Numerical analysis of the hemodynamics of rat aorta based on magnetic resonance imaging and fluid-structure interaction.

Murine models have been widely used to investigate the mechanobiology of aortic atherosclerosis and dissections, which develop preferably at different anatomic locations of aorta. Based MRI and finite element analysis with fluid-structure interaction, we numerically investigated factors that may affect the blood flow and structural mechanics of rat aorta. The results indicated that aortic root motion greatly increases time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), displacement of the aorta, and enhances helical flow pattern but has limited influence on effective stress, which is highly modulated by blood pressure. Moreover, the influence of the motion component on these indicators is different with axial motion more obvious than planar motion. Surrounding fixation of the intercostal arteries and the branch vessels on aortic arch would reduce the influence of aortic root motion. The compliance of the aorta has different influences at different regions, leading to decrease in TAWSS and helical flow, increase in OSI, RRT at the aortic arch, but has reversed effects on the branch vessels. When compared with the steady flow, the pulsatile blood flow would obviously increase the WSS, the displacement, and the effective stress in most regions. In conclusion, to accurately quantify the blood flow and structural mechanics of rat aorta, the motion of the aortic root, the compliance of aortic wall, and the pulsation of blood flow should be considered. However, when only focusing on the effective stress in rat aorta, the motion of the aortic root may be neglected.

Effects of vibration training in reducing risk of slip-related falls among young adults with obesity.

This study examined the effects of controlled whole-body vibration training on reducing risk of slip-related falls in people with obesity. Twenty-three young adults with obesity were randomly assigned into either the vibration or placebo group. The vibration and placebo groups respectively received 6-week vibration and placebo training on a side-alternating vibration platform. Before and after the training, the isometric knee extensors strength capacity was measured for the two groups. Both groups were also exposed to a standardized slip induced by a treadmill during gait prior to and following the training. Dynamic stability and fall incidences responding to the slip were also assessed. The results indicated that vibration training significantly increased the muscle strength and improved dynamic stability control at recovery touchdown after the slip occurrence. The improved dynamic stability could be resulted from the enhanced trunk segment movement control, which may be attributable to the strength increment caused by the vibration training. The decline of the fall rates from the pre-training slip to the post-training one was greater among the vibration group than the placebo group (45% vs. 25%). Vibration-based training could be a promising alternative or additional modality to active exercise-based fall prevention programs for people with obesity.

Strength or power, which is more important to prevent slip-related falls?

Falls are a serious health and medical concern facing older adults worldwide. Both muscle strength and power have been related to falls among older adults. The primary purpose of this study was to identify which one of these two muscular performances is more important in preventing a slip-related fall. Twenty-six healthy young adults participated in this study. Their muscle strength (torque) and power capacities were assessed at the right knee under maximum voluntary isometric (flexion and extension) and isokinetic (concentric extension and flexion at three different contraction speeds: 60 deg/s, 120 deg/s, and 180 deg/s) contractions, respectively. They were then subjected to an identical and unannounced slip during gait on a treadmill under the protection of a safety harness after walking regularly for five times on the treadmill. Accuracy of predicting slip outcome (fall vs. recovery) was examined for each muscle performance measurement using logistic regression. Results showed that overall the joint power capacity measurements predicted the slip outcome among these subjects with higher accuracy than did the joint torque capacity measurements. Such results suggested that muscle power could be more closely related to a fall initiated by a slip during gait. The findings from the present study could provide guidance to identify individuals at increased risk of falling using the joint power capacity measurement and to design effective fall prevention training paradigms aiming at maximizing muscle power among older adults and others with physical disabilities.

Low-arousal speech noise improves performance in N-back task: an ERP study.

The relationship between noise and human performance is a crucial topic in ergonomic research. However, the brain dynamics of the emotional arousal effects of background noises are still unclear. The current study employed meaningless speech noises in the n-back working memory task to explore the changes of event-related potentials (ERPs) elicited by the noises with low arousal level vs. high arousal level. We found that the memory performance in low arousal condition were improved compared with the silent and the high arousal conditions; participants responded more quickly and had larger P2 and P3 amplitudes in low arousal condition while the performance and ERP components showed no significant difference between high arousal and silent conditions. These findings suggested that the emotional arousal dimension of background noises had a significant influence on human working memory performance, and that this effect was independent of the acoustic characteristics of noises (e.g., intensity) and the meaning of speech materials. The current findings improve our understanding of background noise effects on human performance and lay the ground for the investigation of patients with attention deficits.

[An experimental study of effects of active-heating-system for extravehicular spacesuit gloves on working performance].

OBJECTIVE: To observe the effects of active heating system for spacesuit gloves on extravehicular working performance. METHOD: After analyzing the factors with gloves influence on the working performance, the effects of active heating system for gloves were studied experimentally with aspects to fatigue, hand strength, dexterity and tactile sensing. RESULT: 1) Heating-system had not influence to grip; 2) Heating-system had 17% influence to fatigue except specific person; 3) Nut assembly and nipping pin showed that heating-system had little influence to dexterity; 4) Apperceiving shape of object and two-point distance showed heating-system had little influence to tactility. CONCLUSION: The active heating method is rational and has little influence on working performance.