Multijoint muscle regulation mechanisms examined by measured human arm stiffness and EMG signals. (9/2578)

Stiffness properties of the musculo-skeletal system can be controlled by regulating muscle activation and neural feedback gain. To understand the regulation of multijoint stiffness, we examined the relationship between human arm joint stiffness and muscle activation during static force control in the horizontal plane by means of surface electromyographic (EMG) studies. Subjects were asked to produce a specified force in a specified direction without cocontraction or they were asked to keep different cocontractions while producing or not producing an external force. The stiffness components of shoulder, elbow, and their cross-term and the EMG of six related muscles were measured during the tasks. Assuming that the EMG reflects the corresponding muscle stiffness, the joint stiffness was predicted from the EMG by using a two-link six-muscle arm model and a constrained least-square-error regression method. Using the parameters estimated in this regression, single-joint stiffness (diagonal terms of the joint-stiffness matrix) was decomposed successfully into biarticular and monoarticular muscle components. Although biarticular muscles act on both shoulder and elbow, they were found to covary strongly with elbow monoarticular muscles. The preferred force directions of biarticular muscles were biased to the directions of elbow monoarticular muscles. Namely, the elbow joint is regulated by the simultaneous activation of monoarticular and biarticular muscles, whereas the shoulder joint is regulated dominantly by monoarticular muscles. These results suggest that biarticular muscles are innervated mainly to control the elbow joint during static force-regulation tasks. In addition, muscle regulation mechanisms for static force control tasks were found to be quite different from those during movements previously reported. The elbow single-joint stiffness was always higher than cross-joint stiffness (off-diagonal terms of the matrix) in static tasks while elbow single-joint stiffness is reported to be sometimes as small as cross-joint stiffness during movement. That is, during movements, the elbow monoarticular muscles were occasionally not activated when biarticular muscles were activated. In static tasks, however, monoarticular muscle components in single-joint stiffness were increased considerably whenever biarticular muscle components in single- and cross-joint stiffness increased. These observations suggest that biarticular muscles are not simply coupled with the innervation of elbow monoarticular muscles but also are regulated independently according to the required task. During static force-regulation tasks, covariation between biarticular and elbow monoarticular muscles may be required to increase stability and/or controllability or to distribute effort among the appropriate muscles.  (+info)

Quantization of continuous arm movements in humans with brain injury. (10/2578)

Segmentation of apparently continuous movement has been reported for over a century by human movement researchers, but the existence of primitive submovements has never been proved. In 20 patients recovering from a single cerebral vascular accident (stroke), we identified the apparent submovements that composed a continuous arm motion in an unloaded task. Kinematic analysis demonstrated a submovement speed profile that was invariant across patients with different brain lesions and provided experimental verification of the detailed shape of primitive submovements. The submovement shape was unaffected by its peak speed, and to test further the invariance of shape with speed, we analyzed movement behavior in a patient with myoclonus. This patient occasionally made involuntary shock-like arm movements, which occurred near the maximum capacity of the neuromuscular system, exhibited speed profiles that were comparable to those identified in stroke patients, and were also independent of speed.  (+info)

Atypical form of amyotrophic lateral sclerosis. (11/2578)

OBJECTIVE: To investigate patients with an unusual type of muscular atrophy confined to the upper limbs (proximally dominant) and the shoulder girdle, while sparing the face and the legs until the terminal stage. METHODS: Eight patients (six men and two women) were clinically examined. The age at onset ranged from 42 to 73 years, and the clinical course varied from 28 to 81 months. There was no family history of motor neuron disease in any of these patients. Necropsy was performed in two of them. RESULTS: All eight patients basically showed a similar distribution of muscular weakness and atrophy. Subluxation of the shoulder joints was found in all patients. Reflexes were absent in the upper limbs in all patients, but were almost normal in the face and legs in most patients. Pathological reflexes could be elicited in only one patient. Electromyography showed typical neurogenic changes in the limbs of all patients. Cervical MRI disclosed moderate spondylotic changes in seven patients. Antiganglioside antibodies were negative in six patients tested. Abnormal trinucleotide (CAG) repeat expansion of androgen receptor gene was not recognised in five patients examined. Bulbar involvement developed in three patients during the course of the disease. At necropsy, one patient showed degeneration of the pyramidal tracts and motor cortex including Betz cells as well as loss of spinal anterior horn cells and brainstem motor neurons, which is consistent with ALS; in another patient there was neuronal loss of anterior horn cells at the spinal cord accompanied by astrogliosis, whereas the motor cortex and brainstem motor nuclei were relatively well preserved. Intracytoplasmic inclusions such as Bunina bodies, skein-like inclusions, and Lewy body-like inclusions were found in both patients. CONCLUSION: These patients with their peculiar pattern of muscular atrophy seem to have ALS or a subtype of ALS.  (+info)

