Yuji Ohta

A two-degree-of-freedom motor-powered gait orthosis for spinal cord injury patients:

Abstract A number of orthoses have been developed to restore stance and walking in paraplegic subjects. Compliance, however, has been limited, mainly owing to walking effort. Use of the forces produced by actuators is an effective way to solve the problem of the considerable effort required for orthotic gait, namely high muscular effort and high energy expenditure. The purpose of the present study was to investigate the effects of assistance by external actuators on the orthotic gait of spinal cord injury (SCI) patients. Two kinds of linear actuator were developed by using direct current (d.c.) motors for assisting the knee and hip joint of a gait orthosis. They were mounted on the knee and hip joint of a commercial advanced reciprocating gait orthosis (ARGO), and a new two-degree-of-freedom externally powered gait orthosis was thus developed. The orthosis was assessed through inter-subject experiments on five male adult complete SCI patients. Owing to the short training period available for the assisted gait, simultaneous operation of both joint actuators was not conducted: either the knee actuation or the hip actuation was executed only. Thus, the knee actuator and the hip actuator were assessed with a T12 subject and with subjects for T5, T8, T11, and T12 respectively. The motions of the gaits, assisted by the linear actuators, were measured by a Vicon 370 system, and the general gait parameters and compensatory motions were evaluated. Results demonstrated that (a) all subjects could walk without falling, assisted either by the knee or the hip actuator; (b) both the knee and hip joint actuator increased the gait speed and the step length; (c) the knee flexion produced by the orthosis improved the dynamic cosmesis of walking; and (d) lateral compensatory motions as well as vertical ones tended to decrease when the hip joint was assisted, which could contribute to a reduction in walking effort.

An in-shoe device to measure plantar pressure during daily human activity

In this work, we report the development of a novel device, integrated into a shoe, to monitor plantar pressure under real-life conditions by reducing the spatial and temporal resolution. The device consists of a shoe insole with seven pressure-sensitive conductive rubber sensors and a wireless data transmission unit incorporated into a smaller measurement unit. One advantage of this approach is that the mass and volume of the measurement unit are less than 1/10th and 1/50th, respectively, of that reported for other devices. A comparison experiment was conducted for validation of the device using the F-scan system, and the initial test of the device was conducted by recording unobstructed gaits of one young adult subject and two elderly subjects. Each subject performed a straight, level walking trial at a comfortable speed for 7 m without any assistive device while wearing the in-shoe device. Changes in the plantar pressure during gait were recorded. Compared with the young subject, the pressure under the heel of the elderly subject was found to be smaller and less steep. This in-shoe device can be used to monitor plantar pressure during daily living and is expected to be useful in various clinical applications.

Computer aided surgery system (CAS): Development of surgical simulation and planning system with three dimensional graphic reconstruction

To assess the feasibility of computer-aided surgery (CAS) with three-dimensional (3D) graphic reconstruction, the authors describe an experiment in which direct needle punctures were made into porcine liver phantoms on the basis of a collision assessment. A 90% success rate was achieved when a generalized cylinder method for vessel reconstruction was used. A clinical trial of this system for surgical planning shows its potential for use in abdominal surgery.<<ETX>>

Development of interactive vessel modelling system for hepatic vasculature from MR images

THREE-DIMENSIONAL reconstructions of medical images are widely used. Although there are several established techniques, if the purpose of reconstruction is only visualisation, volume rendering is the best way (CHRISTIAN, 1993). However, in applications such as surgical support, visualisation is insufficient and a more interactive approach is required. Beyond visualisation, surgical simulation is also studied, mainly in the field of plastic surgery (UDUPA et al., 1991). In this work, we describe a technique related to a system we are developing for computer-aided surgery (CAS) (Fig. 1). The system will be used in the treatment of abdominal liver cancer (DoHI et aL, 1990; HASHIMOTO et aL, 1991) and stereotactic surgery etc. For this kind of surgery, information about blood vessels is extremely important. Grasping the anatomical structure of vessel data is indispensible. Therefore, we have developed an algorithm for hepatic vasculature reconstruction which is simple, quick and quantitative. 2 M a t e r i a l s and m e t h o d s

