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 739 records · Page 41Linked to original sources
PubMed1995

Rigid-body motions of sub-units in DNA: a correlation analysis of a 200 ps molecular dynamics simulation.

A 200 ps molecular dynamics simulation of the B-form double stranded self-complementary octanucleotide d(CTGATCAG) is analyzed in terms of correlated motions using the canonical analysis approach. Each nucleotide is decomposed in three sub-units corresponding to the base, the sugar ring and the backbone respectively. The correlation between the full dynamics of two sub-units was found to decrease as their mutual distance increases. The interpretation of the full dynamics of sub-units as the superimposition of rigid-body motions (translation and orientation) and deformation shows that the main source of correlation is rigid-body motions. Correlation between sub-units deformation is weak and practically vanishes for sub-units belonging to non-adjacent nucleotides. It is also shown that the correlation is much more important for sub-units of the same strand than of opposite strands. We conclude that the internal dynamics of the octanucleotide may be well described by rigid-body motions, the sub-units deformation having only local influence whereas sub-units translation and rotation have repercussion to long distances. The results presented in this study suggest how the number of degrees of freedom may be reduced for simulating long-time dynamics of oligonucleotides.

Computer Simulation↗
PubMed2005

A finite element comparison between the mechanical behaviour of rigid and resilient oral implants with respect to immediate loading.

In this paper, a qualitative comparison between two types of dental implants with respect to their behaviour under immediate loading is presented. This analysis has been carried out using the finite element method. Since micromotions (and not the load) are responsible of the appearance of a fibrous interface avoiding osseointegration, the relative displacement between the bone surface and the implant has been the main variable analyzed at different loading states and for the two implant types here considered. The implants analyzed differ in their mechanical behavior: rigid or resilient. Their main difference lies in the joining between the different pieces that make up the dental system. While in the rigid implant all the pieces are screwed, in the resilient implant a relative displacement between the pieces is allowed, with the additional introduction of a silicone gasket that acts like the periodontal ligament. Both implants were considered with a similar geometry and under two different loading scenarios, one equivalent to the force of chewing applied to a molar and another which corresponds to a premolar. For the resilient implant, a hyperelastic behaviour for the silicone and contact conditions between the different mobile parts of the implant are considered. The displacements of the emerging-body in both designs are also compared with the values obtained by several authors. However, the results show that both implants fulfill the constraint of the immediate loading protocol. The micromotions of the resilient implant are lower to those of the rigid one, favouring therefore a good osseointegration process while keeping the stresses in the implant under admissible maximum values.

Computer Simulation↗
PubMed1991

Effect of educational programs, rigid sharps containers, and universal precautions on reported needlestick injuries in healthcare workers.

OBJECTIVE: To evaluate the effect of infection control programs on reported needlestick injuries in a general hospital. DESIGN: Surveillance of all reported needlestick injuries at the University of Cincinnati Hospital was maintained by the infection control department for five years, from 1985 through 1989. Data on individual workers were collected, tabulated on a monthly basis, and reviewed continually to monitor trends in injuries. During this time, the effects of each of three new infection control programs on reported injuries were evaluated sequentially. SETTING: A 700-bed general hospital that serves as the main teaching hospital of the University of Cincinnati. PARTICIPANTS: All employees of University Hospital who reported to personnel health for management of needlestick injuries. INTERVENTIONS: In 1986, an educational program to prevent injuries was initiated and continued throughout the surveillance period. In 1987, rigid sharps disposal containers were placed in all hospital rooms. In 1988, universal precautions were introduced with an intensive inservice. RESULTS: Surveillance identified 1,602 needlestick injuries (320/year) or 104/1,000/year. After the educational program began, reported injuries increased rather than decreased, and this was attributed to increased reporting. Subsequently, after installation of the new disposal containers, reported injuries returned to the levels seen prior to the educational program, but recapping injuries showed a significant decrease from 63/year to 30, or 20/1,000/year to 10. This decrease was observed in nurses but not in other healthcare workers. After universal precautions were instituted, total injuries increased slightly, but recapping injuries remained at 50% of the levels reported prior to the use of rigid sharps disposal containers. CONCLUSIONS: The three infection control programs failed to produce a major reduction in reported needlestick injuries, except for a decrease in recapping injuries associated with the placement of rigid sharps disposal containers in all patient rooms. These observations indicate that new approaches are needed to reduce needlestick injuries.

