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PubMed2004

Electrostatic contribution to twist rigidity of DNA.

The electrostatic contribution to the twist rigidity of DNA is studied, and it is shown that the Coulomb self-energy of the double-helical sugar-phosphate backbone makes a considerable contribution-the electrostatic twist rigidity of DNA is found to be C(elec) approximately 5 nm, which makes up about 7% of its total twist rigidity ( C(DNA) approximately 75 nm). The electrostatic twist rigidity is found, however, to depend only weakly on the salt concentration, because of a competition between two different screening mechanisms: (1) Debye screening by the salt ions in the bulk, and (2) structural screening by the periodic charge distribution along the backbone of the helical polyelectrolyte. It is found that, depending on the parameters, the electrostatic contribution to the twist rigidity could stabilize or destabilize the structure of a helical polyelectrolyte.

Computer Simulation↗
PubMed1996

Molecular rigid-body displacements in a tetragonal lysozyme crystal confirmed by X-ray diffuse scattering.

X-ray diffuse scattering from protein crystals is, at the moment, the only available experimental process to be directly sensitive to long-range correlations between protein-atom displacements. It is shown here that calculations based on independent rigid-body displacements of individual molecules yield a description in good agreement with the experimental diffuse-scattering pattern displayed by tetragonal crystals of hen egg-white lysozyme (HEWL) In particular, it appears that molecular rigid-body translations and rigid- body rotations appear roughly in the same proportion as the average atomic mean-square positional fluctuations. The crystallographic temperature-factor analysis by TLS (translation/libration/screw) refinement, performed by Sternberg, Grace & Phillips [Sternberg, Grace, & Phillips (1979). J. Mol. Biol. 130, 231-253], is then confirmed and completed by a quantitative estimation of the molecular rigid-body translation contributions. The major contribution of molecular rigid- body displacements to the average atomic mean-square positional fluctuations, contradicts a previous analysis of the tetragonal HEWL diffuse-scattering data by Clarage, Clarage, Phillips, Sweet & Caspar [Clarage, Clarage, Phillips, Sweet & Caspar (1992). Proteins Struct. Funct. Genet. 12, 145-157] which concluded that short-range correlations dominate. The origin of these opposite conclusions mostly lies in the different hypotheses made to model diffuse scattering, underlying the limits of the 'homogeneous disorder' model.

Journal Article↗
PubMed1998

Predicting error in rigid-body point-based registration.

Guidance systems designed for neurosurgery, hip surgery, and spine surgery, and for approaches to other anatomy that is relatively rigid can use rigid-body transformations to accomplish image registration. These systems often rely on point-based registration to determine the transformation, and many such systems use attached fiducial markers to establish accurate fiducial points for the registration, the points being established by some fiducial localization process. Accuracy is important to these systems, as is knowledge of the level of that accuracy. An advantage of marker-based systems, particularly those in which the markers are bone-implanted, is that registration error depends only on the fiducial localization error (FLE) and is thus to a large extent independent of the particular object being registered. Thus, it should be possible to predict the clinical accuracy of marker-based systems on the basis of experimental measurements made with phantoms or previous patients. This paper presents two new expressions for estimating registration accuracy of such systems and points out a danger in using a traditional measure of registration accuracy. The new expressions represent fundamental theoretical results with regard to the relationship between localization error and registration error in rigid-body, point-based registration. Rigid-body, point-based registration is achieved by finding the rigid transformation that minimizes "fiducial registration error" (FRE), which is the root mean square distance between homologous fiducials after registration. Closed form solutions have been known since 1966. The expected value (FRE2) depends on the number N of fiducials and expected squared value of FLE, (FLE-2, but in 1979 it was shown that (FRE2) is approximately independent of the fiducial configuration C. The importance of this surprising result seems not yet to have been appreciated by the registration community: Poor registrations caused by poor fiducial configurations may appear to be good due to a small FRE value. A more critical and direct measure of registration error is the "target registration error" (TRE), which is the distance between homologous points other than the centroids of fiducials. Efforts to characterize its behavior have been made since 1989. Published numerical simulations have shown that (TRE2) is roughly proportional to (FLE2)/N and, unlike (FRE2), does depend in some way on C. Thus, FRE, which is often used as feedback to the surgeon using a point-based guidance system, is in fact an unreliable indicator of registration-accuracy. In this work we derive approximate expressions for (TRE2), and for the expected squared alignment error of an individual fiducial. We validate both approximations through numerical simulations. The former expression can be used to provide reliable feedback to the surgeon during surgery and to guide the placement of markers before surgery, or at least to warn the surgeon of potentially dangerous fiducial placements; the latter expression leads to a surprising conclusion: Expected registration accuracy (TRE) is worst near the fiducials that are most closely aligned! This revelation should be of particular concern to surgeons who may at present be relying on fiducial alignment as an indicator of the accuracy of their point-based guidance systems.

