Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “RIGIDITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1993

Molecular dynamics simulations and rigid body (TLS) analysis of aspartate carbamoyltransferase: evidence for an uncoupled R state.

In the R form of ATCase complexed with the bisubstrate analogue, N-(phosphonacetyl)-L-aspartate, large temperature factors are reported for the allosteric domains of the regulatory chains. We studied the conformational flexibility of the holoenzyme with molecular dynamics simulations and rigid body (TLS) analysis. The results of the molecular dynamics simulations suggest that, although local atomic fluctuations account for the temperature factors of the catalytic and zinc domains, they do not account for the large temperature factors of the allosteric regions. However, the temperature factors of the allosteric domains can be satisfactorily analyzed using a rigid body model. The simulations and rigid body analysis support the idea that the allosteric regions are mechanically uncoupled from the rest of the enzyme in the PALA structure. Implications of this uncoupling for allosteric regulation are discussed.

Allosteric Site↗
PubMed1996

Effects of steric bulk and conformational rigidity on fatty acid omega hydroxylation by a cytochrome P450 4A1 fusion protein.

The action of cytochrome P450 4A1 (CYP4A1) on fatty acid substrates is characterized by a pronounced regioselectivity for omega-hydroxylation. To elucidate the chemical basis of this specificity we probed the active site of a CYP4A1 fusion protein (f4A1) with bulky and/ or rigid analogs of lauric acid, the optimum natural substrate for f4A1 and CYP4A1. f4A1 efficiently omega-hydroxylates lauric acid, epoxidizes 11-dodecenoic acid, and oxidizes 11-dodecynoic acid to 1,12-dodecanedioic acid. Medium length fatty acids having omega-terminal groups as large as t-butyl or m-tolyloxy bind tightly to f4A1 as Type I ligands and are efficiently hydroxylated on their methyl termini. omega-Phenylnonanoic acid also induces a Type I binding spectrum (Ks = 0.77 microM) but fails to undergo hydroxylation and strongly inhibits lauric acid hydroxylation by f4A1. Slightly shorter acids such as omega-phenyloctanoic acid, naproxen, and ibuprofen also strongly inhibit lauric acid hydroxylation but do not induce a Type I spectrum and do not undergo hydroxylation. Like 10-methoxydecanoic acid, the rigid and rod-like 4'-methoxy-4-biphenylcarboxylic acid is O-demethylated by f4A1, which also omega-hydroxylates m- and p-heptyloxybenzoic acids but not m- or p-amyloxyhydrocinnamic acids. The histamine antagonist cimetidine and the peroxisome proliferator perfluorodecanoic acid are both potent inhibitors of f4A1. Thus the active site of f4A1 is quite tolerant of steric bulk and rigidity around the heme region and the polar group recognition site, but perhaps less so in the midchain region. Although CYP4A enzymes are not usually regarded as "drug metabolizing P450s," the fact that commonly used therapeutic agents strongly inhibit lauric acid omega-hydroxylation by f4A1 as well as liver microsomes from clofibrate-induced rats suggests these and related agents could potentially interfere with the contribution of CYP4A enzymes to the metabolism of endogenous lipids.

Allosteric Site↗
PubMed1998

Family rigidity, adolescent problem-solving deficits, and suicidal ideation: a mediational model.

Family rigidity and adolescent problem-solving deficits have each been linked to adolescent suicidal behaviors. The objective of the present study was to evaluate the hypothesis that family rigidity has primarily an indirect effect on adolescent suicidal ideation through its effect on adolescent problem-solving deficits. College students and their parents completed the Family Adaptability and Cohesion Evaluation Scale II. Students also completed the Problem-Solving Inventory and the Adult Suicidal ideation Questionnaire. Structural equation models confirmed that family rigidity has an indirect effect on adolescent suicidal ideation through its effect on adolescent problem-solving deficits. Directions for treatment efforts are discussed.

Adaptation, Psychological↗
PubMed2001

Forces between a Rigid Probe Particle and a Liquid Interface.

