Search

Hyperkalemia is known as a major adverse effect of nafamostat, a serine protease inhibitor, and its mechanism is thought as inhibition of an amiloride-sensitive Na＋ channel. Kallikrein is a serine protease and can activate the amiloride-sensitive Na＋ channel. The study examined whether urine potassium excretion and kallikrein activity decrease in a nafamostat-induced hyperkalemia model. First, rats were administered nafamostat（1.2 mg/kg/h）or 5％ glucose by a continuous intravenous infusion（c.i.）under general anesthesia, and urine and blood samples were collected every 15 minutes from 30 minutes before until 90 minutes after drug administration. Next, nafamostat（0.13, 0.4, 1.2 mg/kg/h c.i.）or 5％ glucose was co-administered by a low-dose amiloride（3.33 µg/kg i.v. followed by 12 µg/kg/h c.i.）in the same time course. Changes in Δ serum potassium concentrations, a difference from the baseline, and those in urine potassium excretion and kallikrein activity, and their means of the last three points were evaluated. Statistical analyses were conducted by a repeated measure ANOVA（α＝0.05, one-tail test）. In results, increasing and decreasing trends were observed regarding with the changes in Δ potassium and potassium excretion, and their corresponding means of the last three points, respectively, in the nafamostat group compared with control group. In the next experiment, changes in the Δ serum potassium concentrations and those in urine potassium excretion, and their corresponding means of the last three points significantly increased and decreased, respectively, in the nafamostat group compared with the control group. A significant decrease in urine kallikrein activity was shown by the maximum dose of nafamostat regarding with the means of the last three points compared to the control. In conclusions, nafamostat induced renal hyperkalemia in vivo via inhibition of the amiloride-sensitive Na＋ channel, which was associated with inhibition of urine kallikrein activity.

To determine the foot kinematics of the depth-jump in healthy adults. We examined the usefulness of a multi-segment foot model for a movement that requires impact absorption and force exertion on the foot. Twenty healthy adults (ten men, ten women) performed a depth-jump from a 40-cm height box on to force plates. We analyzed foot motion on the landing and jump preparation phases using the Rizzoli Foot Model. A pattern of foot motion was observed during the depth-jump. Although there were no differences of the foot structure at the static standing position with respect to sex, the maximum angle of the medial longitudinal arch (MLA) in the landing phase was significantly greater in women than in men (p = 0.017). The maximum angle of the MLA in the landing phase was strongly negatively correlated with the jump height (r = − 0.6, p = 0.05). By using a multi-segment foot model, it was possible to observe a common foot motion pattern among subjects, even during a quick movement such as the depth-jump. We suggest that motion analysis using the multi-segment foot model will be useful in evaluating the foot functions of impact absorption and force exertion during a dynamic movement such as the depth-jump.

During walking, the slip velocity relative to the center of mass velocity can be one of the determinants of falls. We hypothesized that participants would select their strategy (classified by strategy type and measured by the distance of recovery landing or next forward stepping) according to both walking velocity and stance of legs. This study aimed to assess the relationship between the walking velocity relative to the slip velocity (maximum 1.6 m/s) and the corrective response and evaluated the element of the posture at the moment of slipping associated with the corrective response. Ten healthy young adults showed leading leg perturbation in two isolated velocity conditions during over ground walking (slow: 0.9 m/s, fast: 1.6 m/s) using a built-in, double-belt treadmill. We defined the corrective response to perturbation as the change in the heel marker distance post-perturbation. We examined the postural parameters affecting the difference in corrective response. During fast walking, at a velocity near the maximum slip velocity, all participants overcame slipping and kept walking. During slow walking, at a velocity less than the maximum slip velocity, most of the participants took wide steps or stepped backwards and stopped walking. During slow walking, the step length (r = 0.84, p