Comparison of microvascular filtration in human arms with and without postmastectomy oedema. (12/2578)

Oedema is caused by impaired lymphatic drainage and/or increased microvascular filtration. To assess a postulated role for the latter in postmastectomy oedema, filtration was studied in the forearms of 14 healthy subjects and 22 patients with chronic, unilateral arm oedema caused by surgical and radiological treatment for breast cancer. A new non-contact optical device (the Perometer) and a conventional mercury strain gauge were used simultaneously to record forearm swelling rates caused by microvascular filtration during applied venous congestion. Filtration rate (FR) per 100 ml tissue was measured over 10-15 min at a venous pressure of 30 cmH2O, a pressure reached in the dependent forearm (FR30), and then at 60 cmH2O (FR60). Apparent filtration capacity of 100 ml soft tissue (CFCa) was calculated from FR60 - FR30/30, after adjustment for bone volume. The Perometer and strain gauge gave similar results in normal and oedematous arms. Mean CFCa in healthy subjects was (3.8+/-0.4) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1, close to literature values. In the patients, FR30 was 47 % lower in the oedematous forearm than in the opposite, unaffected forearm (P = 0.04). FR60 showed a similar trend but did not reach significance (P = 0.15). The values of CFCa of (2.2+/-0.5) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1 in the oedematous arm and (2.8+/-0.5) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1 in the unaffected arm were not significantly different (P = 0.47). When differences in arm volume on the two sides were taken into account, the total fluid load on the lymphatic system of the oedematous forearm was (411.0+/-82.2) x 10(-3) ml min-1 at 30 cmH2O and (1168+/-235.6) x 10(-3) ml min-1 at 60 cmH2O, similar to the normal side, namely (503.7+/-109.3) 10(-3) ml min-1 and (1063+/-152.0) x 10(-3) ml min-1, respectively (P >/= 0.50). The filtration capacity of the entire oedematous forearm (CFCa scaled up by total soft tissue volume), (25.4+/-6.2) x 10(-3) ml cmH2O-1 min-1, was not significantly greater than that of the normal forearm, (18.3+/-2.6) x 10(-3) ml cmH2O-1 min-1 (P = 0.40). The results indicate that no major change occurs in the microvascular hydraulic permeability-area product of the forearm, or in the total filtration load on the lymph drainage system during dependency, in the arm with postmastectomy oedema compared with the normal arm. This argues against a significant haemodynamic contribution to postmastectomy oedema.  (+info)

Long-term results and outcomes of crossover axilloaxillary bypass grafting: A 24-year experience. (13/2578)

OBJECTIVE: The outcome of crossover axilloaxillary bypass grafting in patients with stenosis or occlusion of the innominate or subclavian arteries was investigated. METHODS: The study was designed as a retrospective clinical study in a university hospital setting with 61 patients as the basis of the study. Fifty-eight patients (95.1%) had at least two risk factors or associated medical illnesses for atherosclerosis, and 35 patients (57.4%) had concomitant carotid artery stenosis that necessitated a staged procedure in 12 patients (19.7%). The patients underwent a total of 63 crossover axilloaxillary bypass grafting procedures. Demographics, risk factors and associated medical illnesses, preoperative symptoms and angiographic data, blood flow inversion in the vertebral artery, concomitant carotid artery disease, graft shape, caliber and material, and intraoperative and postoperative complications were studied to assess the specific influence in determining the outcome. RESULTS: One postoperative death (1.6%), four early graft thromboses (6.2%), and six minor complications (9. 8%) occurred. The overall mortality and morbidity rates were 1.6% and 16.1%, respectively. During the follow-up period (mean, 97.3 +/- 7.9 months), we observed five graft thromboses (8.3%). Primary and secondary patency rates at 5 and 10 years were 86.5% and 82.8% and 88.1% and 84.3%, respectively. Overall, two patients (3.3%) had recurrence of upper limb symptoms and none had recurrence of symptoms in the carotid or vertebrobasilar territory. The 5-year and 10-year symptom-free interval rates were 97.7% and 93.5%, respectively. Nine patients (15%) died of unrelated causes. The 5-year and 10-year survival rates were 93.2% and 67.3%, respectively. Multivariate analysis showed that no specific variables exerted an influence in the short-term and long-term results and the outcome. CONCLUSION: The optimal outcome of axilloaxillary bypass grafting supports its use as the most valuable surgical alternative to transthoracic anatomic reconstructions for innominate lesion, long stenosis of the subclavian artery, and short subclavian artery stenosis associated with ispilateral carotid artery lesions.  (+info)

