Development and validation of rear impact computer simulation model of an adult manual transit wheelchair with a seated occupant

It has been shown that ANSI WC19 transit wheelchairs that are crashworthy in frontal impact exhibit catastrophic failures in rear impact and may not be able to provide stable seating support and thus occupant protection for the wheelchair occupant. Thus far only limited sled test and computer simulation data have been available to study rear impact wheelchair safety. Computer modeling can be used as an economic and comprehensive tool to gain critical knowledge regarding wheelchair integrity and occupant safety. This study describes the development and validation of a computer model simulating an adult wheelchair-seated occupant subjected to a rear impact event. The model was developed in MADYMO? and validated rigorously using the results of three similar sled tests conducted to specifications provided in the draft ISO/TC 173 standard. Outcomes from the model can provide critical wheelchair loading information to wheelchair and tiedown manufacturers, resulting in safer wheelchair designs for rear impact conditions.     

The relationship between lower neck shear force and facet joint kinematics during automotive rear impacts

A primary goal of biomechanical safety research is the definition of localized injury thresholds in terms of quantities that are repeatable and easily measureable during experimentation. Recent biomechanical experimentation using human cadavers has highlighted the role of lower cervical facet joints in the injury mechanism resulting from low-speed automotive rear impacts. The present study was conducted to correlate lower neck forces and moments with facet joint motions during simulated rear impacts in an effort to define facet joint injury tolerance thresholds that can be used to assess automobile safety. Four male and four female intact head-neck complexes were obtained from cadaveric specimens and subjected to simulated automotive rear impacts using a pendulum-minisled device. Cervical spine segmental angulations and localized facet joint kinematics were correlated to shear and axial forces, and bending moments at the cervico-thoracic junction using linear regression. R(2) coefficients indicated that spinal kinematics correlated well with lower neck shear force and bending moment. Correlation slope was steeper in female specimens, indicating greater facet joint motions for a given loading magnitude. This study demonstrated that lower neck loads can be used to predict lower cervical facet joint kinematics during automotive rear impacts. Higher correlation slope in female specimens corresponds to higher injury susceptibility in that population. Although lower neck shear force and bending moment demonstrated adequate correlation with lower cervical facet joint motions, shear force is likely the better predictor due to similarity in the timing of peak magnitudes with regard to maximum facet joint motions.     

Cortisol and testosterone concentrations in wheelchair athletes during submaximal wheelchair ergometry

It is yet unknown how upper body exercise combined with high ambient temperatures affects plasma testosterone and cortisol concentrations and furthermore, how these hormones respond to exercise in people suffering spinal cord injuries. The purpose of this study was to characterize plasma testosterone and cortisol responses to upper body exercise in wheelchair athletes (WA) compared to able-bodied individuals (AB) at two ambient temperatures. Four WA [mean age 36 (SEM 13) years, mean body mass 66.9 (SEM 11.8) kg, injury level T₇–T₁₁], matched with five AB [mean age 33.4 (SEM 8.9) years, mean body mass 72.5 (SEM 13.1) kg] exercised (cross-over design) for 20 min on a wheelchair ergometer (0.03 kg resistance · kg⁻¹ body mass) at 25 °C and 32 °C. Blood samples were obtained before (PRE), at min 10 (MID), and min 20 (END) of exercise. No differences were found between results obtained at 25 °C and 32 °C for any physiological variable studied and therefore these data were combined. Pre-exercise testosterone concentration was lower (P < 0.05) in WA [18.3 (SEM 0.9) nmol · l⁻¹] compared to AB [21.9 (SEM 3.6) nmol · l⁻¹], and increased PRE to END only in WA. Cortisol concentrations were similar between groups before and during exercise, despite higher rectal temperatures in WA compared to AB, at MID [37.21 (SEM  0.14) and 37.02 (SEM  0.08)°C, respectively] and END [37.36 (SEM 0.16) and 37.19 (SEM 0.10)°C, respectively]. Plasma norepinephrine responses were similar between groups. In conclusion, there were no differences in plasma cortisol concentrations, which may have been due to the low relative exercise intensities employed. The greater exercise response in WA for plasma testosterone should be confirmed on a larger population. It could have been the result of the lower plasma testosterone concentrations at rest in our group. Accepted: 4 September 2000     