Background Adaptation to split-belt treadmill walking differs between individual stroke survivors. Many discussions only address spatiotemporal parameters that are related to movement, and the changes in interlimb spatiotemporal parameters as a consequence of adaptation are poorly understood. Objectives To investigate symmetry of the center of pressure (CoP) position relative to the center of mass (CoM), and ascertain whether this can be used to identify differences in adaptation of interlimb spatiotemporal parameters among stroke survivors during split-belt walking. Methods Twenty-two chronic post-stroke patients and nine elderly controls walked in tied- then split-belt (2:1 ratio of fast:slow) conditions. Spatiotemporal parameters were compared within groups to assess symmetry of the CoM-CoP angle at foot contact. Results Asymmetry of the CoM-CoP angle was associated with asymmetry of spatiotemporal parameters. Re-establishment of symmetry of CoM-CoP angle was reflected in re-established symmetry of spatiotemporal parameters in post-stroke and control participants. Conclusions Post-stroke patients who re-establish symmetry of the COM-COP angle are able to adapt their walking for split-belt perturbation. This suggests that predictively symmetric foot placements on the fast and slow sides are necessary for adaptation in walking. Symmetrical foot placement is achieved by interlimb coordination and may contribute to dynamic stability.

Objective: To clarify whether there are any muscle synergy changes in individuals with knee osteoarthritis, and to determine whether muscle synergy analysis could be applied to other musculoskeletal diseases. Methods: Subjects in this study included 11 young controls (YC), 10 elderly controls (EC), and 10 knee osteoarthritis patients (KOA). Gait was assessed on a split-belt treadmill at 3 km/h. A non-negative matrix factorization (NNMF) was applied to the electromyogram data matrix to extract muscle synergies. To assess the similarity of each module, we performed the NNMF analysis assuming four modules for all of the participants. Further, we calculated joint angles to compare the kinematic data between the module groups. Results: The number of muscle modules was significantly lower in the EC (2–3) and KOA (2–3) groups than in the YC group (3–4), which reflects the merging of late swing and early stance modules. The EC and KOA groups also showed greater knee flexion angles in the early stance phase. Contrarily, by focusing on the module structure, we found that the merging of early and late stance modules is characteristic in KOA. Conclusion: The lower number of modules in the EC and KOA groups was due to the muscle co-contraction with increased knee flexion angle. Contrarily, the merging of early and late stance modules are modular structures specific to KOA and may be biomarkers for detecting KOA. Significance: Describing the changes in multiple muscle control associated with musculoskeletal degeneration can serve as a fundamental biomarker in joint disease.

People walking on a split-belt treadmill, where each belt moves at a different speed, adapt step length to re-establish symmetry. However, kinematic changes that occur when re-establishing step length symmetry have not yet been clarified. This study aims to clarify the changing lower limb joint kinematics of each leg when re-establishing step length symmetry. We examined ten young adults who walked on a double-belt treadmill under symmetric and asymmetric conditions of belt velocity using a motion capture system. The results showed that the hip flexion angle at heel strike on one side was not significantly different between the symmetric and asymmetric conditions (p = 0.38) thereby demonstrating that the hip flexion angle of the leading leg re-established symmetry at heel strike (HS) of the fast and slow sides. However, the knee extension angle of the leading leg expanded asymmetrically at HS on both sides. The shank of the fast leg possibly accelerated more to move the heel further forward. The results indicated that subjects with limited knee extension function must increase their hip flexion movement of the fast-side limb to accelerate the shank in the swing phase. The present study suggests securing the range of motion and treatment of the knee extension to reduce the spasticity of hamstrings or plantarflexor before split-belt training. Moreover, split-belt training may be undesirable for improving step length symmetry in impaired subjects who are unlikely to improve the function of knee extension movement. The present study contributes toward developing a rehabilitation protocol that improves the gait asymmetry of patients through split-belt training.