Enhanced stretch reflex excitability in the soleus muscle during passive standing posture in humans

The purpose of this study was to test whether the spinal reflex excitability of the soleus muscle is modulated as posture changes from a supine to a passive upright position. Eight healthy subjects (29.6+/-5.4 yrs) participated in this study. Stretch and H-reflex responses were elicited while the subjects maintained passive standing (ST) and supine (SP) postures. The passive standing posture was accomplished by using a gait orthosis to which a custom-made device was mounted to elicit stretch reflex in the soleus muscle. This orthosis makes it possible to elicit stretch and H-reflexes without background muscle activity in the soleus muscle. The results revealed that the H-reflex amplitude in the ST was smaller than that in the SP condition, which is in good agreement with previous reports. On the other hand, the stretch reflex was significantly larger in the ST than in the SP condition. Since the experimental conditions of both the stretch and H-reflex measurements were exactly the same, the results were attributed to differences in the underlying neural mechanisms of the two reflex systems: different sensitivity of the presynaptic inhibition onto the spinal motoneuron pool and/or a change in the muscle spindle sensitivity.

Changes in surface roughness of erythrocytes due to shear stress: atomic force microscopic visualization of the surface microstructure.

Abstract Blood cells are subject to various kinds of stresses in flow fields. Hemolysis is the phenomenon in which a higher stress than normal damages the erythrocyte membrane and results in the leakage of its contents. Even if the stress is not strong enough to cause cell lysis, however, the cell membrane may sustain some damage. Therefore, to further improve the blood compatibility of artificial organs, the mechanisms of sublethal damage must be investigated. As a first step, we have analyzed the fine surface structure of sheared erythrocytes from a microscopic viewpoint by using an atomic force microscope (AFM) featuring nano meter-scale visualization. Sheep erythrocytes were sheared by a conventional cylindrical viscometer under sublethal shearing conditions. The duration of shear was set at 10 s, and the shearing rate was set at 0 (as control), 10 000, and 50 000/s. After being stressed, the cell surfaces were visualized by an AFM and the surface roughness was measured. As a result, the roughness value was found to increase with the shearing rate: 4.5 ± 1.5 nm (0/s, control), 6.9 ± 2.1 nm (10 000/s, P < 0.01), and 10.1 ± 2.4 nm (50 000/s, P < 0.01).

Human mesenchymal stem cells differentiate to epithelial cells when cultured on thick collagen gel

The stem cell niche is crucial to the control of stem cell fate determination in vitro as well as in vivo, and an understanding of these niches is required for the progression of stem cell and tissue engineering. The goal of our study was to commit human mesenchymal stem cells (hMSCs) to the epithelial lineage. To do this, we cultured bone marrow-derived mesenchymal stem cells (MSCs) on plates coated with type I collagen gel with or without 10 μM all-trans retinoic acid (ATRA).We found depth-dependent differentiation of hMSCs to the epithelial lineage, with the thick collagen gel (1900 μm) generating more than 80% cytokeratin-18 (CK-18)-positive cells, whereas the thin collagen gel (100 μm) generated significantly fewer CK-18-positive cells. In addition, we found that supplementation of 10 μM ATRA enhanced CK-18 expression and induced cluster-formation in cells grown on the thick collagen gel. The effect of gel depth on hMSC differentiation appears to be caused by partial cytoskeletal disruption.These results suggest that ATRA and a collagen extracellular matrix may have a synergistic effect on differentiation of human mesenchymal stem cells to epithelial lineage.