Mathematical model for investigating combined seatback—head restraint performance during rear-end impact

A mathematical model of the seated driver subjected to a rear-end impact is developed using a lumped parameter model which,inter alia, allows for the investigation of the effect of an elastic—perfectly plastic head restraint device on the overall motion of the head and torso. The most satisfactory seatback-head restraint combination is found to be a seatback having a high rotational stiffness with a viscous damping coefficient of near ‘critical’ value combined with an energy absorbing head restraint having e plastic collapse load of approximately 890 N. The model confirms recent results which indicate that tensing of neck musculature prior to impact reduces injury potential.     

Modeling of occupant dynamics during automobile rear-end impacts

Procedures for studying the dynamic response of the occupant within a rear-end impacted vehicle are presented. Most of the researches in the impact analysis were performed by experimental approach and this costs a lot of time and money. Especially, the repeatability is very hard to produce in a destructive condition. Most of all, the analytic parameters can be investigated are limited by the experimental approach. By using numerical techniques, this research employs Kane's equation and Huston's method to develop a simulated system with visual graphic output to observe the rear-end impact response. According to the simulated results, at a constant seatback angle the maximum acceleration values of head and chest increased with the increasing of impact velocity. Furthermore, at a constant impact velocity the relative rotation angle of a passenger's head to chest decreased with the increasing of initial seatback angle.     

Concept of a platform-based impact isolation system for protection of wheelchair occupants from injuries in vehicle crashes

To improve the protection of a wheelchair-seated person with disabilities traveling in a vehicle from injuries in a crash, it is proposed to attach the wheelchair to a movable platform separated from the vehicle body by means of a shock isolator. The control of the platform is designed to reduce the occupant's injury risk, as compared with the case of the attachment of the wheelchair directly to the vehicle. The isolator design is based on the minimization of the force transmitted to the wheelchair occupant, provided that the space allowed for the platform to move relative to the vehicle is constrained. The possibility of pre-acting control, when the isolator is engaged for a time prior to the crash, is discussed. Passive tiedown and restraint systems are studied, although it is recognized that active systems could provide even lower injury risks. A multibody model of the platform-based occupied wheelchair is utilized for full-scale simulation of the response of the system to a crash pulse. The simulation shows a noticeable reduction in the injury risk due to the platform and an even greater reduction of injury with pre-acting control.     

Effects of user's actions on rolling resistance and wheelchair stability during handrim wheelchair propulsion in the field

Currently, rolling resistance and wheelchair stability during manual wheelchair propulsion can be assessed from the loads applied on the front and rear wheels, which are determined in a static condition. However, a user's actions on the wheelchair would change these loads during locomotion, which should affect both the rolling resistance and wheelchair stability. The goal of this study was to verify these assumptions and assess how much the rolling resistance and wheelchair stability are affected by the user's actions during propulsion. For that purpose, a mechanical model was developed using measurements of an instrumented wheelchair equipped with several six-component dynamometers. Experiments were performed by three subjects propelling the instrumented wheelchair over flat ground. The results showed variations over wide ranges of the fore-aft distribution of the total load, rolling resistance, wheelchair stability, wheelchair velocity and mechanical power dissipated by the rolling resistance during the propulsion cycle. In addition, the time courses of all these variables differed with the subject. Finally, this study demonstrated the possibility of assessing intra-cycle values of both rolling resistance and wheelchair stability during manual wheelchair displacements in the field, which provides a technical step towards evaluating a wheelchair user in his daily environment.     

两种疲劳方案对落地时下肢运动学和冲击力时频特征的影响

目的比较两种疲劳方案对人体落地动作下肢关节运动学及冲击力时/频域特征的影响。方法选取15名优秀跑、跳类专项男性运动员,利用Vicon运动捕捉系统和Kistler三维测力台比较两种疲劳方案(恒速跑、折返跑+垂直纵跳)前后落地时矢、额状面运动学和地面反作用力(ground reaction force,GRF)时/频域特征。结果(1)两种疲劳方案均会造成髋、膝关节在矢状面上的角度减小、屈曲活动度增加,且采用跑+跳方案时踝关节屈曲活动度、膝关节最大屈曲角速度增加(P0.05),髋关节外展活动度以及髋、膝关节最大外展角速度增加(P0.05);(2)两种疲劳方案前后,冲击力时域特征均无显著差异;采用跑和跑+跳方案,分别在3.51、8.20 Hz及1.17、3.51、7.03 Hz下表现出GRF频谱振幅减小(P0.05)。结论两种疲劳方案均会导致下肢在受到落地冲击时更多采用屈曲着地方式,但跑+跳方案表现更明显且干预时间更短,从实验方法学角度更具优势。研究结果可为研究疲劳后的力特征提供进一步参考。     

