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At least 325 records · Page 18Linked to original sources
PubMed1975

Site of initial excitation and current threshold as a function of electrode radius in heart muscle.

End-diastolic current thresholds have been measured in 13 open chested dogs as a function of electrode radius by stimulating the left ventricle with epicardial disc electrodes ranging in a radius from 0-3 mm to 9 mm. Thresholds for cathodal rectangular short stimuli as well as specifically for cathodal make stimulation, proved to be proportional to the electrode radius to the power 1-5. This relationship between radius and threshold can be explained theoretically, assuming that electrical stimulation results in a propagated depolarization front if a critical current density is reached somewhere in the myocardium. The current distribution measured over the electrode and the site of initial depolarization in the tissue are in accordance with this theoretical explanation.

Animals↗
PubMed1983

Interpretation of the stokes radius of macromolecules determined by gel filtration chromatography.

From a comparison of the gel chromatographic properties of large randomly-coiled polypeptides in 6 M guanidine hydrochloride and of large globular proteins, we found that the distribution coefficient was more closely correlated with the intrinsic viscosity-based Stokes radius than with the translational frictional coefficient-based Stokes radius. This means that the effect of the hydrodynamic flow of dissolved molecules during gel chromatography should be considered. The ratio of transport of solute by bulk flow as compared with that by net diffusion (i.e., Brownian motion) is large under some conditions. On the other hand, we consider that the distribution coefficient obtained in static equilibrium experiments should be determined by the translational frictional coefficient-based Stokes radius, since the solvent does not flow. On this basis, we discuss the meaning of the Stokes radius and the separation mechanism of macromolecules by gel filtration.

Chemical Phenomena↗
PubMed2001

Dynamics of water storage in mature subalpine Picea abies: temporal and spatial patterns of change in stem radius.

Internal water reserves in bark and foliage of trees contribute to transpiration (T) and play an essential role in optimizing water transport by buffering extreme peaks of water consumption. We examined patterns of stem shrinkage and their relationship to tree water dynamics. We measured fluctuations in root radius and stem radius at different stem heights, T of twigs at the top of the crown and sap flow velocities in stem sections of mature subalpine Norway spruce (Picea abies (L.) Karst.) trees over 2 years. The output of each sensor was coupled by physical functions to a mechanistic flow and storage model of tree water relations. The data verified the model-predicted lag in water storage depletion in response to the onset of transpiration and the lag increased with increasing distance from the crown periphery. Between the crown and stem base, the delay ranged from a few minutes to several hours, depending on microclimatic conditions and tree water status. Stem volume changes were proportional to the amount of water exchanged between the elastic tissues of the bark and the rigid xylem, indicating that the "peristaltic" wave of stem contraction along the flow path represented depletion of water stored in bark. On a daily basis, stems lost between 0.2 and 0.5% of their volume as a result of bark dehydration, corresponding to about 2 to 5 l of water. This water contributed directly to T. According to the model based on hydraulic principles, there are three main components underlying the dynamics of water storage depletion: flow resistance, storage capacities of needles and bark, and T of each tree section. The resistances and capacities were proportional to the response delay, whereas T in the lower parts of the tree was inversely proportional. The pattern of T within the crown depended on water intercepted by the branches. Because of these weather-dependent factors, there was no time constant for the response delay along the flow path. Nevertheless, the upper crown and the root section tended to have longer response delays per meter of flow path than the stem. The diurnal course of stem radius fluctuations represents the sum of all external and internal conditions affecting tree water relations; stem radius fluctuations, therefore, provide a sensitive measure of tree water status.

Picea↗
PubMedDate not supplied

Ventricular radius reduction without resection: a computational analysis.