Humans↗
PubMedDate not supplied

Fracturing rigid materials.

We propose a novel approach to fracturing (and denting) brittle materials. To avoid the computational burden imposed by the stringent time step restrictions of explicit methods or with solving nonlinear systems of equations for implicit methods, we treat the material as a fully rigid body in the limit of infinite stiffness. In addition to a triangulated surface mesh and level set volume for collisions, each rigid body is outfitted with a tetrahedral mesh upon which finite element analysis can be carried out to provide a stress map for fracture criteria. We demonstrate that the commonly used stress criteria can lead to arbitrary fracture (especially for stiff materials) and instead propose the notion of a time averaged stress directly into the FEM analysis. When objects fracture, the virtual node algorithm provides new triangle and tetrahedral meshes in a straightforward and robust fashion. Although each new rigid body can be rasterized to obtain a new level set, small shards can be difficult to accurately resolve. Therefore, we propose a novel collision handling technique for treating both rigid bodies and rigid body thin shells represented by only a triangle mesh.

Compressive Strength↗
PubMed2004

Quantitative assessment of the transport of elastic and rigid vesicle components and a model drug from these vesicle formulations into human skin in vivo.

The aim of this study was to quantitatively assess the distribution profiles of elastic and rigid vesicle material in human skin in vivo. Furthermore, the distribution profiles of the model drug ketorolac applied in these vesicle formulations was investigated. A deuterium-labelled phospholipid was incorporated into these vesicles to serve as a marker for the vesicle material. The vesicles were loaded with ketorolac at saturated concentrations. Vesicle solutions were applied non-occlusively onto the skin and the treated site was sequentially tape-stripped. Tape-strips were analyzed for vesicle material using attenuated total reflectance-Fourier transform infrared spectroscopy and for ketorolac by extraction of the tape-strips followed by high pressure liquid chromatography. Distribution profiles in the stratum corneum (SC) were obtained for the elastic and rigid vesicle material and for the ketorolac. These profiles have suggested that elastic vesicle material can rapidly enter the deeper layers of the SC and can reach almost the SC-viable epidermal junction. Rigid vesicle material, however, did not penetrate deep into the SC. Furthermore, the elastic vesicles were better than the rigid vesicles in the enhancement of ketorolac transport into human SC. The distribution profile of ketorolac in the deeper SC layers was, however, different from that of the vesicle material. This suggests that once the elastic vesicles partition into the SC, the ketorolac is released from the vesicles. The elastic vesicles are superior to the rigid vesicles both in terms of vesicular transport into the SC and in terms of therapeutic potential as a skin delivery vehicle.

Administration, Cutaneous↗
PubMed1990

Validation of a non-invasive device to measure intracavernous pressure as an index of penile rigidity.

Many authors agree with the importance of developing devices to measure penile rigidity. The devices that have been developed over recent years have defined penile rigidity in terms of stiffness. Penile stiffness, however, is believed to result from an increase in intracavernous pressure. The device presented here was therefore designed to estimate intracavernous pressure, rather than penile stiffness, as an index of penile rigidity. Validation of the penile cuff device was achieved by simultaneously recording penile cuff pressure and intracavernous pressure on patients undergoing artificial erections. The results showed a linear relationship and highly positive correlation coefficients between the 2 measures. The results demonstrate that the penile cuff may be used to estimate intracavernous pressure as an index of penile rigidity. The findings are discussed in terms of the possible applications of the cuff as a clinical tool to measure both penile tumescence and penile rigidity.

Adult↗
PubMed1990

Morbidity following cystoscopy: comparison of flexible and rigid techniques.