The effect of disjoining pressure between a rigid spherical probe particle (attached to an AFM cantilever) and a liquid interface (e.g., oil/water or air/water) is treated in an analytic manner to describe the total force F exerted on the probe as a function of the distance X of the probe from the rigid substrate (AFM stage) on which the liquid interface resides. Two cases (i) a flat interface under gravity and (ii) a drop whose size is sufficiently small that gravity can be neglected have been examined. A simple numerical algorithm is given for computing F(X) (the AFM observable) from a given form for the disjoining pressure. Numerical results are displayed for electrostatic probe/interface interactions which reveal the linear compliance regime experimentally observed in AFM experiments on these systems. The slope of the linear compliance regime is shown to be a function of the properties of the interface (capillary length, particle radius, drop size, contact angle of drop on rigid substrate etc.). Copyright 2001 Academic Press.

Journal Article↗
PubMed2002

Estimation of torsional rigidity in primate long bones.

Comparative studies of long bone biomechanics in primates frequently use the polar moment of inertia (J ) as a variable reflecting overall mechanical rigidity, average bending rigidity, or resistance to torsional shear stresses. While the use of this variable for characterizing the first two properties is appropriate, it is potentially a highly misleading measure of torsional resistance. Errors result from violations of assumptions required for the use of the polar moment of inertia; in particular, the predictive utility of J diminishes with departures from axial symmetry (i.e., a cylindrical cross-sectional shape). The magnitude of these errors is estimated both theoretically and experimentally. It is argued that the use of the polar moment of inertia for estimating long bone torsional rigidity should be restricted to samples of relatively invariant and/or cylindrical geometry. Alternative measures for torsional resistance are evaluated and reviewed.

Adaptation, Physiological↗
PubMed2005

Adaptive subdivision for hierarchical non-rigid registration of multi-modal images using mutual information.

In this paper we present an enhanced method for non-rigid registration of volumetric multi-modal images using Mutual Information (MI). Based on a hierarchical subdivision scheme, the non-rigid matching problem is decomposed into numerous rigid registrations of sub-images of decreasing size. A thorough investigation revealed limitations of this approach, caused by a peculiar behavior of MI when applied to regions covering only a limited number of image pixels. We examine and explain the loss of MI's statistical consistency along the hierarchical subdivision. We also propose to use information theoretical measures to identify the problematic regions in order to overcome the MI drawbacks. This does not only improve the accuracy and robustness of the registration, but also can be used as a very efficient stopping criterion for the further subdivision of nodes in the hierarchy, which drastically reduces the computational costs of the entire registration procedure.

Algorithms↗
PubMed1996

Haloperidol-increased muscle tone in rats as a model of parkinsonian rigidity.

The aim of the present study was to find out whether haloperidol-induced rigidity was similar to that seen in parkinsonism. Simultaneous measurements of the muscle resistance (mechanomyogram, MMG) of the hind foot to passive flexion and extension in the ankle joint, as well as determination of the electromyographic (EMG) activity of the gastrocnemius and tibialis anterior muscles of rats were carried out. Haloperidol was injected in doses of 0.5-10 mg/kg 1 h before the start of measurements. Haloperidol increased, in a dose-dependent manner, the muscle resistance of the rat's hind leg to passive movements. Muscle rigidity was accompanied with an increase resting, as well as in the stretch-induced long-latency EMG activity (in which supraspinal reflexes are most probably involved) in both those muscles, whereas the short-latency EMG activity (first large bursts of EMG activity, beginning ca. 9 ms after the start of a movement, probably of a spinal origin) was significantly decreased. The obtained results suggest that the haloperidol-increased MMG/EMG activity might be a good model of parkinsonian rigidity.

Animals↗
PubMed1980

The management of amputations of the leg using a new rigid foam plaster for prosthetic fitting.

This paper describes the use of a rigid polyurethane foam to construct a stump socket for immediate or early prosthetic fitting in 15 patients with amputation through the leg. The foam plaster is poured into a prepared cotton sleeve, with a zip incorporated, and rolled out to a layer 4 mm thick. The filled sleeve is put around the stump and the zip closed, moulding the sleeve firmly to the stump. The closed sleeve hardens into a rigid polyurethane shell within 20 min. Aferwards the skeletal prosthetic components are fixed with the same rigid foam. The polyurethane foam socket is quickly and cleanly prepared, only one third of the weight of a plaster of Paris cast and is easily removed by means of the zip, allowing access to the stump.