Accidents, Occupational↗
PubMed2002

Pressure-release versus rigid reflector for extracorporeal shockwave lithotripsy.

PURPOSE: To evaluate the advantages and disadvantages of using a pressure-release reflector instead of a rigid reflector to concentrate shockwaves for extracorporeal shockwave lithotripsy (SWL). MATERIALS AND METHODS: As in all electrohydraulic lithotripters, shockwaves were generated by electrical breakdown of water between two electrodes, located at the focus (F1) closest to a paraellipsoidal reflector. A pressure-release reflector, made out of polyurethane foam, was constructed and tested on a research lithotripter using kidney stone models. Fragmentation data and pressure measurements were compared with those of a conventional rigid reflector tested on the same device. RESULTS: The weight of stone model fragments remaining after shockwave exposure was less with the pressure-release reflector after screening through a 3.0 x 3.0-mm mesh. The residual fragment weight was less with the rigid reflector using 1.0 x 1.0- and 0.6 x 0.6-mm meshes. CONCLUSION: Pressure-release reflectors may maintain acceptable stone fragmentation while offering improved patient safety and should be considered for SWL.

Equipment Design↗
PubMed2001

Gray matter of the bovine cervical spinal cord is mechanically more rigid and fragile than the white matter.

The gray matter of the cervical spinal cord has been thought to be equally or less rigid than the white matter. Based on this assumption, various studies have been conducted on the changes of stress distributions within the spinal cord under mechanical compression, although the mechanical properties of the white and gray matters had not been fully elucidated. The present study measured the mechanical properties of the white and gray matter of bovine spinal cords. For both the white and gray matter, the stress-strain curves had a nonlinear region, followed by a linear region, and then a region where the stresses plateaued before failure. In the nonlinear region, stress was not significantly different between the gray and white matter samples (strain approximately 0-10%), while stress and Young's modulus in the gray matter was significantly higher than the white matter in the linear part of the curve. The gray matter ruptured at lower strains than the white matter. These findings demonstrated the gray matter is more rigid and fragile than the white matter, and the conventional assumption (i.e., the white matter is more rigid than the gray matter) is not correct. We then applied our data to computer simulations using the finite element method, and confirmed that simulations agreed with actual magnetic resonance imaging findings of the spinal cord under compression. In future computer simulations, including finite element method using our data, changes in stress and strain within the cervical spinal cord under compression would be clarified in more detail, and our findings would also help to elucidate the area which can easily receive histologic damage or which could have hemodynamic disorders under mechanical compression, as well as severity and location of biochemical and molecular biological changes.

Animals↗
PubMed2005

Reduction in mouth opening with semi-rigid cervical collars.

BACKGROUND: Reduced mouth opening may be a major contributing factor to the deterioration in the view obtained at laryngoscopy when a semi-rigid cervical collar is in place. We set out to assess the degree to which mouth opening is restricted by a cervical collar. METHODS: We measured maximal inter-incisor distance in 52 volunteers. It was measured again after application of each of three appropriately sized semi-rigid cervical collars (Stifneck, Miami J, and Philadelphia). RESULTS: Inter-incisor distance was significantly reduced by the application of a cervical collar [No collar 41 (7) mm-mean (SD); Stifneck 26 (8) P<0.0001; Miami J 29 (9) P<0.0001; Philadelphia 29 (9) P<0.0001]. There was a wide and unpredictable variation between subjects in the reduction in mouth opening and a significant proportion had an inter-incisor distance of 20 mm or less (Stifneck, 25%; Miami J, 21%; Philadelphia, 21%). CONCLUSIONS: Application of a semi-rigid cervical collar can significantly reduce mouth opening. This could hinder definitive airway placement. Our results support removing the anterior portion of the collar before attempts at tracheal intubation.

Anthropometry↗
PubMed1996

Comparison of NMR and molecular modeling results for a rigid and a flexible oligosaccharide.