Recent reports on the value of local anaesthetic flexible cystoscopy have emphasised excellent tolerance and preference for the technique over general anaesthetic rigid cystoscopy. However, no study has yet compared the post-operative morbidity rates of these procedures. Tolerance, preference and post-operative symptoms in 100 patients undergoing local anaesthetic flexible cystoscopy were compared with those in 100 patients undergoing general anaesthetic rigid cystoscopy. On initial questioning, 89% of patients found flexible cystoscopy painless and 92% expressed a preference for the same procedure on a future occasion; 98 patients who underwent flexible cystoscopy and 87 who underwent rigid cystoscopy returned a questionnaire on symptoms 1 week after the procedure. The incidence of post-operative symptoms was 33% following flexible cystoscopy and 76% following rigid cystoscopy. Patients in both groups who were undergoing check cystoscopy had a lower incidence of morbidity than those undergoing cystoscopy for other reasons. The results suggest that flexible cystoscopy was well tolerated and preferred by most patients. The morbidity associated with the procedure was also significantly less than that associated with rigid cystoscopy under general anaesthesia.

Adolescent↗
PubMed2005

Using an extended kalman filter for rigid body pose estimation.

Rigid body pose is commonly represented as the rigid body transformation from one (often reference) pose to another This is usually computed for each frame of data without any assumptions or restrictions on the temporal change of the pose. The most common algorithm was proposed by Söderkvist and Wedin (1993, "Determining the Movements of the Skeleton Using Well-configured Markers," J. Biomech., 26, pp. 1473-1477), and implies the assumption that measurement errors are isotropic and homogenous. This paper describes an alternative method based on a state space formulation and the application of an extended Kalman filter (EKF). State space models are formulated, which describe the kinematics of the rigid body. The state vector consists of six generalized coordinates (corresponding to the 6 degrees of freedom), and their first time derivatives. The state space models have linear dynamics, while the measurement function is a non-linear relation between the state vector and the observations (marker positions). An analytical expression for the linearized measurement function is derived. Tracking the rigid body motion using an EKF enables the use of a priori information on the measurement noise and type of motion to tune the filter. The EKF is time variant, which allows for a natural way of handling temporarily missing marker data. State updates are based on all the information available at each time step, even when data from fewer than three markers are available. Comparison with the method of Söderkvist and Wedin on simulated data showed a considerable improvement in accuracy with the proposed EKF method when marker data was temporarily missing. The proposed method offers an improvement in accuracy of rigid body pose estimation by incorporating knowledge of the characteristics of the movement and the measurement errors. Analytical expressions for the linearized system equations are provided, which eliminate the need for approximate discrete differentiation and which facilitate a fast implementation.

Algorithms↗
PubMed2000

Increased polymorphonuclear leucocyte rigidity in HIV infected individuals.

AIM: Individuals with human immunodeficiency virus (HIV) infection were evaluated for evidence of abnormal polymorphonuclear leucocyte (PMN) rigidity, which can alter capillary blood flow. METHODS: The transit time of individual PMN through 8 microm pores in a cell transit analyser was used as a measure of cell rigidity. PMN transit time was compared between HIV infected individuals (n=45) with and without CMV retinitis and HIV negative controls (n=17). RESULTS: Transit times were longer for PMN from HIV infected individuals than for PMN from controls (p<0.001). PMN from HIV infected individuals with CMV retinitis (n=13) had longer transit times than PMN from those without CMV retinitis (n=32, p<0.001). Transit times were longer in HIV infected individuals with lower CD4+ T lymphocyte counts (p<0.001). Regression analysis indicated that the relation between transit times and the presence of CMV retinitis could not be explained solely on the basis of low CD4+ T lymphocytes. In HIV infected individuals, mean transit time was not correlated with age, blood pressure, or serum creatinine, cholesterol, or triglycerides. CONCLUSIONS: HIV infected individuals appear to have increased PMN rigidity, a cellular change that might be involved in the pathogenesis of HIV related retinal microvasculopathy. PMN rigidity appears to be related to severity of immune dysfunction. PMN rigidity may remain high in patients with CMV retinitis after elevations of CD4+ T lymphocyte counts that result from potent antiretroviral therapy.

Adult↗
PubMed1993

Diagnostic rigid and flexible oesophagoscopy in carcinoma of the oesophagus: a comparison.