Prediction of peak oxygen uptake from differentiated ratings of perceived exertion during wheelchair propulsion in trained wheelchair sportspersons

Purpose

To assess the validity of predicting peak oxygen uptake ( $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ ) from differentiated ratings of perceived exertion (RPE) obtained during submaximal wheelchair propulsion.

Methods

Three subgroups of elite male wheelchair athletes [nine tetraplegics (TETRA), nine paraplegics (PARA), eight athletes without spinal cord injury (NON-SCI)] performed an incremental speed exercise test followed by graded exercise to exhaustion ( $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ test). Oxygen uptake ( $ {\dot{\text{V}}}{\text{O}}_2$ ), heart rate (HR) and differentiated RPE (Central RPE_C, Peripheral RPE_P and Overall RPE_O) were obtained for each stage. The regression lines for the perceptual ranges 9–15 on the Borg 6–20 scale ratings were performed to predict $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ .

Results

There were no significant within-group mean differences between measured $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ (mean 1.50 ± 0.39, 2.74 ± 0.48, 3.75 ± 0.33 L min^?1 for TETRA, PARA and NON-SCI, respectively) and predicted $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ determined using HR or differentiated RPEs for any group (P > 0.05). However, the coefficients of variation (CV %) between measured and predicted $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ using HR showed high variability for all groups (14.3, 15.9 and 9.7 %, respectively). The typical error ranged from 0.14 to 0.68 L min^?1 and the CV % between measured and predicted $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ using differentiated RPE was ≤11.1 % for TETRA, ≤7.5 % for PARA and ≤20.2 % for NON-SCI.

Conclusions

Results suggest that differentiated RPE may be used cautiously for TETRA and PARA athletes when predicting $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ across the perceptual range of 9–15. However, predicting $ {\dot{\text{V}}}{\text{O}}_{{\text{2peak}}}$ is not recommended for the NON-SCI athletes due to the large CV %s (16.8, 20.2 and 18.0 %; RPE_C, RPE_P and RPE_O, respectively).     

Patellar resurfacing has minimal impact on in vitro tibiofemoral kinematics during deep knee flexion in total knee arthroplasty

BackgroundWhile patellar resurfacing can affect patellofemoral kinematics, the effect on tibiofemoral kinematics is unknown. We hypothesized that patellar resurfacing would affect tibiofemoral kinematics during deep knee flexion due to biomechanical alteration of the extensor mechanism.MethodsWe performed cruciate-retaining TKA in fresh-frozen human cadaveric knees (N = 5) and recorded fluoroscopic kinematics during deep knee flexion before and after the patellar resurfacing. To simulate deep knee flexion, cadaver knees were tested on a dynamic, quadriceps-driven, closed-kinetic chain simulator based on the Oxford knee rig design under loads equivalent to stair climbing. To measure knee kinematics, a 2-dimensional to 3-dimensional fluoroscopic registration technique was used. Component rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were calculated over the range of flexion.ResultsThere were no significant differences in femoral component external rotation (before patellar resurfacing: 6.6 ± 2.3°, after patellar resurfacing: 7.2 ± 1.8°, p = 0.36), and less than 1° difference in femorotibial varus-valgus angle between patellar resurfacing and non-resurfacing (p = 0.01). For both conditions, the medial and lateral femorotibial contact points moved posteriorly from 0° to 30° of flexion, but not beyond 30° of flexion. At 10° of flexion, after patellar resurfacing, the medial contact point was more anteriorly located than before patellar resurfacing.ConclusionDespite the potential for alteration of the knee extensor biomechanics, patellar resurfacing had minimal effect on tibiofemoral kinematics. Patellar resurfacing, if performed adequately, is unlikely to affect postoperative knee function.     

