Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.10.2 (focal adhesion kinase)
44,029 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An optimal control strategy for FES-induced cyclical leg movements in paraplegics is proposed. The control of the cyclical movement of a freely swinging leg is considered as an example. Quadriceps and the flexion withdrawal reflex are stimulated in order to generate a cyclical movement, of which the forward swing resembles the swing phase of gait. Optimal stimulation patterns are determined on the basis of an optimization criterion and a dynamic model of the system. The criterion is based on desired movement parameters and a minimal duration of the stimulation bursts. The movement parameters should ensure the generation of the desired cyclical movement: a desired hip angle range, sufficient foot clearance during the forward swing and knee extension at the beginning of the backward swing. Minimal duration of the stimulation bursts is assumed to yield minimal fatigue. A dynamic model, describing the dynamics of the neural system, the muscles and the leg, was constructed and its parameters identified on the basis of preliminary experiments and literature. Optimal timing of the quadriceps and flexion reflex stimulation bursts was determined by means of computer simulation. These simulations predicted that the flexion reflex should be stimulated in a short burst approximately 150 ms before the start of the forward swing. The quadriceps should be stimulated approximately starting 200 ms before the end of the forward swing in order to ensure knee extension at the beginning of the backward swing. The duration of one cycle of the movement was between 1300 and 1500 ms in these simulations. These results predict that the movement specified by the functional objectives can be realised using only two channels of stimulation. On the basis of the optimal timing, an adaptive control strategy can be designed, which varies the stimulation burst width when muscles fatigue.
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PMID:Modelling the optimal control of cyclical leg movements induced by functional electrical stimulation. 149 50

In order to assess the effects of FES on muscle output, chronic electrical stimulation of the quadriceps muscle was applied for half an hour twice a day for 2 months, in 10 thoracic level traumatic paraplegic patients. Results concerning torque (at 6 different muscle lengths) and fatigue were measured using a strain gauge transducer in isometric condition, and compared with the findings in 15 paraplegic patients who had not received electrical stimulation, and with 10 able bodied subjects with normal motor functions. With training, muscle strength was very significantly improved whilst fatigue resistance remained at a low level. The peak torque was not found to be of the same muscle length when comparing paraplegics and control subjects; it seemed to demonstrate that length-tension relationship of the muscular actuator was changing when it was electrically activated. Moreover, the force recorded in paraplegics remained markedly lower than in able bodied people.
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PMID:Effects of functional electrical stimulation (FES) on evoked muscular output in paraplegic quadriceps muscle. 150 60

The purpose of this investigation was to see whether subject characteristics and physiologic measurements predicted exercise-heat tolerance (EHT) and voluntary tolerance time in young soldiers. A total of 18 unacclimatized males attempted six 50-min periods of treadmill walking (4.0 km.h-1, 0% grade, 33 degrees C db, 20% rh) while wearing protective overgarments. Two post hoc groups of soldiers were defined: high EHT (H) and low EHT (L), having mean (+/- S.E.) tolerance times of 360 +/- 0 and 222 +/- 12 min, respectively. Significant (p less than 0.05) H vs. L differences were observed in pretrial body mass, percent fat, and mass-to-surface area ratio (M/SA), as well as 170 min HR, Tsk and heat storage. The first three of these factors indicated that preexercise anthropomorphic characteristics may be used to distinguish H from L. The HR and Tsk differences were interpreted to mean that L experienced greater cardiovascular strain in protective overgarments because of a higher Tsk, which resulted in increased pooling of blood in cutaneous vessels, decreased cardiac filling pressure, and increased fatigue. Because HR variables were the strongest correlates of exercise tolerance time (r2 = 0.60 for HR at 170 min, r2 = 0.83 for time to reach HR of 160 beats.min-1) a novel HR monitoring technique was proposed which uses a wrist-mounted cardiotachometer to predict tolerance time.
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PMID:Prediction of the exercise-heat tolerance of soldiers wearing protective overgarments. 189 4

Hybrid FES gait restoration systems which combine stimulation with controllable mechanical damping elements at the joints show promise for providing good control of limb motion despite variations in muscle properties. In this paper we compared three controllers for position tracking of the free swinging shank in able-bodied subjects. The controllers were open-loop (OL), proportional-derivative closed-loop (PD), and bang-bang plus controlled-brake control (CB). Both OL and PD controllers contained a forward path element, which inverted a model of the electrically stimulated muscle and limb system. The CB control was achieved by maximally activating the appropriate muscle group and controlling the brake to be a "moving-wall" against which the limb pushed. The CB control resulted in superior tracking performance for a wide range of position tracking tasks and muscle fatigue states but required no calibration or knowledge of muscle properties. The disadvantages of CB control include excess mechanical power dissipation in the brake and impact forces applied to the skeletal system.
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PMID:Regulating knee joint position by combining electrical stimulation with a controllable friction brake. 228 82

