The dynamic flexion/extension properties of the lumbar spine in vitro using a novel pendulum system

The biomechanical properties of the ligamentous cadaver spine have been previously examined using a variety of experimental testing protocols. Ongoing technical challenges in the biomechanical testing of the spine include the application of physiologic compressive loads and the application of dynamic bending moments while allowing unconstrained three-dimensional motion. The purpose of this study was to report the development of a novel pendulum apparatus that addressed these challenges and to determine the effects of various axial compressive loads on the dynamic biomechanical properties of the lumbar functional spinal unit (FSU). Lumbar FSUs were tested in flexion and extension under five axial compressive loads chosen to represent physiologic loading conditions. After an initial rotation, the FSUs behaved as a dynamic, underdamped vibrating elastic system. Bending stiffness and coefficient of damping increased significantly as the compressive pendulum load increased. The apparatus described herein is a relatively simple approach to determining the dynamic bending properties of the FSU, and potentially disc arthroplasty devices. It is capable of applying physiologic compressive loads at dynamic rates without constraining the kinematics of the joints, crucial requirements for testing FSUs in vitro.     

Treatment of spinal spasticity by electrical stimulation

We present the results and the methodology of trials using transcutaneous electrical stimulation. The aim of our work was to decrease spasticity in 44 patients with traumatic damage to the spinal cord; 35 non-electrically stimulated spastics were used as controls. Both groups were randomly selected from inpatients in the Paraplegic Department at the Hospital Rehabilitation Centre. This electrical stimulation procedure leads to a long-lasting reduction in spasticity, an increased range of passive and active movements, the facilitation of lost functions, an improvement in breathing, an increase in pulmonary capacity, the reappearance of some neurological reflexes, and a diminution of supersensitivity to skin irritation. Blood pressure and neurogenic bladder functions were restored to normal. In addition to clinical observations, we investigated muscle force and the electromyogram; other measurements used in the trials involved the use of a specially adapted neurological hammer, a pendulum test, spirometry, cystometry, sphincterometry and biochemical estimations.     

Short-term effects of thermotherapy for spasticity on tibial nerve F-waves in post-stroke patients

Thermotherapy is generally considered appropriate for post-stroke patients with spasticity, yet its acute antispastic effects have not been comprehensively investigated. F-wave parameters have been used to demonstrate changes in motor neuron excitability in spasticity and pharmacological antispastic therapy. The present study aimed to confirm the efficacy of thermotherapy for spasticity by evaluating alterations in F-wave parameters in ten male post-stroke patients with spastic hemiparesis (mean age: 49.0±15.0 years) and ten healthy male controls (mean age: 48.7±4.4 years). The subjects were immersed in water at 41°C for 10 min. Recordings were made over the abductor hallucis muscle, and antidromic stimulation was performed on the tibial nerve at the ankle. Twenty F-waves were recorded before, immediately after, and 30 min following thermotherapy for each subject. F-wave amplitude and F-wave/M-response ratio were determined. Changes in body temperature and surface-skin temperature were monitored simultaneously. The mean and maximum values of both F-wave parameters were higher on the affected side before thermotherapy. In the post-stroke patients, the mean and maximum values of both parameters were significantly reduced after thermotherapy (P<0.01). Hence, the antispastic effects of thermotherapy were indicated by decreased F-wave parameters. Body temperature was significantly increased both immediately after and 30 min after thermotherapy in all subjects. This appeared to play an important role in decreased spasticity. Surface-skin temperature increased immediately after thermotherapy in both groups and returned to baseline 30 min later. These findings demonstrate that thermotherapy is an effective nonpharmacological antispastic treatment that might facilitate stroke rehabilitation.     