基于Matlab环境的脑控轮椅搭建与实验验证

目的基于脑电(electroencephalography,EEG)的脑控轮椅(brain-controlled wheelchair,BCW)能够为无法通过四肢操控轮椅运动的严重肢体残疾或运动障碍患者提供辅助,满足日常移动或出行需要。本文以兼顾系统性价比和准确率为研究目的,采用便携脑电放大器,搭建一个基于Matlab环境的BCW系统,并验证系统的可行性和实用性。方法首先搭建一个基于稳态视觉诱发电位(steadystate visual evoked potential,SSVEP)的BCW系统,系统主要包括脑电刺激、采集与处理,以及轮椅控制两大部分,用户无需长期训练即可通过脑电控制轮椅的运动状态。然后招募3名健康受试者进行系统分类准确率验证实验和预设路径控制验证实验。其中,分类准确率验证实验要求受试者按照语音提示指令,注视对应刺激闪烁块以得到分类结果;预设路径控制验证实验要求受试者完成3个轮椅既定路线控制任务。实验后填写问卷调查衡量本系统的控制难度、受试者舒适度和疲劳程度。结果比较提示指令与分类结果得到系统分类准确率为97%±1%。路径控制实验中受试者均能控制轮椅按照预设路径运动到目的地,且获得用时、实际路径长度、命令个数、时间优化率、路径优化率等指标。结论本文搭建的基于Matlab环境的SSVEP-BCW系统分类准确率较高,控制效果和控制舒适度较好,具有一定的实用性。     

Non-uniform temporal scaling of hand and finger kinematics during typing

We examined the manner in which the keystroke kinematics of the hand and the fingers varied with the mean rate of typing by trained typists. We used words and phrases in which only one letter was typed with the right hand and all of the remaining letters were typed using the left hand. We varied the typing rate over a threefold range (intervals between keypresses ranging from 150 ms to 500 ms) with the aid of a metronome. The results from four subjects, and three letters (n, u, and o) were analyzed. We did not find a simple scaling that could account for variations in the velocity profiles with typing rate. For some subjects and some letters, the velocities were independent of typing rate. In other instances, the kinematics did depend on typing rate, but to a much greater extent prior to the time of keypress than afterward. Sometimes the velocity profiles of all of the fingers and of the hand changed in a similar manner as the interval between keypresses was varied. In other instances only the focal movement of the hand and the finger used to press the key depended on the interval, whereas the motions of the other fingers did not. We suggest that the consistencies in the velocity profiles which we observed may simplify the problem of arranging a temporally ordered sequence of goal-directed movements.     

Integrated pressure-force-kinematics measuring system for the characterisation of plantar foot loading during locomotion

Plantar pressure, ground reaction force and body-segment kinematics measurements are largely used in gait analysis to characterise normal and abnormal function of the human foot. The combination of all these data together provides a more exhaustive, detailed and accurate view of foot loading during activities than traditional measurement systems alone do. A prototype system is presented that integrates a pressure platform, a force platform and a 3D anatomical tracking system to acquire combined information about foot function and loading. A stereophotogrammetric system and an anatomically based protocol for foot segment kinematics is included in a previously devised piezo-dynamometric system that combines pressure and force measurements. Experimental validation tests are carried out to check for both spatial and time synchronisation. Misalignment of the three systems is found to be within 6.0, 5.0 and 1.5mm for the stereophotogrammetric system, force platform and pressure platform, respectively. The combination of position and pressure data allows for a more accurate selection of plantar foot subareas on the footprint. Measurements are also taken on five healthy volunteers during level walking to verify the feasibility of the overall experimental protocol. Four main subareas are defined and identified, and the relevant vertical and shear force data are computed. The integrated system is effective when there is a need for loading measurements in specific plantar foot subareas. This is attractive both in clinical assessment and in biomechanics research.     

