Junghwa Hong

Sex differences in the postural sway characteristics of young and elderly subjects during quiet natural standing

Aim:  It has been reported that the fall incidence in women is much higher than men and that fallers have worse postural balance performance than non‐fallers. However, it is controversial whether any sex difference in postural balance performance exists. The purpose of this study was to investigate the effects of sex and age and their interactions in balance performance during quiet standing with natural stance width.

Analysis of Viscoelastic Properties of Wrist Joint for Quantification of Parkinsonian Rigidity

This study aims to analyze viscoelastic properties of the wrist in patients with Parkinsons disease (PD) in comparison with the clinical score of severity. Forty-five patients with PD and 12 healthy volunteers participated in this study. Severity of rigidity at the wrist was rated by a neurologist just before the experiment. Wrist joint torque resistive to the imposed movement was measured. Three different models, (identical in structure, only different in the number of parameters for extension and flexion phases) were used in identification of viscoelastic properties: 1) one damping constant and one spring constant throughout all phases, 2) two damping constants for each phase and one spring constant throughout all phases, and 3) two damping constants and two spring constants for each phase. Normalized work and impulse suggested in the literature were also calculated. Spring constants of different models and phases showed comparable correlation with rigidity score ( r=0.68-0.73). In terms of the correlation of damping constant with clinical rigidity score, model 1 ( r = 0.90) was better than models 2 and 3 ( r=0.59 - 0.71). These results suggest that the clinical rigidity score is better represented by the mean viscosity during both flexion and extension. In models with two dampers (model 2 and 3), the damping constant was greater during extension than flexion in patients ( p <; 0.001), in contrast that there was no phase difference in normal subjects. This suggests that in contrast with normal subjects, phase-dependent viscosity may be an inherent feature of PD. Although work and impulse were correlated with clinical rigidity score ( r = 0.11 - 0.84), they could not represent the phase-dependent rigidity inherent in PD. In conclusion, the viscosity of model 1 would be appropriate for quantification of clinical ratings of rigidity and that of model 2 for distinction of PD and also for investigation of phase-dependent characteristics in parkinsonian rigidity.

Age-gender differences in the reaction times of ankle muscles.

Reaction times of the hip abductor were reported to be longer in elderly women than in elderly men, and this was suggested to be related to mediolateral balance performance. The aim of the present study was to investigate the effects of age and gender on the reaction performance of ankle muscles, which have predominant roles in anterioposterior balance control.

Quantitative electromyographic analysis of reaction time to external auditory stimuli in drug-naïve Parkinson's disease.

Evaluation of motor symptoms in Parkinsons disease (PD) is still based on clinical rating scales by clinicians. Reaction time (RT) is the time interval between a specific stimulus and the start of muscle response. The aim of this study was to identify the characteristics of RT responses in PD patients using electromyography (EMG) and to elucidate the relationship between RT and clinical features of PD. The EMG activity of 31 PD patients was recorded during isometric muscle contraction. RT was defined as the time latency between an auditory beep and responsive EMG activity. PD patients demonstrated significant delays in both initiation and termination of muscle contraction compared with controls. Cardinal motor symptoms of PD were closely correlated with RT. RT was longer in more-affected side and in more-advanced PD stages. Frontal cognitive function, which is indicative of motor programming and movement regulation and perseveration, was also closely related with RT. In conclusion, greater RT is the characteristic motor features of PD and it could be used as a sensitive tool for motor function assessment in PD patients. Further investigations are required to clarify the clinical impact of the RT on the activity of daily living of patients with PD.