Reducing a dilated left ventricle's radius by wedge resection lowers wall stress, improving performance. However, compliance falls, stroke volume improvement is limited, and, later, both functional deterioration and serious dysrhythmias are frequent. These all may result from loss of circumference, loss of contractile mass, and myocardial trauma, none of which would occur in geometric remodeling. One specific technique is bimeridianal restraint, which uses two indenting bars to remodel the left ventricle (LV) as two widely communicating "lobes" of reduced radius. Computational analysis of this technique, applied to the dilated ventricular dimensions of four pretransplant patients, showed that 20% radius reduction would be accomplished by two < or =18 mm wide bars, indenting the epicardium < or =8.3 mm with < or =6.4 mm greatest outward displacement. Projected stroke volume (SV) for the subject ventricles was then modeled and compared with projections for resected ventricles. Assuming that equally improved contractile fraction will follow equal radius reduction, however that reduction is accomplished, improvement is dramatic: if postresection remodeling SV were 1.0, 1.2, or 1.5 times baseline, then postgeometric remodeling SV would be 1.36+/-0.06, 1.66+/-0.05, or 2.14+/-0.04 times baseline, respectively. These results, preservation of contractile mass and circumferential length, complete reversibility, and minimal operative trauma, warrant study of implementing mechanical designs.

Cardiac Surgical Procedures↗
PubMedDate not supplied

The effect of pulmonic and aortic constriction on regional left ventricular thickening dynamics, geometry and the radius of septal curvature. Analysis by gated computed transmission tomography.

We evaluated the effects of aortic and pulmonic constriction on cross-sectional cardiac dynamics using prospectively gated computed transmission tomography (CT) in six dogs in order to evaluate 1) the effect of altering the end-diastolic trans-septal pressure gradient on the radius of septal curvature, and 2) the effect of right ventricular overload on regional left ventricular geometry and wall thickening dynamics. Cross-sectional CT data were obtained in a control state, at two incrementally higher levels of right ventricular end-diastolic pressure produced by constriction of the pulmonary artery (PA1 and PA2) and then at one higher level of left ventricular end-diastolic pressure resulting from acute aortic constriction (Ao). Using fluid-filled polyethylene catheters, we measured right and left ventricular pressures simultaneous with the image acquisition. The measured radius of septal curvature was then normalized by the calculated average radius derived from the left ventricular area at end-diastole. The end-diastolic radius of septal curvature ratio increased as delta [LVEDP-RVEDP] declined (from 1.03 +/- 0.13 at control; 1.20 +/- 0.18 PA2; 1.27 +/- 0.14 PA2 and 0.87 +/- 0.11 Ao). As this LVEDP-RVEDP gradient declined (ie, RVEDP increased in proportion to LVEDP) septal wall thickening declined (P less than 0.005), with significantly less change in left ventricular anterior or lateral wall thickening. With PA hypertension, LV end-diastolic volume and percent delta volume significantly declined (P less than 0.005) while RV end-diastolic volume increased. With PA pressure overload, septum-free wall distance declined (P less than 0.01) as did percent shortening along this dimension (P less than 0.01). We conclude that predictable changes in LV and RV dynamics occur when trans-septal pressure gradients change.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Internal fixation of distal radius fractures with dorsal dislocation: pi-plate or two 1/4 tube plates? A prospective randomized study.

BACKGROUND: Severely comminuted distal radius fractures can be treated by different methods. Our routine procedure in dorsal dislocated fractures is the dorsal stabilization with two 1/4 tube plates. The new pi-plate is an other device that matches optimally the anatomy of the distal radius and allows a near half-circumferential dorsal buttress of comminuted intraarticular and extra-articular radial fractures. METHODS: In a prospective randomized study, comminuted distal radius fractures with dorsal displacement were stabilized either with two 1/4 tube plates or with the pi-plate. All patients were reviewed at 1, 3, and 6 months after surgery by thorough clinical examination and standard radiographs of both wrists. Results were analyzed and compared in both groups. RESULTS: Subjective and objective results in the pi-plate group are disappointing. Although optimal anatomic results were achieved, the complication-rate was high (14.3%) and the range of motion was limited. At final review, extension and flexion of the injured wrist had recovered to an average of 67% of the normal, contralateral side. Radial and ulnar deviation were limited to 64%, whereas pronation and supination reached 89% and 87%, respectively. Overall, results were good to excellent only in 56%. In a comparable group of patients with similar fractures and stabilization with two 1/4 tube plates, 82% of patients achieved excellent to good results, wrist motion was significantly better (p < 0.05), and no complications occurred. CONCLUSION: With open reduction, cancellous bone grafting, and internal plate fixation in comminuted distal radial fractures, excellent results can be achieved. In our experience, we cannot recommend the 7pi-plate in its current shape and prefer to stabilize distal radius fractures and dorsal fragment dislocations with two 1/4 tube plates.