Longitudinal displacements of base pairs in DNA and effects on the dynamics of nonlinear excitations

A model of the DNA is proposed and studied analytically and numerically. The model is an extension of a well known model and describes the double helix as two chains of pendula (each pendulum representing a base). Each base (or pendulum) can rotate and translate along the helix axis. In the continuum limit the system is described by the perturbed Sine–Gordon equation describing the twist of the bases and by a nonlinear partial differential equation (PDE) describing the longitudinal displacements of the bases. This coupled system of PDEs was studied analytically using different approaches and the corresponding results were tested through numerical simulations. It was found that if the coupling parameters satisfy a well defined relationship, then there exist bounded travelling wave solutions.     

A Regression Modeling Approach for Describing Patterns of HIV Genetic Variation

We introduce a novel approach for describing patterns of HIV genetic variation using regression modeling techniques. Parameters are defined for describing genetic variation within and between viral populations by generalizing Simpson's index of diversity. Regression models are specified for these variation parameters and the generalized estimating equation framework is used for estimating both the regression parameters and their corresponding variances. Conditions are described under which the usual asymptotic approximations to the distribution of the estimators are met. This approach provides a formal statistical framework for testing hypotheses regarding the changing patterns of HIV genetic variation over time within an infected patient. The application of these methods for testing biologically relevant hypotheses concerning HIV genetic variation is demonstrated in an example using sequence data from a subset of patients from the Multicenter AIDS Cohort Study.     

An Extended Threshold Model for Analyzing Ordered Categorical Data

This paper presents an extended threshold model for analyzing ordered categorical data. The model admits interactions between the position of the thresholds and the levels of the effective factors. These interactions are described according to the approach of Milliken and Graybill (1970). Especially important for practical application is the special assumption that there is a linear relation between interactions and thresholds, and that the slopes of the concerning regression lines may be different for samples. This means that the latent variables are distributed according to the same type of distributions, but may have different expectations and variances. Underlying this submodel, the estimation of parameters and the testing of hypotheses according to the maximum likelihood method is described. The procedure is illustrated by a numerical example, and an outline is given about a cluster analysis using model parameters.     

Modeling balance control during sustained waking allows posturographic sleepiness testing

We develop a method to quantify sleepiness. Sleepiness is a major risk factor in traffic and occupational accidents, but lack of convenient tests precludes monitoring impending sleepiness. Posturographic balance testing could address this need because sleepiness increases postural sway. It is, however, unclear how sleepiness influences balance control. Our results, for 12 subjects, show that balance control is more susceptible to increasing time awake (TA) compared to neuromuscular processes. This conclusion is reached since during sustained waking the control process slows down by 3.4% per hour of increased TA. This slowdown accounts for 65% of the variance in diurnal balance. We quantified balance control by modeling the body as an inverted pendulum and by expressing the control as the critical time interval for open-loop control (Deltat(c)) of the center-of-mass movements of this pendulum. To estimate the subjects' TA, we regressed the Deltat(c) scores recorded during sustained waking against increasing TA, and equated separate Deltat(c) test scores with the diurnal Deltat(c) scores. We estimated TA with 68% positive predictive value. The results encourage implementing balance modeling into a device that performs clinical or industrial balance testing because the model-based Deltat(c) score responded to increasing TA.     

Espasticidad tras ictus: ¿la edad es un factor de riesgo? Estudio observacional de la espasticidad en pacientes neurovasculares en una serie retrospectiva de dos centros