Three-bond heteronuclear coupling constants (3JCH) are extremely useful in describing flexible models for oligosaccharides. We show that antiphase methods for measuring 3JCH in oligosaccharides have limited reliability but that the coupling constants can be reliably measured in natural abundance by quantitative J-correlation methods. Interpretation of 3JCH data for a pentasaccharide (lacto-N-fuco-pentaose 2) from human milk are consistent with a rigid model for the Lewis(a) trisaccharide epitope but for an antigenic tetrasaccharide fragment from the cell wall polysaccharide of viridans streptococci, 3JCH data imply a considerably more flexible model. Nuclear Overhauser effect (NOE) data are reported for a heptasaccharide repeating unit isolated from the cell wall polysaccharide of Streptococcus gordonii 38. The results for a tetrasaccharide fragment are similar to data reported for the same fragment in the cell wall polysaccharide from S.mitis J22. This result implies a similar conformation for the tetrasaccharide fragment in the polysaccharide and in the heptasaccharide and also implies that anisotropy of motion is not significant in the interpretation of the nuclear Overhauser effects in the polysaccharide. Interpretation of the NOE results for the tetrasaccharide fragment, like the 3JCH data, implies a flexible model with three conformations in fast exchange. The results of the two experimental techniques are combined with molecular modeling results including molecular dynamics simulation to provide a clear delineation between flexible and rigid oligosaccharide epitopes. The blood group Lewis(a) trisaccharide antigenic determinant is highly restricted in its motions by steric interactions while the antigenic tetrasaccharide fragment of the S.gordonii 38 heptasaccharide is considerably more mobile. We propose that some branched oligosaccharides are relatively rigid and some are flexible depending on subtle details of the linkages.

Carbohydrate Conformation↗
PubMed1982

Comparison of removable rigid dressings and elastic bandages in preprosthetic management of patients with below-knee amputations.

The purpose of this study was to determine if the removable rigid dressing is more effective in preprosthetic management than the conventional support dressing with elastic bandages. Residual limb circumference, independent application of the dressing, tendency of the dressing to remain secure, development of pressure areas, and presence of pain were evaluated in two groups of below-knee amputees. Subjects were randomly assigned to use either removable rigid dressings or conventional elastic bandages. Residual limb circumference was measured three times a week, and the other variables were measured weekly. The results indicated that the removable rigid dressing is more effective in preprosthetic management than the elastic bandage.

Aged↗
PubMed1988

Interrater reliability of a clinical scale of rigidity.

The purposes of this study were 1) to describe a clinical scale of rigidity and testing procedure for use in patients with Parkinson's disease and 2) to examine the scale's interrater reliability. Twenty subjects (3 women, 17 men; mean age = 64 years, s = 16.3) participated in the study. Criteria for participation were 1) diagnosis of Parkinson's disease, 2) physician-documented rigidity, 3) ability to follow one-step verbal directions, and 4) ability to attain at least 75% of the standard passive-range-of-motion measurements of the elbow, forearm, and wrist of the tested upper extremity. Each of two raters used a standardized set of instructions and test procedures. The degree of rigidity was assessed using a four-point scale ranging from 0 (absent) to 3 (severe). The observed agreement between raters was 16 out of 20 trials. A Cohen's weighted Kappa was used to analyze the data (Kw = .636, p = .20). Factors were identified that may have contributed to the discrepancy between agreement and the agreement beyond chance.

Female↗
PubMed1993

The ischiocavernosus and bulbospongiosus muscles in mammalian penile rigidity.

The role of the perineal muscles in erection physiology is currently controversial. Specifically, confusion persists as to the function, if any, the ischiocavernosus (IC) and bulbospongiosus (BS) muscles possess in nonejaculatory erections. An extensive review of the evidence for and against such an erectile role across five orders of mammalian species indicates that the IC muscles create rigidity by producing suprasystolic intracavernous pressures. The BS muscles, on the other hand, are primarily involved in expelling semen during ejaculation. Beckett and coworkers were the first to demonstrate a clear relationship between IC muscle contractions, suprasystolic intracavernous pressures and rigidity. This Beckett model is used to differentiate an erect phase from a rigid erect phase in the erection cycle. The involvement of these muscles in sleep-related erection physiology is also reviewed. Clinical implications and directions for future research are discussed.