Background Physiological evidence suggests that the nervous system controls motion by using a low-dimensional synergy organization for muscle activation. Because the muscle activation produces joint torques, kinetic changes accompanying aging can be related to changes in muscle synergies. Objectives We explored the effects of aging on muscle synergies underlying sit-to-stand tasks, and examined their relationships with kinetic characteristics. Methods Four younger and three older adults performed the sit-to-stand task at two speeds. Subsequently, we extracted the muscle synergies used to perform these tasks. Hierarchical cluster analysis was used to classify these synergies. We also calculated kinetic variables to compare the groups. Results Three independent muscle synergies generally appeared in each subject. The spatial structure of these synergies was similar across age groups. The change in motion speed affected only the temporal structure of these synergies. However, subject-specific muscle synergies and kinetic variables existed. Conclusions Our results suggest common muscle synergies underlying the sit-to-stand task in both young and elderly adults. People may actively change only the temporal structure of each muscle synergy. The precise subject-specific structuring of each muscle synergy may incorporate knowledge of the musculoskeletal kinetics.

For clinicians to provide more efficient early mobilization in patients with acute stroke, they must quantitatively evaluate the motion characteristics of the patients. To measure the motion in the acute phase, it is necessary to prevent physical interference between the measurement and medical equipment. This study classified abnormal muscle synergies during sit-to-stand motion in patients with acute stroke by using small, wirelessly operable, noninvasive surface electromyography devices. Four patients with acute stroke and four healthy adults performed a six-directional isometric contraction task and a sit-to-stand motion task. A nonnegative matrix factorization algorithm was applied to the muscle activity data to extract the muscle synergies. Hierarchical cluster analysis was used to classify these synergies. The results suggest that sit-to-stand motion characteristics according to the severity of effects in patients with acute stroke can be quantitatively classified by muscle synergy analysis. The spatial structure of muscle synergies of patients was classified into different clusters from that of the healthy adults. The abnormal muscle synergy in patients with severe paresis is considered severe in that it cannot be modulated according to the task. The muscle synergies in patients with moderate paresis were modulated in the sit-to-stand motion to compensate for extensor muscle weakness. Such abnormal muscle synergy in the sit-to-stand motion is useful as a reference for motion practice, especially for early mobilization after the onset of a stroke. In addition, the results verify that the early to late stages of recovery can be consistently evaluated with this small, wireless noninvasive electromyography device.

The aim of this study was to compare segment angles and mechanical energies obtained via inertial measurement unit (IMU) sensors attached to body segments and an optoelectronic motion capture (OMC) system during sit-to-stand motion, relevant for the assessment of movement disorder in elderly persons. seven elderly subjects were included in this study. Each subject performed sit-to-stand motions under the following two conditions: (1) rising with natural speed and posture (NORMAL) and (2) rising with trunk inclined forward (TILT). We calculated not only the segment angle but also the mechanical energy of each segment. Temporal profiles of the angles and mechanical energies of each segment were compared between the OMC data and the IMU data based on the Pearson's correlation coefficient (r) and root mean squared error (RMSE). The estimation error of the peak values of the data was also investigated with Bland-Altman bias and 95% limits of agreement. It was found that the value of r was >0.90 and the RMSE was

The main purpose of this study was to demonstrate that adaptive walking re-establishes dynamic stability at the time of foot contact in split-belt treadmill walking. First, we examined whether the relative positions of the center of mass (COM) and the center of pressure (COP) were re-established at foot contact during walking adaptation. We found that the symmetry of the COM-COP angles was re-established more completely than any other parameters (foot and pelvis markers) on both the fast and slow belt sides during the adaptation phase. Moreover, we examined whether the dynamic relationship between the COM and the COP was the same during tied- and split-belt walking. Our results showed that the equations related to the trailing leg relative to the COM re-converged around 0 at foot contact on both the fast and slow sides during the adaptation phase. We also showed that the COM-COP angle at foot contact is an adaptive parameter and is consistent between the fast and slow belt sides. At foot contact, the relative positions between the leading leg and the whole body can also be seen to be adjusted during trial-and-error adaptation to split-belt perturbation in which the belts move at different speeds. Therefore, we suggest that the relative positions of the COM and the COP at foot contact is the spatial reference for the gait cycle contribution to dynamic stabilization during adaptive walking.