Theoretical study of the effect of piezoelectric bone matrix on transient fluid flow in the osteonal lacunocanaliculae: THEORETICAL STUDY OF THE EFFECT OF PIEZOELECTRIC BONE

A new theoretical generation mechanism of the transient streaming potential considering variations in the surface potential on the wall in a lacunocanalicular system, is proposed based on the assumption of the piezoelectric bone matrix. To obtain the streaming potential analytically, a modified transient charge density equation is proposed. An osteon is modeled as a piezoelectric solid phase having fluid‐filled cavities (lacunae) connected by channels (canaliculae) to obtain the pressure gradients in the canaliculae and the electric boundary conditions on the canalicular walls. In addition, this study focused on modeling of the negatively charged glycocalyx that fills the annular fluid space between the osteocytic process and the canalicular wall. It is assumed that the annular fluid space of the canaliculi can be represented as a two‐layer configuration for flow through a gap (between the tips of the glycocalyx and the canalicular wall) overlaying the porous glycocalyx. The transient streaming potential and bone fluid flow affected by the generated total potential are analyzed using the one‐dimensional lacunocanalicular fluid path, which is surrounded by the piezoelectric bone matrix. A significant increase in the streaming potential is predicted for the case with piezoelectricity. The peak streaming potential value with the piezoelectricity is found to be up to 58.8% greater compared with that without piezoelectricity. The electroviscous effect due to the total electric potential gradients on the fluid velocities in the canaliculi is negligible. These findings imply that the piezoelectric effect caused by deformation of the bone matrix should be considered for prediction of the streaming potential in the lacunocanaliculae.

Design of Wearable Airbag with Injury Reducing System.

Injuries caused by falls has become significant social problem in aging society. Falls could cause fractures which is significant cause of morbidity and mortality. As a result, active protecting devices are being developed to protect body from severe injuries. In this study, simulation test method of falls situation is established and the wearable airbag system for protecting from falls is designed through simulation. Ergonomic design is considered in this wearable airbag system to reduce injury level effectively. It will be possible to establish the reliability of the development of the fall prevention system for the elderly and to be the basis for the future development.

Permeability Prediction of Human Proximal Femoral Trabeculae in the Direction of Superior-to-Fovea Utilizing Directly Measured Microscopic Poroelastic Properties

Since cancellous bone remodeling is active compared to cortical bone, the fluid communications for the metabolism of osteocytes between the inter-trabecular and intra-trabecular pores should be active compared to those between the vascular and lacunocanalicular pores in osteons. In this study, the permeability coefficient of trabeculae of human proximal femur in the direction of superior-to-fovea is estimated by using the isotropic poroelasticity. Using the pore pressure solution in the drained uniaxial strain condition and the poroelastic properties of trabeculae, effects of the permeability coefficient in the direction of superior-to-fovea on intra-trabecular fluid pressure generation are investigated. In the range of the applied permeability coefficient from 10−15 to 10−10 m2/kPa-sec, the predicted maximum intra-trabecular fluid pressure was 754 kPa. The predicted range of intrinsic permeability is from 10−21 to 10−16 m2 when 0.001 Pa-sec of the dynamic viscosity of serum is used. The predicted permeability values are larger than those for cortical tissues. It was reported that the mean lacuna volumes of trabeculae and cortical tissue in the human femur ranged from 445 to 488 µm 3 and from 389 to 408µm 3, respectively.

The effect of lower limb muscle contractions on the impact acceleration behaviour of medial knee in low-speed pedestrian impact

For accurate analysis in low-speed collisions, roles of muscle in the low extremities are included in a finite element (FE) human model. The impact accelerations were estimated for vehicle-pedestrian collisions with and without muscle activations under 10 km/hour. The predicted acceleration at the medial knee was verified by the actual tests performed at 2.88 km/hour. Then, experiments were performed using a sled to obtain muscle activations, and impact accelerations of the subjects. More analyses were performed using the FE human model at 5 and 10 km/hour to understand effects of muscle activations on impact accelerations. At the lowest impact speed, the reduction of acceleration was 20% when the result with muscle activations was compared to that without muscle activations. The reduction was decreased to 12% at 5 km/hour. At 10 km/hour, the reduction was insignificant but existed to as much as 3%. Therefore, muscle activations in the lower limbs are important when the impact velocity is lower than 10 km/hour.