BACKGROUND: Flexible oesophagoscopy is regarded as superior to rigid oesophagoscopy on the basis of perforation rates as an end point. This advantage may be more apparent than real because no comparison has been made in a diagnostic setting in patients with carcinoma of the oesophagus with both perforation rate and diagnostic efficacy as indices. METHODS: A retrospective analysis was carried out on data on 336 diagnostic oesophagoscopies in patients with carcinoma of the oesophagus, comparing rigid with flexible oesophagoscopy. RESULTS: Both rigid and flexible oesophagoscopies were performed without perforation when they were used for diagnosis only. Rigid biopsy achieved a diagnostic success rate of 99.3%, compared with 80.5% for flexible oesophagoscopy. CONCLUSIONS: Diagnostic oesophagoscopy can be achieved without perforation with either instrument, but the chance of diagnosing carcinoma was significantly greater with the rigid instrument.

Biopsy↗
PubMed1996

Comparison of rigid and flexible esophagoscopy in the diagnosis of esophageal disease: diagnostic accuracy, complications, and cost.

Rigid esophagoscopy has been used by otolaryngologists for evaluation of the esophagus for over 100 years. Few studies have examined the diagnostic accuracy of rigid esophagoscopy in patients with carcinoma of the head and neck. The goal of our study was to compare the diagnostic accuracy, complication rate, and costs of rigid esophagoscopy and flexible fiber-optic endoscopy in the evaluation of the esophagus in patients with head and neck carcinoma. We retrospectively reviewed the records of 195 patients with head and neck carcinoma who underwent both rigid esophagoscopy and flexible fiber-optic endoscopy within a 6-month period. We discovered 10 cases with discordant findings, of which 5 (50%) were esophageal carcinoma. The estimated cost was less for flexible endoscopy. No complications were reported in either procedure. Our study suggests that flexible fiber-optic endoscopy should replace rigid esophagoscopy in the evaluation of the esophagus in patients with head and neck carcinoma.

Cost-Benefit Analysis↗
PubMed2006

Aquatic turning performance of painted turtles (Chrysemys picta) and functional consequences of a rigid body design.

The ability to capture prey and avoid predation in aquatic habitats depends strongly on the ability to perform unsteady maneuvers (e.g. turns), which itself depends strongly on body flexibility. Two previous studies of turning performance in rigid-bodied taxa have found either high maneuverability or high agility, but not both. However, examinations of aquatic turning performance in rigid-bodied animals have had limited taxonomic scope and, as such, the effects of many body shapes and designs on aquatic maneuverability and agility have yet to be examined. Turtles represent the oldest extant lineage of rigid-bodied vertebrates and the only aquatic rigid-bodied tetrapods. We evaluated the aquatic turning performance of painted turtles, Chrysemys picta (Schneider, 1783) using the minimum length-specific radius of the turning path (R/L) and the average turning rate (omega(avg)) as measures of maneuverability and agility, respectively. We filmed turtles conducting forward and backward turns in an aquatic arena. Each type of turn was executed using a different pattern of limb movements. During forward turns, turtles consistently protracted the inboard forelimb and held it stationary into the flow, while continuing to move the outboard forelimb and both hindlimbs as in rectilinear swimming. The limb movements of backward turns were more complex than those of forward turns, but involved near simultaneous retraction and protraction of contralateral fore- and hindlimbs, respectively. Forward turns had a minimum R/L of 0.0018 (the second single lowest value reported from any animal) and a maximum omega(avg) of 247.1 degrees. Values of R/L for backward turns (0.0091-0.0950 L) were much less variable than that of forward turns (0.0018-1.0442 L). The maneuverability of turtles is similar to that recorded previously for rigid-bodied boxfish. However, several morphological features of turtles (e.g. shell morphology and limb position) appear to increase agility relative to the body design of boxfish.

Animals↗
PubMed2005

Molecular dynamics simulation of a high-affinity antibody-protein complex: the binding site is a mosaic of locally flexible and preorganized rigid regions.