ObjectiveApproximately one third of patients who have suffered a stroke develop spasticity. Since clinical observations that spasticity in the elderly population is lower after stroke, and disagreement about risk factors between different authors, an analysis is performed on the variables that influence the development of spasticity.The objective of the study is to determine the how many factors influence spasticity outcome, and the prevalence of spasticity in patients who have suffered a stroke and require intensive rehabilitation treatment.MethodA retrospective assessment was carried out on a total of 554 patients from two neurorehabilitation centres. A record was made of sociodemographic data, aetiology, type and location of stroke, motor and sensory deficits, language and swallowing impairment, incontinence, cognitive and mood state. Spasticity levels at admission and at the third month were studied in 462 patients using the Ashworth scale. Multivariate regression analyses were used to assess the risk factors for spasticity present at the third month after stroke.ResultsThe mean age of the patients was 67.3 years, of which 67.1% were men, and with ischemic aetiology in 76.5%. On admission 31.4% of patients had spasticity, and this increased to 54.8% at the 3^rd month. The absolute risk factor for spasticity was motor index (OR 1.04; 95% CI 1.03-1.05). When this factor was omitted, the variables with predictive ability were: age less than 75 years (OR 0.52; 95% CI 0.30-0.90), sensory impairment (OR 0.66; 95% CI 0.37-1.20), and lower Barthel index score (OR 1.02; 95% CI 1.01-1.03). There was no significant relationship for gender, physiopathological mechanism (ischaemic/haemorrhagic), stroke location, aphasia, or cognitive impairment.ConclusionThe prevalence of spasticity in stroke at third month of follow-up was 54.8%. Motor index is the independent predictor of spasticity. Patients younger than 75 years old, with sensory impairment and low Barthel index score are more likely to develop spasticity.     

Beneficial effects of footbaths in controlling spasticity after stroke

Footbaths are considered to provide beneficial thermal therapy for post-stroke patients with spasticity, but their anti-spastic effects have not been investigated comprehensively. The present study aimed to evaluate alterations in motor-neuron excitability using F-wave parameters in post-stroke patients with spastic hemiplegia. Subjects’ legs below the knee joint were immersed in water at 41°C and F-wave recordings were made over the abductor hallucis muscle before, immediately after, and 30 min after thermal treatment. Antidromic stimulation was performed on the tibial nerve at the ankle. Measurements included F-wave amplitude, F-wave/M-response ratio, changes in modified Ashworth scale (MAS), body temperature and surface-skin temperature. The mean values of both F-wave parameters were higher on the affected side before footbath treatment. In post-stroke patients, the mean values of F-wave parameters were significantly reduced after footbath treatment (P < 0.01). The anti-spastic effects of footbath treatment were indicated by decreased F-wave parameters, in parallel with decreases in MAS. Body temperature was significantly increased both immediately after, and 30 min following footbath treatment in both groups, which appeared to play an important role in decreased spasticity. Surface-skin temperature increased immediately after footbath treatment in both groups and returned to baseline 30 min later. These findings demonstrate that the use of footbaths is an effective nonpharmacological anti-spastic treatment that might facilitate stroke rehabilitation.     

A new test set-up for skull fracture characterisation

Skull fracture is a frequently observed type of severe head injury. Historically, a variety of impact test set-ups and techniques have been used for investigating skull fracture. The most frequently used are the free-fall technique, the guided fall or drop tower set-up and the piston-driven impactor set-up. This document proposes a new type of set-up for cadaver head impact testing which combines the strengths of the most frequently used techniques and devices. The set-up consists of two pendulums, which allow for a 1 degree of freedom rotational motion. The first pendulum is the impactor and is used to strike the blow. The head is attached to the second pendulum using a polyester resin. Local skull deformation and impact force are measured with a sample frequency of 65 kHz. From these data, absorbed energy until skull fracture is calculated. A set-up evaluation consisting of 14 frontal skull and head impact tests shows an accurate measurement of both force and local skull deformation until fracture of the skull. Simplified mechanical models are used to analyse the different impacting techniques from literature as well as the new proposed set-up. It is concluded that the proposed test set-up is able to accurately calculate the energy absorbed by the skull until fracture with an uncertainty interval of 10%. Second, it is concluded that skull fracture caused by blunt impact occurs before any significant motion of the head. The two-pendulum set-up is the first head impact device to allow a well-controlled measurement environment without altering the skull stress distribution.     