Animals↗
PubMed1998

Alternative techniques in rigid fixation of the craniomaxillofacial skeleton.

Rigid fixation techniques in pediatric craniofacial surgery have enhanced our clinical results by offering greater stabilization and control of bone grafts and osteotomized free segments of the craniofacial skeleton. A potential disadvantage of rigid fixation techniques in the growing craniofacial skeleton includes possible long-term growth restrictions, which have been demonstrated in various animal models. Our goal was to evaluate alternative fixation techniques in the growing craniofacial skeleton of the rabbit to study how altering fixation techniques affects craniofacial development. Eighty New Zealand White rabbits were used in this study. Rabbits were divided into eight groups of 10 each, and seven variant fixation techniques were used to stabilize the frontal bones after bifrontal craniectomies. In all groups except Group 1, the animals underwent a bifrontal craniectomy with orthotopic replacement of the frontal bones. Fixation for each group was as follows: Group 2, wire; Group 3, full microplate; Group 4, suture; Group 5, microplate removal at 4 weeks; Group 6, anterior plate; Group 7, posterior plate; Group 8, soft plate. It was demonstrated that long-term effects on craniofacial development in this animal model are significantly influenced by the type and location of rigid fixation hardware. Significant differences in growth of the craniofacial skeleton for the different fixation groups are presented and discussed.

Animals↗
PubMed2001

Radiographic evaluation of bone formation in the pterygoid region after maxillary distraction with a rigid external distraction (RED) device.

In recent years, distraction osteogenesis has been used to correct skeletal disharmonies in the craniofacial region including the mandible and maxilla. Rigid external distraction has been used successfully to correct severe maxillary skeletal discrepancies. However, the characteristics of the newly formed bone have not been studied. A modified tomogram technique was used to analyze the radiological characteristics of the bone generated after maxillary advancement with rigid external distraction. The newly developed protocol may assist the clinician to evaluate the distracted area and to determine the length of stabilization required after active treatment with rigid external distraction.

Adolescent↗
PubMed2001

Traumatic cranial injury sustained from a fall on the rigid external distraction device.

Distraction osteogenesis has become a popular treatment of congenital maxillocraniofacial anomalies. Many ingenious internal and external devices have been developed and used. The rigid external distraction system based on systems previously used in correction of maxillary retrusion offers postoperative adjustment in two dimensions. Figueroa and Polley reported the use of this device with minimal morbidity in children as young as 5 years of age. They reported no problems with infection, bleeding, pain, loosening of the intraoral splint, dental injury, or wear problems in a series of 14 consecutive cleft patients. Recent modification of the system, rigid external distraction II, has allowed it to be applied to more complex craniofacial deformities that require a LeFort III osteotomy. A review of the neurosurgery and orthopedic literature revealed that halo complications relate primarily to the skull pins. In most cases, these complications can be prevented if the device is carefully applied and monitored. Early recognition and prompt treatment of complications are important. After experience with this system for advancement at the LeFort III level, six patients with various syndromes involving the craniofacial skeleton have undergone LeFort III level distraction osteogenesis with the rigid external distraction device in combination with a planned and stabilized frontosupraorbital advancement. In one of these cases, a 7-year-old child fell on the device after discharge from the hospital and sustained a compound depressed skull fracture that required debridement and repair.

Absorbable Implants↗
PubMed1999

Tear film instability induced by rigid contact lenses.

PURPOSE: To evaluate rigid contact lens-associated epithelial damage, the relationship between the tear film and the ocular surface epithelium was evaluated at the perilimbal area around rigid contact lenses (RCLs). METHODS: Twenty RCL [six polymethylmethacrylate (PMMA) and 14 rigid gas-permeable lens (RGPL)] wearers and 20 non-CL wearers were enrolled in this study. By using a newly developed tear interferometer, the noninvasive tear film break-up time (NIBUT) on the conjunctiva at the 3- and 9-o'clock portions was measured, and its stability evaluated. Fluorescein and sulforhodamine B staining was used to observe ocular-surface epithelial damage, and rose bengal staining was used to evaluate the mucin layer distribution. RESULTS: The conjunctival NIBUT at the 3- or 9-o'clock portions or both was abnormally shortened in 15 (75%) of 20 RCL-wearer eyes. Conjunctival epithelial staining at the 3- or 9-o'clock portion was seen in six (30%) of 20 eyes by using sulforhodamine B, and in four (20%) of 20 eyes by rose bengal; all of these eyes also demonstrated an abnormal tear film breakup. Corneal epithelial damage was seen in two (10%) of 20 RCL-wearer eyes at the 3- or 9-o'clock portions or both, and in both of these cases, conjunctival epithelial damage also was noted. Neither tear-film instability nor epithelial staining was seen in the normal controls. CONCLUSIONS: This study indicates that RCL-induced tear-film instability is associated with damage to the ocular-surface epithelium and mucin layer.