Management of surgical instruments with radio frequency identification tags

PURPOSE To prevent malpractices, medical staff has adopted inventory time-outs and/or checklists. Accurate inventory and maintenance of surgical instruments decreases the risk of operating room miscounting and malfunction. In our previous study, an individual management of surgical instruments was accomplished using Radio Frequency Identification (RFID) tags. The purpose of this paper is to evaluate a new management method of RFID-tagged instruments. DESIGN/METHODOLOGY/APPROACH The management system of RFID-tagged surgical instruments was used for 27 months in clinical areas. In total, 13 study participants assembled surgical trays in the central sterile supply department. FINDINGS While using the management system, trays were assembled 94 times. During this period, no assembly errors occurred. An instrument malfunction had occurred after the 19th, 56th, and 73 th uses, no malfunction caused by the RFID tags, and usage history had been recorded. Additionally, the time it took to assemble surgical trays was recorded, and the long-term usability of the management system was evaluated. ORIGINALITY/VALUE The system could record the number of uses and the defective history of each surgical instrument. In addition, the history of the frequency of instruments being transferred from one tray to another was recorded. The results suggest that our system can be used to manage instruments safely. Additionally, the management system was acquired of the learning effect and the usability on daily maintenance. This finding suggests that the management system examined here ensures surgical instrument and tray assembly quality.

Effects of Foot Arch Structure on Postural Stability

Background: In many human postural studies, the foot is considered to be a rigid body. The human foot is composed of the arch structure, which is characteristic in every person and deforms with aging. Foot arch structure is assumed to effect postural control; however, underlying mechanisms remain unclear. The aim of this study was to elucidate the relationship between the structure of the foot arch and postural control in the elderly. Methods: [Protocol 1] Thirty-seven healthy subjects participated in a test to determine the relationship between midfoot plantar pressure and arch height. Midfoot plantar pressure distribution (ratio of MP) was measured using the Shoe Type Stabilometer. The arch height was measured using a three-dimensional foot scanner. [Protocol 2] Ratio of MP and postural stability was measured in 143 elderly subjects using the Shoe Type Stabilometer. Postural stability was evaluated by center of pressure (CoP). Results: In Protocol 1, the correlation coefficient between the ratio of MP and ratio of arch height was r=−0.59 for the left foot and r=−0.54 for the right foot. Therefore, arch height could be predicted by ratio of MP. In Protocol 2, a significant correlation was recognized between the ratio of MP and lower limb strength, CoP total length, area anterior-posterior length, and medial-lateral (ML) length. Conclusions: The Shoe Type Stabilometer could evaluate CoP and foot arch structure. Using this device, it was found that people with a high ratio of MP, who tends to be flat-foot, displayed an increase in CoP sway. Therefore, foot arch structure contributed to postural control. Correlation between the ratio of MP and ML length, and between the ratio of MP and lower limb strength, indicated that the function of the plantar intrinsic foot muscles, which contributes to foot arch structure.

Effect of Dynamic Knee Motion on Paralyzed Lower Limb Muscle Activityduring Orthotic Gait: A Test for the Effectiveness of the Motor-Assisted Knee Motion Device

Orthotic gait in paraplegic persons is a “stiff-leg” gait, which is a gait with the knee locked in full extension position. We developed a motor-assisted knee motion device with the use of a pair of linear electric actuator attached to the knee joint of a conventional reciprocal gait orthosis (Advanced Reciprocating Gait Orthosis: ARGO). The purpose of this study was to examine the effect of dynamic knee motion on lower limb muscle electromyographic (EMG) activity during orthotic gait. Six motor complete spinal cord injured persons participated, and the subjects were asked to walk on a treadmill with two types of orthoses; Knee-ARGO and Normal-ARGO. The results demonstrated that magnitude of EMG activity in the gastrocnemius and the rectus femoris muscles was significantly increased by an accomplished dynamic knee motion. These changes might be attributed to the occurrence of an additional afferent neural input with the knee motion. The present results suggest that the assisted knee motion by generating powered device have a potential to activate the neuromuscular function in the paralyzed lower limb.