Adolescent↗
PubMed1999

A way to reduce the radius of rotation in brain SPET with a single-head system.

To optimize spatial resolution in single photon emission tomography (SPET), it is essential to minimize the radius of rotation. In brain studies, different methods have been used to avoid shoulder interference when the radius of rotation is minimized: rectangular fields of view, modifications to the shielding around circular detectors and fan or cone beam collimators. However, few single-head systems can adopt these developments, particularly older cameras. A non-standard image acquisition method to reduce the radius of rotation in brain SPET with a single-head gamma camera is presented. The method applies a defined transformation to the original acquired images, maintaining the whole of the brain inside the field of view without shoulder interference and meeting the condition: pixel size < or = FWHM/3. With this method, it is possible to reduce the radius of rotation to 16 cm and to obtain a transaxial spatial resolution of 15.98 mm, which is 3.5 mm less than with the standard method used in our laboratory. This procedure was implemented for a Siemens Gammasonics ZLC 3700 gamma camera and has been validated in single-slice brain phantom studies. The method has the advantage of not requiring any complex or costly hardware.

Brain↗
PubMed1997

Radius of curvature of the posterior surface of the cornea.

The radius of curvature of the posterior surface of the cornea was measured in the vertical meridian for 120 children aged 6 to 17 years, using a Purkinje image method. The mean radius of curvature (+/-SD) was 6.42 +/- 0.31 mm, with a range from 5.62 to 7.22 mm. The ratio of anterior to posterior corneal radius was 1.210 +/- 0.045 or 0.827 +/- 0.029 when expressed as a reciprocal. There was a significant correlation between the anterior and posterior corneal radius (y = 0.798x + 0.228, r2 = 0.45). The study provides data that may be applied to a four-surface schematic eye.

Adolescent↗
PubMed2002

Condylar Stabilizing Technique with AO/ASIF Distal Radius Plate for Colles' Fracture Associated with Osteoporosis.

The author established a new reduction and fixation technique for osteoporotic distal radius fracture with a use of AO/ASIF volar distal radius plate, referring to the condylar plating technique in distal femoral fracture. This technique is performed in three steps. First, distal fixation is through the insertion of buttress pins just beneath the subchondral bone with a convergent angle of 10 degrees to the articular surface under fluoroscopic assistance. Second, the proximal limb of the plate is lined up with the radius shaft so that the fracture is reduced automatically and anatomically. Third, by rotating the proximal limb of the plate ulnarly and lifting up the ulnar border of the articular surface, the fracture is fixed less than the contralateral ulnar variance, to apply an adequate tension on the triangular fibrocartilage complex (TFCC). This method represents a valuable treatment modality for the most frequent types of unstable distal radius in elderly women.

Journal Article↗
PubMed2004

Corrective osteotomy of the distal radius through volar approach.

Operative correction through the malunion has become a well-accepted reconstructive procedure for symptomatic malunited extra-articular fractures of the distal radius over the last 3 decades. Now that newer plates designed specifically for the volar fixation of dorsally unstable distal radius fractures by incorporating buttress pins and screws that lock to the plate are available, more and more surgeons prefer volar fixation of dorsally unstable distal radius fractures. In the mid 1970s, the senior author (U.B.L.) developed a technique for corrective osteotomy of dorsally tilted malunions of the distal radius using a radiovolar approach and a special plate. This technique was proved to be efficient in more than 400 patients.