Identifying the brain regions associated with acute spasticity in patients diagnosed with an ischemic stroke

Spasticity is a common impairment found in patients that have been diagnosed with a stroke. Little is known about the pathophysiology of spasticity at the level of the brain. This retrospective study was performed to identify an association between the area of the brain affected by an ischemic stroke and the presence of acute spasticity. Physical and occupational therapy assessments from all patients (n?=?441) that had suffered a stroke and were admitted into a local hospital over a 4-year period were screened for inclusion in this study. Subjects that fit the inclusion criteria were grouped according to the presence (n?=?42) or absence (n?=?129) of acute spasticity by the Modified Ashworth Scale score given during the hospital admission assessment. Magnetic resonance images from 20 subjects in the spasticity group and 52 from the control group were then compared using lesion density plots and voxel-based lesion–symptom mapping. An association of acute spasticity with the gray matter regions of the insula, basal ganglia, and thalamus was found in this study. White matter tracts including the pontine crossing tract, corticospinal tract, internal capsule, corona radiata, external capsule, and the superior fronto-occipital fasciculus were also found to be significantly associated with acute spasticity. This is the first study to describe an association between a region of the brain affected by an infarct and the presence of acute spasticity. Understanding the regions associated with acute spasticity will aid in understanding the pathophysiology of this musculoskeletal impairment at the level of the brain.     

SPASTICITY—Its Nature and Treatment

There are a number of physiological means of relaxing spasticity, including active resistive exercise, cold hydrotherapy, heat, electrical stimulation of antagonistic muscles, passive stretch in diagonal movement patterns, and the Von Bechterew reflex. Although none of them will cure spasticity, temporary relaxation may permit a patient to achieve better functioning of an affected joint. The choice of procedure will depend on the nature of the lesion and the muscular distribution of the spasticity.     

Are clinical parameters sufficient to model gait patterns in patients with cerebral palsy using a multilinear approach?

The aim of this study was to evaluate whether clinical parameters are sufficient using, a multilinear regression model, to reproduce the sagittal plane joint angles (hip, knee, and ankle) in cerebral palsy gait. A total of 154 patients were included. The two legs were considered (308 observations). Thirty-six clinical parameters were used as regressors (range of motion, muscle strength, and spasticity of the lower). From the clinical gait analysis, the joint angles of the sagittal plane were selected. Results showed that clinical parameter does not provide sufficient information to recover joint angles and/or that the multilinear regression model is not an appropriate solution.     

Assessment of reproductive risks

In the regulatory process, the hazards posed by potentially toxic agents to the female and male reproductive systems and to developing young are evaluated by risk assessment procedures. In this paper, toxicity testing and the regulatory process are discussed, with emphasis on risk assessment. The suggested testing protocols of the Pesticide Assessment Guidelines (U.S. EPA) are presented as an example of testing that might be done to produce toxicity data for an agent. Protocols and end points that are utilized in testing for reproductive effects are described. Included are acute, subchronic, chronic, and short-term tests. The four components of reproductive risk assessment (hazard identification, dose-response assessment, exposure assessment, and risk characterization) are examined. Effects of dibromochloropropane on rabbit testicular parameters are used to demonstrate approaches that could be taken in doing a reproductive risk assessment. Research needs for screening methods, adequate dose-response testing, toxicokinetics, end point development, and extrapolation methods are identified. Finally, this paper discusses selected areas in which changes in reproductive risk assessment are anticipated, as well as the mechanism for influencing the nature and extent of those changes.     