This paper describes and discusses the employment of EMG pattern analysis to provide upper-motor-neuron paraplegics with patient-responsive control of FES (functional electrical stimulation) for the purpose of walker-supported walking. The system described employs above-lesion surface EMG signals to activate standing and walking functions in a patient-responsive manner. This system has been experimentally applied to paraplegics at Michael Reese Hospital and Medical Center in Chicago since early 1982. Below-lesion response-EMG control from the stimulated sites has been added in 1987 to regulate stimuli levels in the face of fatigue. Although transcutaneous FES alone is being employed, the system is applicable in principle also to implantable FES systems.
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PMID:EMG pattern analysis for patient-responsive control of FES in paraplegics for walker-supported walking. 278 79

The purpose of this study was to describe the frequency content of the electromyogram (EMG) recorded during shivering and determine if the EMG power spectrum changed as a function of the shivering duration. Six semi-nude males were exposed to cold air (5 degrees C, 20% rh) for 80 min while quietly sitting. Rectal (Tre) and mean skin (Tsk) temperatures were recorded. Shivering of the masseter muscle was determined using bipolar surface electrodes. The EMG was amplified, recorded, and subsequently digitized at 2048 Hz. The power spectrum was calculated from eight serial 0.25s EMG samples by Fourier analysis from a frequency of 4 through 480 Hz. The eight power spectra were averaged and centroid frequency (fc) calculated. During the first 10 min of exposure, Tsk rapidly dropped from 32.6 +/- 1.6 to 26.2 +/- 1.3 degrees C, then slowly declined reaching 22.5 +/- 0.7 degrees C after 80 min. Tre rose from 37.1 +/- 0.1 to 37.4 +/- 0.1 degrees C, declining after 40 min to 37.2 +/- 0.1 degrees C. Shivering was observed within 5 min after entering the cold chamber. EMG activity after 10 min exhibited an fc of 177.2 +/- 6.2 Hz. When power was integrated over 60 Hz bandwidths, the predominant frequency band of the EMG power spectrum was 60-120 Hz. Although shivering intensity increased with time, the EMG power spectrum exhibited no significant changes. These results suggest that the EMG power spectrum during shivering did not exhibit changes characteristic of muscle fatigue or muscle cooling during the 80-min cold air exposure.
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PMID:Power spectral analysis of the surface electromyogram during shivering. 380 Aug 14

In a previous work, we studied the mechanical and the metabolic profiles of fatigue of paralyzed quadriceps muscle under activation by FES. The metabolic state of the muscle during stimulation of paraplegic patients was monitored, simultaneously with the decaying force, by using 31P nuclear magnetic resonance spectroscopy. In the present work, a musculotendon model was developed to enable prediction of the force output during continuous electrical stimulation. The model consisted of five elements, including the tendon, the parallel elastic, contractile and damper muscle elements, as well as the muscle mass. The mechanism of the contractile element was based upon the length-tension and the velocity-tension curves, the activation trajectory, and the experimentally obtained relationship between force and intracellular pH. In the equations obtained, three sets of parameters were used: 1) general muscle parameters, associated with the length-tension curves of tendon, fascia, and muscle and the velocity-tension curve of the contractile element; 2) specific anthropometric parameters of the muscle; and 3) fatigue parameters which were obtained from our previously recorded experimental data. The model was formulated to allow prediction of the quadriceps muscle force under dynamic activation and at various levels of stimulation. The model solution was for isometric contraction in supermaximal stimulation, and it provided the force decaying profiles, which were compared to those obtained experimentally. The parameters yielding the best fit between the model and the experimental results were indicated. Particularly, two muscle nonspecific parameters, namely, the muscle stress parameter and the parameter representing the ratio between the muscle's slack length and its length in vivo at various knee angles, were determined using the model. The muscle stress parameter was found to be between 60 and 64 N/cm2, and the length ratio was 0.952, 0.935, 0.920, and 0.901 for the 0, 30, 60, and 90 degrees knee angle, respectively. Finally, a sensitivity analysis was conducted of the model to perturbations of these two estimated parameters, revealing that the model was sensitive to these parameters.
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PMID:A musculotendon model of the fatigue profiles of paralyzed quadriceps muscle under FES. 824 27