Journal Article↗
PubMed1993

Proteins of the Golgi apparatus. Purification to homogeneity, N-terminal sequence, and unusually large Stokes radius of the membrane-bound form of UDP-galactose:N-acetylglucosamine beta 1-4galactosyltransferase from rat liver.

The Golgi marker enzyme, UDP-galactose:N-acetylglucosamine beta 1-4galactosyltransferase (beta 1-4GalT) was purified 44300-fold in its intact, membrane-bound form from rat liver membranes. The protein was isolated from detergent extracts as a high-M(r) form, having a Stokes radius approximating a globular protein of M(r) 440,000. It is comprised of a single protein component as observed on SDS/polyacrylamide gels, having an M(r) near 51,000, and does not have intermolecular disulfide cross-links. N-terminal sequencing of the enzyme demonstrated that it contains an N-terminal hydrophobic stretch deduced previously from cDNA encoding for the enzyme. Previous studies have indicated that the protein may be translated at either of two AUG sites near the 5' end of the mRNA [Russo, R. N., Shaper, N. L. & Shaper, J. H. (1990) J. Biol. Chem. 265, 3324-3331], giving rise to two polypeptides, one appended with 13 amino acids. In the work described here, evidence was only found for the sequence of the short form, missing a single methionine at the N-terminus. Mild proteolytic treatment cleaved the enzyme, giving rise to low-M(r) forms which were fully catalytically active and which, upon sequencing, were missing a 66-amino-acid stretch from the N-terminus (as compared to the mouse cDNA). Proteolytic treatment was accompanied by conversion of the form having a large Stokes radius to one approximating a globular protein with M(r) near 50,000. The N-terminal stretch appears to contribute to maintenance of the form having a large Stokes radius. This may be the result of interaction with a detergent micelle, dimerization or oligomerization, or interaction with some other large, non-protein molecule, although a detergent exchange still resulted in a form having a large Stokes radius.

Amino Acid Sequence↗
PubMed1985

The central-peripheral radius of the normal corneal curvature. A photokeratoscopic study.

Both eyes of 40 normal persons were examined with a photokeratoscope. A method for analyzing the photokeratoscopic data based on the principle of least square fitting is presented. It is demonstrated that the corneal flattening expressed as the relative change in the radius of the corneal curvature is proportional with the square of the chord distances from apex. The factor of proportionality RV is defined as the coefficient of radius variation, which, together with the radius of the apex curvature K, are characteristic constants for a given meridian in a given eye. Expressed as mean and SD, the study demonstrates for the horizontal meridian K = 7.86 mm (0.25) and RV = 0.71 X 10(-2) mm-2 (0.26 X 10(-2)), for the vertical meridian the corresponding dimension are K = 7.65 mm (0.24) and RV = 0.70 X 10(-2) mm-2 (0.38 X 10(-2)). These results imply a change in the radius of the corneal curvature 1 mm and 5 mm from apex at, respectively, 0.7% and 17.7%. The precisions expressed as SD, by which the 2 parameters may be determined, are for K 0.03 mm and RV 0.12 X 10(-2) mm-2.

Adolescent↗
PubMed1986

Critical radius of endotherms.

The critical radius effect for insulation, well known in the engineering literature, was used by other authors to explain the lack of insulation on newborn endotherms. If that effect existed in small animals, they would lose less heat if nude than if fur or feathers were present. We show 1) that the previous analysis, although incomplete, yields the same result as a solid insulation model with the required sophistication and 2) that a proper model of fur is a porous media model. Neither of two porous media versions yield a critical radius effect. No critical radius effect occurs because simultaneous heat transfer by conduction and radiation makes it impossible to obtain the required logarithmic increase in thermal resistance with increasing insulation radius in a porous medium.

Animals↗
PubMed2002

One-radius triplets.