Effect of Botulinum Toxin on Spasticity Level Assessed by Tonic Stretch Reflex Threshold: A Feasibility Pilot Study

IntroductionSpasticity is one of the most disabling neurological conditions, generally associated with pain and articular contracture. Its management involves multiple rehabilitation techniques, including botulinum toxin. Studies were developed with the intention of assessing the clinical effects of the Botulinum toxin (BoNT) injection in spastic muscles, however most of them, utilized subjective assessment methods. The aim of this study was to investigate the feasibility of applying Tonic Stretch Reflex Threshold (TSRT) method in clinical practice to assess the spasticity before and after BoNT injection and compare the results with those provided by methods traditionally used for this purpose: Modified Ashworth Scale (MAS) and Range of Motion (ROM).MethodsFive patients were evaluated before and after 21 days of BoNT injection in biceps brachii. Three parameters were considered: MAS, ROM of elbow and TSRT.ResultsAll patients presented improvement in ROM (p = 0.05) and TSRT (p = 0.06), with ROM average improvement bigger than TSRT. Two patients did not present evolution in MAS (p = 0.14).ConclusionsThe feasibility pilot study was the first to utilize the TSRT as an evaluation method after BoNT application. The TSRT method was able to identify improvement in patients that MAS did not able to, and is a good alternative to assess spasticity even when the evolution is small. Hence, TSRT showed to be an effective method for monitoring more precisely spasticity in BoNT treatment.     

Spasticity; its nature and treatment

There are a number of physiological means of relaxing spasticity, including active resistive exercise, cold hydrotherapy, heat, electrical stimulation of antagonistic muscles, passive stretch in diagonal movement patterns, and the Von Bechterew reflex. Although none of them will cure spasticity, temporary relaxation may permit a patient to achieve better functioning of an affected joint. The choice of procedure will depend on the nature of the lesion and the muscular distribution of the spasticity.     

A computational human model for exploring the role of the feet in balance

Many studies concerning human balance use computational models that represent the body as a single, double, or triple inverted pendulum while ignoring the feet. Clinical research, however, has begun to more closely examine specific contributions of the feet in balance, leading to a disparity between the state of clinical research and the models used for simulation. Here, we expand the single inverted pendulum model by adding four additional rigid links to represent the feet. Model parameters, equations of motion, actuation based on human musculature, and control based on proprioception are discussed. Computation of ground reaction forces under the heel, forefoot, and toes is also addressed. Simulations focusing on the role of the toes and toe muscles in static balance and forward leaning are presented.     

Genetic relationship of catalepsy to penduliform movements and audiogenic epilepsy in rats

Within outbred Wistar stock, the pendulum movements are found to be inherited in what may be considered as a dominant mono- or oligogenic mode of inheritance with incomplete penetrance. This indicates that the albinism only permits the manifestation of the pendulum movements, which are also controlled by some other gene or genes. The pendulum movements show a positive genetic relation to catalepsy, although this relation is not strong: the proportion of animals with pendulum movements is 23% in the control population and 32% in F12-F16 bred for catalepsy (p less than 0.05). Within the latter, the proportion of animals with pendulum movements was 43% in the progeny of parents with phenotypically expressed catalepsy, and 29% in the progeny of phenotypically "normal" animals (p less than 0.01). The frequency of audiogenic seizures was 32% in the control population and 17% in F8-F16 bred for catalepsy (p less than 0.001). A genetic model is proposed to account for the paradoxical situation, where pendulum movements have a positive genetic relation both to catalepsy and audiogenic epilepsy, the catalepsy being at the same time negatively related to epilepsy.     

Pharmacological characteristics of the ganglionic and aganglionic colon in Hirschsprung's disease.

The pharmacological characteristics of circular and longitudinal muscle strips from normal and aganglionic colon were investigated in vitro in 13 patients with Hirschsprung's disease. The sensitivity for acetylcholine, noradrenaline and isoprenaline is normal in aganglionic tissue. Betanechol, carbacholine, metacholine and pilocarpine induce stronger contractions in aganglionic strips than in normal strips. Serotonine has an inhibitory effect in strips from both the proximal and distal segment. Nicotine, lobeline and DMPP do not induce a relaxation in aganglionic muscle strips. All strips contract after histamine, but the contractions are stronger in aganglionic strips. It is concluded that there are no pharmacological arguments and no explanations for spasticity of the distal aganglionic colon and that the type of denervation is certainly different from the type described by Cannon.