of trainees, one relatively inexperienced and the other experienced operators. Additionally, mental rotation has been proven essential in RVD and was tested in this study among 27 male participants, 15 novices, and 12 experts. The participants performed manual RVD tasks in a high fidelity simulator. Results showed that experience moderated the relation between mental rotation ability and manual RVD performance. On one hand, novices with high mental rotation ability tended to perform that RVD task more successfully; on the other hand, experts with high mental rotation ability showed not only no performance advantage in the final stage of the RVD task, but had certain disadvantages in their earlier processes. Both theoretical and practical implications were discussed.

Comparison of heart rate variability and heart rate between individuals with different emotional stability in two situations.

OBJECTIVE: To compare heart rate variability (HRV) and heart rate (HR) between individuals with different emotional stabilities in two situations and to discuss the relationship between situation, emotional stability and HRV. METHOD: Ninety-six healthy male flying students were assessed after 60 h flying exercises by senior pilots using Criterion Assessment Scale of Emotional Stability of Flying Cadets (CASESFC) compiled by our department. They were divided into groups of high emotional stability and low stability. ECG were recorded in situations of Sternberg Dual Task and Flying and HRV components and HR were analyzed and compared. RESULT: When subjects were exposed to Sternberg dual task situation, individuals with high emotional stability had lower LFnorm (P<0.05), HFnorm (P<0.05), LF/HF ratio and HR (P<0.05) than those with low emotional stability. When it comes to flying situation, individuals with high emotional stability had higher LFnorm and HFnorm, but LF/HF ratio and HR (P<0.05) were still lower than those with low emotional stability. CONCLUSION: We found that there is a tendency which implies the situational separation of fluctuation of autonomic nervous system related to emotional stability. It suggests that the ability of an individual to adjust to outer environment depends not only on personality, temperament and cognitive module, but also on a physiological basis.

[Models of confirmatory factor analysis of the emotional stability criteria of flying students].

OBJECTIVE: To established models of confirmatory factor analysis of the emotional stability criteria of flying students, and to provide an available criteria tool for evaluating the emotional stability. METHOD: "Criterion Assessment Scale of Emotional Stability of Flying Cadets" (ACSEFC) including 9 items were compiled first by interviewing with skillful pilots or flying instructors, and then the emotional stability of 153 flying students was evaluated by these pilots or instructors. RESULT: There were high level (P<0.05) of correlation coefficients between 8 items except for item 1; three-factor design appears to be the best choice for the nine items by exploratory factor analysis; model 4 appears to have the best effect by confirmatory factor analysis. CONCLUSION: The evaluation of emotional stability of flying students can be divided into 3 parts: general manifest emotion, tense before flying and flying emotion stability.

[Effects of exercise training during 21 d -6 degrees head down bed rest on dynamic posture equilibrium and motor coordination].

OBJECTIVE: To study the effects of 21 d -6 degrees head down bed rest (HDBR) with exercise training on dynamic posture equilibrium and motor coordination. METHOD: Ten healthy young men were randomly divided into HDBR control groups and HDBR exercise groups, with 5 in each group. The subjects in the exercise group performed exercise with a bicycle ergometer in the supine position 1 h/d during bed rest. Dynamic posture equilibrium as well as isokinetic concentric muscular strength were determined before and after 21 d HD-BR. RESULT: After HDBR, average dynamic proprioception score and dynamic motor coordination decreased significantly, relative peak torque (peak torque /body weights PT/BW) also decreased significantly and accompanied with increase of the peak torque ratio between hamstrings and quadriceps (H/Q) in HDBR control groups. Average dynamic proprioception score and dynamic motor coordination in the HDBR exercise groups remained above the HDBR control groups, but the H/Q ratio showed no significant change. CONCLUSION: The results showed that exercise training during 21 d -6 degrees head-down tilt bed-rest do have beneficial effects on retaining the dynamic posture equilibrium and dynamic motor coordination of the subjects after bed rest.

[Study on relationship between emotional stability in flight and nerve system excitability].

OBJECTIVE: To study the related factors of emotional stability in flight. METHOD: Based on the operable definition of emotional stability in flight and the related literature review, 63 experienced pilots and flight coaches were investigated and the other-rating questionnaire of emotional stability in flight was established. To test the senior nerve system, Uchida Kraeplin (UK) test was administrated on 153 19-21 years old male student pilots of the second grade in the department of flight technique in China Civil Aviation College, who were selected through 13 h flight, 35 h solo flight, and acted as the standardization group. In the end, the correlation was explored between the testing results and their emotional behavioral characteristics in flight. RESULT: Significant positive correlation was found between emotional feature indexes of emotional stability in flight and excitability in UK test. CONCLUSION: The excitability in UK test are good predictors for emotional stability in flight.

[Preventive effects of exercise training on bone loss during 21 d -6 degrees head down bed-rest].

OBJECTIVE: To observe the protective effects of exercise training during 21 d -6 degrees head down bed rest (HDBR) on bone loss. METHOD: Ten healthy young men were randomly divided into HDBR group and HD-BR exercise group, with 5 in each group. Both groups were exposed to -6 degrees head down bed rest for 21 d. The subjects in the exercise group performed exercise with a bicycle ergometer in supine position 1 h/d during bed rest. Femur bone mineral density (BMD), serum bone gla protein (BGP) as well as hydroxyproline/creatinine (HOP/Cr) were determined before and during 20 d HDBR. RESULT: As compared with the before HDBR values, average femur BMD decreased by 5.8% and 0.9% for HDBR group and HDBR and exercise group respectively. HOP/Cr significantly increased in the HDBR group and was significantly higher than the HDBR exercise group. BGP decreased in both groups with no significant difference. CONCLUSION: Exercise during 21 d -6 degrees HDBR is beneficial in preventing bone loss.

[Application of lower body negative pressure (LBNP) in aerospace medicine].

Effects of LBNP is similar to that produced by gravitational force, especially as a stress factor on the cardiovascular system as has been concerned in the area of aerospace medicine. This paper described experimental equipment, methods and physiological effects of LBNP, especially its application in the area of aerospace medicine. Several aspects for future research were put forward.

[Effects of +Gx load on energy metabolism of brain tissue in rats].

Objective. To observe the changes of energy metabolism of brain tissue in rats under +Gx loads, and to explore its possible role in changes of brain function and work efficiency induced by +Gx stress. Method. Forty-five male Wistar rats were randomly divided into control, +5 Gx, +10 Gx, +15 Gx and +20 Gx group. Each group was exposed to the corresponding G value for 3 min. After that, cortical adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and lactic acid (LA) content, lactate dehydrogenase (LDH) activity were measured. Result. Compared with the control group, the cortical (LA) content increased significantly after +5 Gx, +10 Gx, +15 Gx and +20 Gx exposure (P<0.01). Cortical ADP content and ratio of ADP/AMP and AMP/ATP increased significantly after +10 Gx, +15 Gx and +20 Gx exposure (P<0.01), whereas ATP content, energy charge and LDH activity decreased significantly (P<0.05 or 0.01). Cortical AMP content increased significantly after +15 Gx and +20 Gx exposure (P<0.05 and 0.01). Conclusion. It is suggested that +Gx load can result in obvious depression of brain energy metabolism, which could be an important reason for the change of brain function and work efficiency induced by +Gx stress.