Introduction/Background Sit-to-stand task is an important and kinetically challenging task for stroke patients. From the muscular strength perspective, it is well known that a large knee extension moment is required to lift the thigh. Energy flow from trunk and shank to lift the thigh has already been shown. Therefore, kinematic coordination is also necessary for the sit-to-stand task. Material and method In this study, sagittal movement onset of each segment of the body (thorax, pelvis, thigh, shank), hip joint center (HJC), and knee joint center (KJC) were compared between young (YOUNG, three people) and elderly (ELDERLY, four), and stroke patients (STROKE, three) for sit-to-stand task. We used VICON Nexus 2.5 (VICON corp.) to measure the body kinematics. Fig. 1 presents temporal order of movement onset of the body parts. The time difference within 0.005 [sec] is regarded as simultaneous, and a single quotation is added on number. The group difference existed between YOUNG and ELDERLY (e.g. mean thigh-shank was 0.13, −0.07 [s], respectively; P = 0.01). ELDERLY and STROKE (two-thirds people, paretic side) had similar timing. Conclusion In YOUNG, there is a possibility that trunk flexion lead to the translation of HJC and KJC, so that tilted the shank forward. Also, these results were consistent with a previous study that movement (work) of the trunk and shank contributes to lift the thigh. ELDERLY and some STROKE were different from this order. They may have used the movement strategy inferior in terms of energy cost, because the movement trajectory of healthy adults is controlled so that the torque of each joint is minimized. Although movement coordination is difficult to evaluate, we could provide basic knowledge from the standpoint of kinematics.

In this paper. the eccentricity factor in the progressive crushing of tubes subjected to axial compression is studied by using finite element method. It is found that the eccentricity factor is dependent on the thickness-to-radius ratio t/Ro : the eccentricity factor for a thick tube is higher than that for a thin tube. The reason why the eccentricity factor is a function of t/Ro and always takes the value of m>0.5 is related to the fact that the relations between the stress and strain are different in the outside portion and inside portion of the fold produced in the crushing. Based on the consideration of this fact, an approximation equation is proposed to evaluate change of the eccentricity factor with the tube thickness.

Vehicular mounted mobile computers are getting widely available and the DTN (Delay Tolerant Network) consisting of these vehicular computers is expected to be an information and communication infrastructure. Since distribution of the vehicular computers is not unique, the store-carry-forward approach is appropriate for high reach ability and shorter transmission delay of data messages. Though various ad-hoc and DTN routing protocols have been proposed until now, some of them requires current global information of locations and velocities of mobile wireless nodes and the others require longer transmission delay due to uncertain topology information of the network. This paper proposes a novel DTN routing approach which is a combination of street segment based route detection by using the road map information, the route selection based on transmission delay estimation along each street segment and at each intersection and the dynamic next-hop selection among the neighbor vehicular wireless nodes only by the local location information of all the neighbor ones. Due to no requirements for dynamic global information about mobile wireless network topology and to street segment based route selection, shorter transmission delay and higher reach ability is expected for the data message transmission in vehicular wireless multihop networks.

In this paper, elastoplastic post-buckling behavior of cylindrical tubes under axial compression is studied by using finite element method. In particular, the effects of tube geometries and strain hardening characteristics on the high strain concentration in circumferential direction eθ which arises at the vertex of outward wrinkles are investigated. It is found that the maximum value of eθ is dependent on the thickness-to-radius ratio t/R, and independent of the length-to-radius ratio L/R and the nondimensional hardening coefficient Eh/E. Moreover, based on our results we propose an approximation to evaluate the maximum strain eθmax by using the deformed shape of tubes. This approximation can be used to estimate the experimental results of eθmax with a good accuracy.

In this paper, elastoplastic post-buckling behavior of cylindrical tubes under axial compression is studied by using finite element method. In our study, the effects of tube geometries and strain hardening characteristics on high strain concentrations in circumferential direction eθ which arise at the vertex of outward wrinkles are investigated. It is found that the maximum value of eθ depends on the thickness-to-radius ratio t/R and the nondimentional hardening coefficient Eh /E, and independent of the length-to-radius ratio L/R. In addition, in order to evaluate the maximum strain eθ,max , the effects of tube geometries and strain hardening characteristics on the deformed shapes of folding wrinkles are also discussed.Copyright © 2004 by ASME