Adult↗
PubMed1983

Cognitive deficit in schizophrenia. Subvocal mediation, rigidity, and complexity parameters.

This study investigated the effects of problem complexity on cognitive performance of 96 schizophrenic and nonpsychiatric inpatients. Subvocal activity (mediation) and three rigidity parameters were examined in relation to performance. The major findings were: a) with increased problem complexity, schizophrenics demonstrated relatively greater difficulty in performance than controls; b) subvocal activity was greater in schizophrenics than controls and was positively related to both the complexity of the problem and the inability to respond correctly; c) motor-cognitive rigidity was higher in schizophrenics and positively correlated with cognitive errors, as well as with the subvocal activity--this was not so in controls, demonstrating the differential role of the rigidity dimension in the two populations.

Adult↗
PubMed1998

The correlation among cavernous pressure, penile rigidity and resistance index.

PURPOSE: We define the precise meaning and diagnostic significance of the resistance index generated by duplex scanning. MATERIALS AND METHODS: In 80 patients penile rigidity was clinically evaluated and a penile duplex scan was performed after intracavernous injection of 10 microg. prostaglandin E1. The intracavernous equilibrium pressure was measured in 34 of these patients. RESULTS: We found a statistically highly significant linear relationship among cavernous pressure, resistance index and penile rigidity (p <0.001). CONCLUSIONS: The resistance index and clinical degree of penile rigidity are 2 expressions of intracavernous pressure. Clinical observation of erection is equivalent to the resistance index in screening for cavernous leakage.

Adult↗
PubMed2002

C1-C2 pedicle screw fixation with rigid cantilever beam construct: case report and technical note.

OBJECTIVE AND IMPORTANCE: Transarticular screw fixation of the C1-C2 complex provides immediate rigid fixation of the unstable spine. The technique is not feasible in a certain proportion of patients because of the position of the vertebral artery or the patient's body habitus. CLINICAL PRESENTATION: The authors describe a rigid screw technique for the surgical treatment of a woman who was excluded as a candidate for C1-C2 transarticular screw fixation. TECHNIQUE: C1-C2 pedicle screw fixation was achieved using a fixed moment arm cantilever beam system. This system provided immediate rigid fixation of the C1-C2 complex in a patient who was not a candidate for transarticular screw fixation. CONCLUSION: This technique is technically more forgiving than posterior transarticular screw fixation and may be applied to a broader spectrum of patients.

Bone Screws↗
PubMed1985

Rigid gas-permeable lenses for extended wear--a 1-year clinical evaluation.

A 1-year evaluation of the feasibility of the use of gas-permeable rigid lenses for extended wear was carried out, using two different materials. Forty subjects were entered into the study. Fifteen were fitted with the Polycon II lens and another 15 with the Boston IV lens. These two groups wore the lenses on a weekly basis for the duration of the study. Two other groups, the controls, were fitted with the same types of lenses as the experimental groups, but wore the lenses on a daily basis. All lenses were made to the Syntex specifications for the Polycon lens and the groups were comparable with regard to age, sex, refractive error, corneal astigmatism, and any pre-existing ocular pathology. All subjects carried out the same care regimen for their lenses and were examined after 24 h, 1 week, 1 month, 3 months, 6 months, and 1 year. Examinations performed at the follow-up visits were to determine any clinically observable effects of lens wear in each patient in all groups. The results of the study suggest that the extended wear of gas-permeable rigid materials is a viable option. However, the results also indicate that extended wear is not without problems, and these need to be studied more fully before the use of gas-permeable rigid lenses for extended wear can be recommended.

Adult↗