A novel material called 'self-reinforced composite poly(methyl methacrylate)' (SRC-PMMA) is described. This composite material consists of high strength, high ductility PMMA fibres embedded in a matrix of PMMA. Tensile tests, three-point flexural tests, fracture toughness tests and flexural fatigue tests were carried out on unidirectional continuous fibre SRC-PMMA materials. Commercial sheet PMMA and bone cement were also tested for comparison purposes. Two PMMA fibre sizes (40 and 120 microns diameters) with different mechanical properties were used to make the SRC-PMMA materials. The results of this study show that the tensile strength, tensile modulus and tensile strain-to-failure were significantly greater for the SRC-PMMA compared with commercial PMMA (P < 0.05). The flexural strength was not increased in the SRC-PMMA compared with PMMA alone but was greater than that in bone cement (P < 0.05). There were no differences in flexural modulus between any group. The flexural strain-to-failure (30-35% for SRC-PMMA) was about three times greater in SRC-PMMA compared with bone cement and PMMA. Fracture toughness of these SRC-PMMA materials was also significantly greater than PMMA and bone cement (P < 0.001). Fracture toughness values of 3.2 MPa m1/2 were found in the 40 microns SRC-PMMA compared with 2.3 MPa m1/2 for the 120 microns SRC-PMMA and 1.3 MPa m1/2 for PMMA and bone cement. The fatigue strength of both SRC-PMMA samples was significantly greater (P < 0.001) at 80 MPa (10(6) cycles) compared with bone cement and PMMA, both of which had fatigue strengths of about 18 MPa. Fatigue damage in the form of fibre splitting and fibre-matrix interface failure was observed in the SRC-PMMA samples while the PMMA and bone cement showed only smooth fractures. During cyclic fatigue testing, the ongoing damage processes were periodically monitored using several novel computer-based and analysis algorithms. The measured cyclic loads and displacements are used to determine the creep-fatigue displacements, the sample stiffness (or modulus) and the hysteresis damage energy as functions of the number of applied cycles associated with the fatigue loading. The hysteresis damage energy to failure was about 25 times greater in the SRC-PMMA samples (2000 J at 10(6) cycles) compared with bone cement or PMMA at the same number of cycles to failure (80 J) indicating much greater fatigue damage tolerance in these materials. This material, SRC-PMMA, may be applicable for use in several medical and/or dental applications.
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PMID:Self-reinforced composite poly(methyl methacrylate): static and fatigue properties. 851 25

A cross-sectional study of a cohort of 49 male human immunodeficiency virus (HIV)-infected intravenous drug users attending the Infectious Diseases Unit of the National University of Malaysia during 1991-94 yielded a clinical profile of these patients. The mean age of respondents was 33.2 years and the mean duration of intravenous drug use was 12.7 years. On average, these men had known of their HIV-positivity for 53.2 weeks. Intravenous drug use was the only reported HIV risk factor in 34 men (69%). Clinical symptoms at intake included fatigue (49%), weight loss (47%), night sweats (31%), fever (14%), and diarrhea (6%), while clinical findings included hepatomegaly (57%), lymphadenopathy (35%), and oral thrush (29%). Anemia (82%), leucocytosis (53%), hypoalbuminemia (43%), hyperglobulinemia (88%), elevated liver enzymes and hyponatremia (57%) were frequent laboratory findings. The prevalences of hepatitis B virus, cytomegalovirus, and toxoplasma infection were 12.1%, 72.7%, and 59%, respectively. A total of 91 diagnoses were made in these 49 patients: most common were pneumonia, tuberculosis, bacteremia, infective endocardiditis, mycotic aneurysm, and psychiatric disorders. The mean duration of known progression to acquired immunodeficiency syndrome (AIDS) in the 7 patients at this stage was 391 days. Pneumocystis carinii pneumonia was the most common AIDS-defining illness. Three months into the study, 19 men (57%) had defaulted, reflecting the difficulties of involving drug addicts in research and intervention projects. Moreover, 16 patients (33%) were first confirmed HIV-positive at presentation to the hospital, suggesting that many drug users' HIV status remains unknown until they develop symptoms requiring hospital care.
Int J STD AIDS 1997 Feb
PMID:A study of Malaysian drug addicts with human immunodeficiency virus infection. 906 11

We aim to assess the age-related differences in psychological stress and depression in patients with human immunodeficiency virus (HIV) infection. Prospective, longitudinal, observational study of patients with HIV followed at a university affiliated VA Medical Center. Fifty-six consecutive patients with HIV infection aged 19-68 were studied. Data on demographics, living arrangements, education, employment, income, social, religious, and community support, medical status, psychological stress, depression, and coping was assessed at baseline and every 6 months. Instruments for psychological testing included Beck Depression Inventory, Profile Mood Status (POMS) scale and ways of coping scale (inventory of coping with illness scale). Sixty-nine per cent (38/56) of the patients were older than 35 years of age. Older patients exhibited significantly greater emotional and psychological stress; the mean POMS score for older patients was 56.8 as compared to 21.5 for younger patients (P = 0.004). Older patients had significantly greater depression (P = 0.001), higher tension and anxiety (P = 0.005), greater anger and hostility (P = 0.03), greater confusion and bewilderment (P = 0.01), and more fatigue (P = 0.003) as compared with younger patients. Older patients were significantly more likely to have intravenous drug use as an HIV risk factor (P = 0.02), less likely to be employed (P = 0.005), and more likely to use non-traditional therapies (P = 0). Intravenous drug use was an independent predictor of psychological stress in older patients. Patients with HIV, older than 35 years of age, are significantly more likely to suffer from depression and psychological stress; intravenous drug use was an independent predictor of stress. Interventions for the treatment of depression should be especially sought in this subgroup of patients with HIV.
Int J STD AIDS 1997 Apr
PMID:Psychological stress and depression in older patients with intravenous drug use and human immunodeficiency virus infection: implications for intervention. 914 58


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