Aged↗
PubMed1981

Rigid spine syndrome: clinical and histological problems.

A case is described with the characteristic clinical features of rigid spine syndrome: childhood onset in a male, very slowly progressive weakness and muscle atrophy, limitation of neck and trunk flexion, joint contractures, normal intelligence, no clear family history, increased serum CPK levels and myopathic patterns in EMG and muscle biopsy specimens. Myopathic patterns with various histological changes in muscle biopsy specimens were seen in all eight reported cases of the rigid spine syndrome, but there are no characteristic histological findings in the rigid spine syndrome.

Adolescent↗
PubMed1988

Experimental analysis of effects of pin pretensioning on external fixator rigidity.

The effects of same-fragment pin pretensioning on the rigidity of a simple fixator system were investigated. An external fixator device constructed to apply same-fragment pin pretensioning of a defined amount was applied to a bone model made of pedilen cylinders. System rigidity was tested for varying degrees of pin pretensioning in axial compression and AP bending. Pin pretensioning, bringing transfixing pins together, tended to weaken the system in both modalities tested. Tensioning by bringing the pins apart increased the rigidity of the system in AP bending and axial compression.

Biomechanical Phenomena↗
PubMed1996

Rigid osteosynthesis decreases the late complication rate after femoral neck fracture. The influence of three different osteosynthesis devices evaluated in 369 patients.

The influence of three different fixation devices on late healing complications after femoral neck fractures was studied in a large patient group from three different hospitals. Except for the choice of device, which was unique to each hospital, all other factors having a potential influence on the late outcome, such as sex and age of the patients, initial degree of fracture dislocation and quality of surgical reduction were similar among the three groups. Within a 2-year observation period the incidence of late segmental collapses (14%-19%) was not related to choice of device, but a higher number of non-unions (27%-30%) occurred after adaptive non-rigid methods using screws (von Bahr) or a flanged nail (Rydell) than after a more rigid osteosynthesis (8%, Deyerle). Using such a rigid fixation, the complication rate could be reduced by one-third and the need for revision surgery halved. A device providing stable fixation should be preferred for treatment of femoral neck fractures in the elderly to prevent the healing complications related to insufficient stabilization.

Adult↗
PubMed1996

Factors in the cycle of violence: gender rigidity and emotional constriction.

A sample of 595 men were administered self-report assessments of childhood sexual and physical abuse, perpetration history, gender rigidity and emotional constriction. Including noncontact forms of sexual abuse, 11% of the men reported sexual abuse alone, 17% reported physical abuse alone, and 17% reported both sexual and physical abuse. Of the 257 men in the sample who reported some form of childhood abuse, 38% reported some form of perpetration themselves, either sexual or physical; of the 126 perpetrators, 70% reported having been abused in childhood. Thus, most perpetrators were abused, but most abused men did not perpetrate. Both sexually and physically abused men who perpetrated manifested significantly more gender rigidity and emotional constriction than abused nonperpetrators. Men who reported abuse but not perpetration demonstrated significantly less gender rigidity, less homophobia and less emotional constriction than nonabused men.

Adult↗
PubMed1985

General anaesthesia for Nd:YAG laser resection of obstructing endobronchial tumours using the rigid bronchoscope.

Provision of general anaesthesia for patients undergoing Nd:YAG laser resection of obstructing endobronchial tumours using the rigid bronchoscope presents unique problems for the anaesthesiologist. We studied 15 patients who underwent 20 of these procedures under general anaesthesia. Patients were anaesthetized and ventilated with either potent inhalation agents via the side arm of the ventilating bronchoscope (Group I: N = 8), or with intravenous agents and the Sanders jet injector attached to the rigid bronchoscope (Group II: N = 12). Patients were paralyzed and ventilation was controlled. The inspired gas mixture was nitrogen and oxygen, and the FIO2 was decreased to 0.3-0.4 during periods of resection. Group I patients had significantly higher peak pCO2's than Group II (8.3 kPa (62 mmHg) vs. 5.6 kPa (44 mmHg); lowest recorded pO2's were comparable and similar to pre-induction values. Both groups exhibited wide blood pressure fluctuations. Heart rates remained within 15 per cent of pre-induction levels. There were no intraoperative deaths, and no airway fires, massive haemorrhages or pneumothoraces. We conclude that these procedures can be undertaken with the use of general anaesthesia and the rigid bronchoscope, but that patients may encounter potentially serious respiratory or haemodynamic instability during the procedure.