One nanosecond molecular dynamic (MD) simulation of anti-hen egg white lysozyme (HEL) antibody HyHEL63 (HH63) complexed with HEL reveals rigid and flexible regions of the HH63 binding site. Fifty conformations, extracted from the MD trajectory at regular time intervals were superimposed on HH63-HEL X-ray crystal structure, and the root mean squared deviations (RMSDs) and deviations in Calpha atom positions between the X-ray structure and the MD conformer were measured. Residue positions showing the large deviations in both light chain and heavy chain of the antibody were same in all the MD conformers. The residue positions showing smallest deviations were same for all the conformers in the case of light chain, whereas relatively variable in the heavy chain. Positions of large and small deviations fell in the complementarity determining regions (CDRs), for both heavy and light chains. The larger deviations were in CDR-2 of light and CDR-1 of heavy chain. Smaller deviations were in CDR-3 of light and CDR-2 and CDR-3 of heavy chains. The large and small deviating regions highlight flexible and rigid regions of HH63 binding site and suggest a mosaic binding mechanism, including both "induced fit" and preconfigured "lock-and-key" type of binding. Combined "induced fit" and "lock-and-key" binding would be a better definition for the formation of large complexes, which bury larger surface area on binding, as in the case of antibody-HEL complex. We further show that flexible regions, comprising mostly charged and polar residues, form intermolecular interactions with HEL, whereas rigid regions do not. Electrostatic complementarity between HH63 and HEL also imply optimized binding affinity. Flexible and rigid regions of a high-affinity antibody are selected during the affinity maturation of the antibody and have specific functional significance. The functional importance of local inherently flexible regions is to establish intermolecular contacts or they play a key role in molecular recognition, whereas local rigid regions provide the structural framework.

Antibodies↗
PubMed2005

Gradient of rigidity in the lamellipodia of migrating cells revealed by atomic force microscopy.

Changes in mechanical properties of the cytoplasm have been implicated in cell motility, but there is little information about these properties in specific regions of the cell at specific stages of the cell migration process. Fish epidermal keratocytes with their stable shape and steady motion represent an ideal system to elucidate temporal and spatial dynamics of the mechanical state of the cytoplasm. As the shape of the cell does not change during motion and actin network in the lamellipodia is nearly stationary with respect to the substrate, the spatial changes in the direction from the front to the rear of the cell reflect temporal changes in the actin network after its assembly at the leading edge. We have utilized atomic force microscopy to determine the rigidity of fish keratocyte lamellipodia as a function of time/distance from the leading edge. Although vertical thickness remained nearly constant throughout the lamellipodia, the rigidity exhibited a gradual but significant decrease from the front to the rear of the lamellipodia. The rigidity profile resembled closely the actin density profile, suggesting that the dynamics of rigidity are due to actin depolymerization. The decrease of rigidity may play a role in facilitating the contraction of the actin-myosin network at the lamellipodium/cell body transition zone.

Actins↗
PubMedDate not supplied

[The use of rigid ureteroscope in the treatment of ureteral steinstrasse after extra corporeal shockwave lithotripsy of renal calculi--case report].

INTRODUCTION: Exracorporeal shockwave lithotripsy (ESWL) is the first choice for patients with urolithiasis. Increased use of endoscopic techniques provided increased use of ureteroscopic lithotripsy in the treatment of stones located in distal ureter, as well as ESWL. Rigid ureteroscope is usually used in the management of distal ureter stones, while middle and upper ureter stones should be treated by flexible ureteroscope or ESWL. At Urology Clinic in Novi Sad, ureteroscopy has been used since 1986, and more than 1000 procedures have been performed with success rate of over 95% (100% when we were able to reach the stone). The aim of this report is to show the destruction of stone along the ureter, using a rigid ureteroscope, shortly after the ESWL treatment of kidney stones. CASE REPORT: A 46-year-old woman was admitted to the Clinic with "steinstrasse" along the ureter, two weeks following ESWL of kidney stones. Primarily, she underwent ESWL without J-J stenting, at another urologic department. On admission to our Clinic, she complained of pain, nausea, mild temperature. An urgent diagnosis was carried out and left sided "steinstrasse" with hydronephrosis was confirmed by ultrasound, plain X-ray, laboratory findings. Ureteroscopy was performed under spinal anesthesia by rigid ureteroscope and the stone was destroyed along the ureter, even the pyelon was explored at the end of the procedure. The patient was advised to take a lot of fluids with diuretics and 80% of stones were eliminated in the first week after the procedure. At the first control, a month later, the patient was stone free. CONCLUSION: Rigid ureteroscope is a therapeutic option for distal ureteral stones, just as ESWL with comparable and reproducible results. This case confirms the fact that in strictly selected cases, and careful work of skilled urologists, rigid ureteroscope can be used for successful stone destruction in the middle and upper ureter.