Quantitative examinations of internal representations for arm trajectory planning: minimum commanded torque change model. (14/2578)

Quantitative examinations of internal representations for arm trajectory planning: minimum commanded torque change model. A number of invariant features of multijoint planar reaching movements have been observed in measured hand trajectories. These features include roughly straight hand paths and bell-shaped speed profiles where the trajectory curvatures between transverse and radial movements have been found to be different. For quantitative and statistical investigations, we obtained a large amount of trajectory data within a wide range of the workspace in the horizontal and sagittal planes (400 trajectories for each subject). A pair of movements within the horizontal and sagittal planes was set to be equivalent in the elbow and shoulder flexion/extension. The trajectory curvatures of the corresponding pair in these planes were almost the same. Moreover, these curvatures can be accurately reproduced with a linear regression from the summation of rotations in the elbow and shoulder joints. This means that trajectory curvatures systematically depend on the movement location and direction represented in the intrinsic body coordinates. We then examined the following four candidates as planning spaces and the four corresponding computational models for trajectory planning. The candidates were as follows: the minimum hand jerk model in an extrinsic-kinematic space, the minimum angle jerk model in an intrinsic-kinematic space, the minimum torque change model in an intrinsic-dynamic-mechanical space, and the minimum commanded torque change model in an intrinsic-dynamic-neural space. The minimum commanded torque change model, which is proposed here as a computable version of the minimum motor command change model, reproduced actual trajectories best for curvature, position, velocity, acceleration, and torque. The model's prediction that the longer the duration of the movement the larger the trajectory curvature was also confirmed. Movements passing through via-points in the horizontal plane were also measured, and they converged to those predicted by the minimum commanded torque change model with training. Our results indicated that the brain may plan, and learn to plan, the optimal trajectory in the intrinsic coordinates considering arm and muscle dynamics and using representations for motor commands controlling muscle tensions.  (+info)

Dynamic representation of eye position in the parieto-occipital sulcus. (15/2578)

Dynamic representation of eye position in the parieto-occipital sulcus. Area V6A, on the anterior bank of the parieto-occipital sulcus of the monkey brain, contains neurons sensitive both to visual stimulation and to the position and movement of the eyes. We examined the effects of eye position and eye movement on the activity of V6A neurons in monkeys trained to saccade to and fixate on target locations. Forty-eight percent of the neurons responded during these tasks. The responses were not caused by the visual stimulation of the fixation light because extinguishing the fixation light had no effect. Instead the neurons responded in relation to the position of the eye during fixation. Some neurons preferred a restricted range of eye positions, whereas others had more complex and distributed eye-position fields. None of these eye-related neurons responded before or during saccades. They all responded postsaccadically during fixation on the target location. However, the neurons did not simply encode the static position of the eyes. Instead most (88%) responded best after the eye saccaded into the eye-position field and responded significantly less well when the eye made a saccade that was entirely contained within the eye-position field. Furthermore, for many eye-position cells (45%), the response was greatest immediately after the eye reached the preferred position and was significantly reduced after 500 ms of fixation. Thus these neurons preferentially encoded the initial arrival of the eye into the eye-position field rather than the continued presence or the movement of the eye within the eye-position field. Area V6A therefore contains a representation of the position of the eye in the orbit, but this representation appears to be dynamic, emphasizing the arrival of the eye at a new position.  (+info)

Do arm postures vary with the speed of reaching? (16/2578)

Do arm postures vary with the speed of reaching? For reaching movements in one plane, the hand has been observed to follow a similar path regardless of speed. Recent work on the control of more complex reaching movements raises the question of whether a similar "speed invariance" also holds for the additional degrees of freedom. Therefore we examined human arm movements involving initial and final hand locations distributed throughout the three-dimensional (3D) workspace of the arm. Despite this added complexity, arm kinematics (summarized by the spatial orientation of the "plane of the arm" and the 3D curvature of the hand path) changed very little for movements performed over a wide range of speeds. If the total force (dynamic + quasistatic) had been optimized by the control system (e.g., as in a minimization of the change in joint torques or the change in muscular forces), the optimal solution would change with speed; slow movements would reflect the minimal antigravity torques, whereas fast movements would be more strongly influenced by dynamic factors. The speed-invariant postures observed in this study are instead consistent with a hypothesized optimization of only the dynamic forces.  (+info)