Aged↗
PubMed2004

Rigidity and spontaneous curvature of lipidic monolayers in the presence of trehalose: a measurement in the DOPE inverted hexagonal phase.

Trehalose is a sugar which plays an important protectant role in organisms against damage due to dehydration. To explore the basic molecular mechanism which governs the protective function exerted on lipid membranes, X-ray diffraction and osmotic stress experiments have been performed on L: -alpha-dioleoyl-phosphatidyl-ethanolamine (DOPE) in trehalose solutions of different concentrations. In pure water, DOPE forms an inverted hexagonal (H(II)) phase; in sugar solutions, a strong dehydration, which induces a large reduction of the H(II) lattice parameter, has been detected, but nevertheless no phase transitions occur. Structural data, directly obtained from reconstructed electron density maps, show that the bending of the lipid monolayer induced by the sugar is coupled to changes in the DOPE molecular shape. By osmotic stress, the work required to dehydrate the monolayer has been obtained and the overall free energy described as a function of trehalose concentration. Three results should be stressed: (1) dehydration experiments performed in the presence of sugar demonstrate that the protective effect cannot be purely osmotic; (2) the pivotal surface, that location on the molecule whose area is invariant upon isothermal bending, has been analyzed by two different methods: the approach by Rand and co-workers and the approach by Templer and co-workers; in both cases its presence along the DOPE molecule has been revealed and its position estimated; (3) the spontaneous radius of curvature and the rigidity constant of the lipid monolayer, measured at the pivotal plane, changes from 3.06 nm (in pure water) to 2.82 nm (in 1.4 M trehalose), and from 0.55 x 10(-19) to 0.74 x 10(-19) J, respectively. We assume that these modifications are related to direct interactions between trehalose and DOPE that alter the interface geometry, reducing the repulsion between the polar heads. However, the increased bending rigidity also accounts for the changes of the property of the aqueous compartment, reflecting the rigidity and stiffness of the sugar matrix around and inside the lipid phase.

Lipid Bilayers↗
PubMed2001

Vardenafil increases penile rigidity and tumescence in erectile dysfunction patients: a RigiScan and pharmacokinetic study.

The pharmacodynamic effect on penile rigidity and tumescence and the pharmacokinetic properties of single oral doses of 10 and 20 mg vardenafil, a new PDE5-inhibitor, were investigated in 21 erectile dysfunction patients. Patients were evaluated with RigiScan on three occasions in a randomized, placebo-controlled, double-blind crossover fashion, while receiving visual sexual stimulation. Relative to placebo, a single dose of 10 mg vardenafil led to a mean increase in the duration of >60% penile rigidity of 24.4 min (95% CI: 7.4 to 41.3) at the base and of 24.8 min (8.5 to 41.1) at the tip. For the 20-mg dose, the increase in duration of > 60% penile rigidity relative to placebo was 37.2 min (20.2 to 54.1) at the base and 28.7 min (12.7 to 44.7) at the tip. Single doses of 10 and 20 mg vardenafil led to a rapid rise in the plasma concentrations of vardenafil, with a median tmax of 0.9 h and 0.7 h and a geometric mean Cmax of 9.1 microg/l (geometric SD = 1.63) and 20.9 microg/l (geometric SD = 1.83), respectively. In the post-absorptive phase, the concentrations declined with an average terminal t 1/2 of 4.2 h (geometric SD = 1.27) and 3.9 h (geometric SD = 1.31). The systemic exposure of vardenafil expressed as AUC normalized for dose and body weight was dose-proportional (associated 90% CI: -4 to 30%) as well as Cmax (associated 90% CI: -12 to 33%). The treatments were well tolerated. There was a small, clinically irrelevant reduction in blood pressure with a small compensatory rise in heart rate. There were no electrocardiographic effects or relevant changes of the safety laboratory screens. The observed pro-erectile properties, pharmacokinetic characteristics and safety profile make vardenafil a suitable candidate for further evaluation in the treatment of erectile dysfunction.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2003

Tracheobronchial amyloidosis treated with rigid bronchoscopy and stenting.