Adult↗
PubMed1990

Test instrument for predicting the effect of rigid braces in cases with low back pain.

The difficulty of predicting the acceptance and the result of wearing rigid braces has been identified before and is reported in the literature. Therefore a test instrument has been developed and tested. The intention is that the test instrument can imitate a rigid brace. Furthermore, different attributes of the rigid brace can be altered. Thus the range of the lordosis, the level of maximal dorsal support and the amount of abdominal support can be altered. By changing these parameters the maximal pain relief is sought. A good correlation between the result in the test instrument and the rigid brace manufactured according to the information from the former was seen (93%). No false negative results were seen. Thus, if no acceptance or pain relief was seen in the test instrument no pain relief could be expected in a rigid brace. Another purpose of this test instrument is to simplify the manufacture of the brace and to transfer easily the information gained from the test instrument to the brace with the aid of a so called measuring device.

Adult↗
PubMed1997

Masseter muscle rigidity and nondepolarizing neuromuscular blocking agents.

Masseter muscle rigidity has been identified as a possible risk factor for malignant hyperthermia (MH) and is usually noted in children receiving intravenously administered succinylcholine chloride after mask induction with halothane. Nondepolarizing muscle relaxants are considered safe for persons susceptible to MH. In this article, we present a case of clinically recognized jaw rigidity in the absence of succinylcholine after administration of a non-depolarizing muscle relaxant that was reported to the Malignant Hyperthermia Association of the United States hot line. The patient had recurrent jaw rigidity during subsequent anesthesia when a different non-depolarizing muscle relaxant was given. The North American MH Registry was then reviewed for similar cases. Three cases of masseter muscle rigidity in the presence of nondepolarizing muscle relaxants were discovered. Two of the patients were not found to be susceptible to MH; however, the third patient had positive findings on muscle biopsy. These cases do not provide enough information to confirm the ability of nondepolarizing muscle relaxants to cause jaw rigidity in the absence of MH.

Adult↗
PubMed2000

Congenital muscular dystrophy with rigid spine syndrome: a clinical, pathological, radiological, and genetic study.

Rigid spine syndrome is a term first proposed by Dubowitz to describe a subset of patients affected by myopathy with early spinal contractures as a prominent feature. While spinal rigidity is a nonspecific feature, found in Emery-Dreifuss muscular dystrophy and in some congenital myopathies, it is also a prominent feature in a group of patients with merosin-positive congenital muscular dystrophy, where it is generally associated with stable or only slowly progressive weakness and early respiratory insufficiency. Recently, the first locus for congenital muscular dystrophy in association with rigid spine syndrome was mapped to chromosome 1p35-p36 in consanguineous Moroccan, Turkish, and Iranian families. We present here a detailed phenotypic description of the familial syndrome linked to this locus, describing 4 siblings (3 boys and 1 girl) of Northern European-American heritage who are the offspring of a nonconsanguineous marriage. All 4 siblings were affected by hypotonia and prominent neck weakness in infancy, early spinal rigidity, and early scoliosis. After initial improvement, muscle strength stabilizes or slowly declines, and skeletal deformities and respiratory insufficiency supervene. Muscle biopsy in an affected child at age 9 months revealed minimal, nonspecific myopathic changes, leading to a diagnosis of "minimal change myopathy." Muscle biopsy in his sibling, at the age of 14 years, revealed chronic and severe myopathic (dystrophic) changes, with normal staining for laminin-2 and for proteins of the dystrophin-glycoprotein complex. A possible explanation for these biopsy findings is that magnetic resonance imaging of the thighs reveals stereotyped selective muscle involvement, with the selectivity more pronounced early in the disease course followed by widespread muscular signal abnormalities in the late stages of the disease. In this family, linkage to the chromosome 1p rigid spine syndrome locus (RSMD1) is supported by maximum LOD scores for several markers of 1.81 at theta = 0, representing the maximum statistical power possible for this family. In combination with the previous report, this syndrome is linked to the RSMD1 locus with a summated maximum LOD score of 6.29, and analysis of recombination events in our family narrows the previously reported RSMD1 locus to 3 centiMorgans.

Adolescent↗