Response of human and anthropometric model skulls to impact loading

Experimental strain/time results are presented for unprotected and protected human and anthropometric model skulls under impact loading. Using a hockey puck as the projectile, the purpose of this study is to determine the effectiveness of helmet suspensions and the likelihood of skull fractures with varying conditions of head protection. An experimental arrangement is described, and the strain-gauge technique yields reliable, reproducible results. Peak stresses occur above the orbit and in the temporal regions, which agrees with previous investigations. A massive, flexibly suspended helmet offers maximum protection from fracture-inducing blows, but is probably impracticable for other reasons. A limited system analysis has corroborated the experimental results.     

Characterization and comparative expression of zebrafish calpain system genes during early development

The classic calpain system has been implicated in regulating a variety of cellular processes including cell adhesion, migration, and intracellular signaling; however, little is known regarding the function of this system in vivo. Two heterodimeric Ca(2+)-dependent cysteine proteases, mu-calpain (CAPN1) and m-calpain (CAPN2), and the endogenous inhibitor calpastatin (CAST) comprise the classic/ubiquitous calpain system in mammals. Recently, knockout of two murine classic calpain genes, Capn2 and Capn4/Capns1, revealed that components of the classic system are indispensable for preimplantation development. We identified four classic calpain catalytic subunit genes (capn1a, 1b, 2a, 2b), two regulatory subunit genes (capns1a, 1b), and calpastatin (cast) from the zebrafish. Our data suggest that the components of the classic mammalian system are both conserved and expanded in the teleost lineage. In contrast to the classic/ubiquitous mammalian system, zebrafish calpain system genes acquire unique, tissue-specific patterns of expression within the first 2 days of development.     

Clinical and socioeconomic impact of pediatric seasonal and pandemic influenza

Influenza is frequent among otherwise healthy day-care and school-aged children. Recent studies have demonstrated its significant effect on various outcome factors, including significantly more school and parental work absenteeism, and secondary illnesses among family members. Other studies have shown that the potential benefit of vaccinating children against influenza extends to other members of their families, thus supporting earlier economic modeling analyses of immunization programs. Although there are some differences in the clinical and socio-economic impact of seasonal and pandemic influenza, the benefits of vaccination are similar in both cases. The vaccination of otherwise healthy children may significantly reduce direct and indirect influenza-related costs, which supports the recommendation to make wider use of influenza vaccine in healthy children of any age in order to reduce the burden of infection on the community.     

Custom-molded foot-orthosis intervention and multisegment medial foot kinematics during walking

Context:

Foot-orthosis (FO) intervention to prevent and treat numerous lower extremity injuries is widely accepted clinically. However, the results of quantitative gait analyses have been equivocal. The foot models used, participants receiving intervention, and orthoses used might contribute to the variability.

Objective:

To investigate the effect of a custom-molded FO intervention on multisegment medial foot kinematics during walking in participants with low-mobile foot posture.

Design:

Crossover study.

Setting:

University biomechanics and ergonomics laboratory.

Patients or Other Participants:

Sixteen participants with low-mobile foot posture (7 men, 9 women) were assigned randomly to 1 of 2 FO groups.

Interventions :

After a 2-week period to break in the FOs, individuals participated in a gait analysis that consisted of 5 successful walking trials (1.3 to 1.4 m/s) during no-FO and FO conditions.

Main Outcome Measure(s):

Three-dimensional displacements during 4 subphases of stance (loading response, mid-stance, terminal stance, preswing) were computed for each multisegment foot model articulation.

Results:

Repeated-measures analyses of variance (ANOVAs) revealed that rearfoot complex dorsiflexion displacement during midstance was greater in the FO than the no-FO condition (F_1,14 = 5.24, P = .04, partial η² = 0.27). Terminal stance repeated-measures ANOVA results revealed insert-by-insert condition interactions for the first metatarsophalangeal joint complex (F_1,14 = 7.87, P = .01, partial η² = 0.36). However, additional follow-up analysis did not reveal differences between the no-FO and FO conditions for the balanced traditional orthosis (F_1,14 = 4.32, P = .08, partial η² = 0.38) or full-contact orthosis (F_1,14 = 4.10, P = .08, partial η² = 0.37).

Conclusions:

Greater rearfoot complex dorsiflexion during midstance associated with FO intervention may represent improved foot kinematics in people with low-mobile foot postures. Furthermore, FO intervention might partially correct dys-functional kinematic patterns associated with low-mobile foot postures.