Tracheobronchial amyloidosis (TBA) is an uncommon disease that can cause airway obstruction. We present a case of TBA in a 20-year-old man that was treated successfully with rigid bronchoscopy and stenting. The patient presented with progressive dyspnea despite having had a tracheostomy fashioned at another institution. Airway obstruction secondary to TBA was found distal to the tracheostomy. The amyloid protein subtype was AA, which is uncommon and is seldom of clinical significance in the respiratory tract. The patient underwent rigid bronchoscopy to remove the amyloid protein causing the airway obstruction. A Dumon silicone stent was then inserted to alleviate the obstruction. Thereafter, he recovered well and was discharged without a tracheostomy. This report shows that in patients with TBA causing airway obstruction, excellent results can be obtained with rigid bronchoscopy and stenting of the obstructing lesion.

Adult↗
PubMed2003

Non-rigid immobilisation of odontoid fractures.

Despite various reports on the management of odontoid fractures, there is no consensus on the subject, and the appropriate treatment still remains controversial. While untreated fractures or fractures treated only with a cervical orthosis seem to have the highest rate of non-union, the need for rigid external stabilisation has never been substantiated. In a retrospective analysis we reviewed 26 patients with acute type II and III fractures of the odontoid, treated with a cervical orthosis only. Study inclusion was limited to fractures that had a fracture gap of less than 2 mm, an initial antero-posterior displacement of less than 5 mm and angulation of less than 11 degrees, less than 2 mm displacement on lateral flexion/extension views, and were without neurological deficits. These fractures were defined as stable. There were 19 (73.1%) type II and 7 (26.9%) type III fractures; in 10 (38.5%) of these fractures the odontoid was displaced and/or angulated. The overall complication rate was 11.4% ( n=3). One patient suffered from pulmonary embolism, in two patients (7.7%) with initially minimally displaced fractures, secondary internal stabilisation had to be performed because of persistent instability. In 20 (77%) of the remaining fractures healing was uneventful. In 4 nondisplaced fractures (15%) fibrous union was documented. Three of these patients were over 65 years old. The overall fusion rate was 73.7% for type II and 85.7% for type III fractures. At follow-up 39% of the patients were free of symptoms; however, the clinical outcome did not correlate with the radiological findings. According to our findings, stable type II and type III fractures of the odontoid can be successfully treated with non-rigid immobilisation, even if they are displaced. A thorough assessment of the stability of the odontoid with lateral flexion/extension views or dynamic fluoroscopy is recommended to evaluate the appropriate treatment. Non-rigid immobilisation may be an option in selected cases with stable injuries.

Adolescent↗
PubMed2006

Combined anterior and posterior instrumentation in severe and rigid idiopathic scoliosis.

A prospective clinical and radiographic evaluation of 33 consecutive patients with severe and rigid idiopathic scoliosis (average Cobb angle 93 degrees, flexibility on bending films 23%) were treated with combined anterior and posterior instrumentation with a minimum follow-up of 2 years. All patients underwent anterior release and VDS-Zielke Instrumentation of the primary curve. In highly rigid scoliosis, this was preceded by a posterior release. Finally, posterior correction and fusion with a multiple hook and pedicle screw construct was performed. Thirty patients were operated in one stage, three patients in two stages. Preoperative curves ranged from 80 to 122 degrees Cobb angle. Frontal plane correction of the primary curve averaged 67% with an average loss of correction of 2 degrees . The apical vertebral rotation of the primary curve was corrected by 49%. In all but three patients, sagittal alignment was restored. There were no neurological complications, deep wound infections or pseudarthrosis. Combined anterior and posterior instrumentation is safe and enables an effective three-dimensional curve correction in severe and rigid idiopathic scoliosis.

Adolescent↗