The one-radius triplet is an optical system that consists of three lenses. Either the radii of curvature of the lenses have the same absolute value or one radius of curvature has an infinitely large value. The advantage of such optical systems is that their production cost is less than that of systems with ordinary triplets. Here a theory of one-radius triplets is described and tables of parameters for their modification are provided. Residual aberrations are given for several selected triplets. One-radius triplets are suitable for use in laser technology and metrology.

Journal Article↗
PubMed2005

Correcting for stage error motions in radius measurements.

Traceable radius of curvature measurements are critical for precision optics manufacturing. An optical bench measurement is repeatable and is the preferred method for low-uncertainty applications. With an optical bench, the displacement of the optic is measured as it is moved between the cat's eye and the confocal positions, each identified using a figure measuring interferometer. The translated distance is nominally the radius of curvature; however, errors in the motion of the stage add a bias to the measurement, even if the error motions are zero on average. Estimating the bias and resulting measurement uncertainty is challenging. We have developed a new mathematical definition of the radius measurand that intrinsically corrects for error motion biases and also provides a means of representing other terms such as figure error-correction, wave-front aberration biases, displacement gauge calibration and their uncertainties. With this formalism, it is no long necessary to design a high-quality radius bench to carry out a precision measurement; rather a lower quality is adequate, provided that error motions are repeatable and characterized and error motion measurement uncertainties are estimated.

Journal Article↗
PubMed1997

Complex Articular Fractures of the Distal Radius: Classification and Management.

Articular fractures of the distal radius require an anatomic reduction, as even minimal step-offs are associated with the development of osteoarthritis. Such fractures are classified on the basis of both the mechanism and the pattern of injury. The comprehensive classification of fractures established by Muller et al defines those occurring from a shearing mechanism and involving part of the articular surface as type B fractures. These are in turn subdivided into group B1 fractures, which involve the radial styloid (chauffeur's fracture); group B2, which involve the dorsal margin of the radius; and group B3, which involve the volar margin of the distal radius (Barton's fracture). Type B fractures are unstable and often require operative intervention. Articular fractures resulting from a compression force on the end of the radius are classified as type C. A group C1 fracture is a two-part fracture without metaphyseal comminution; group C2, a two-part fracture with metaphyseal comminution; group C3, a fracture with more than two pieces, with or without comminution. The operative tactic for compression fractures involves restoration of the four common fragments in sequence. This can often be accomplished by manipulative means alone or with limited exposure of the fracture fragments and stabilization with percutaneous Kirschner wires. Neutralization with an external fixator and use of an autogenous bone graft are often required.

Journal Article↗
PubMed2003

[Screening for postmenopausal osteoporosis. Women with distal radius fractures should be evaluated for bone density].

In a case-control study at two country hospitals in Sweden, 110 consecutive postmenopausal women (age 50-75) with distal radius fracture were examined with the DXA-technique, on the injured radius, lumbar spine, and the right hip within three weeks after the fracture occurrence. Data was compared with 55 age-matched controls from The Swedish Population Register. The incidence of osteoporosis according to WHO's definition (T-score < -2.5) at any measurement site was higher in the fracture group, 44 per cent compared with 27 per cent in the control group. The fracture group had 12 per cent lower bone mineral density in the distal radius compared with the control group. A higher rate of previous fractures was noted in the fracture group compared with the control group. The study reflects the situation in general health care, where osteoporosis is common in postmenopausal women with distal radius fracture. This patient group can easily be identified and is suitable to be diagnosed for osteoporosis using bone density measurement prior to a decision being reached with regard to any treatment. According to the guideline for medical treatment (T-score < -2.0 and fragile-fracture) as outlined by the Swedish Osteoporosis Society, 75 per cent of postmenopausal patients with forearm fracture should be considered for such treatment.

Absorptiometry, Photon↗
PubMed2003

[Relationship between Hoover sign, functional and variables, and curvature radius in patients with obstructive pulmonary disease].

The purpose of the present study was: 1) to relate the Hoover sign -SH (+)- with several functional (spirometry and lung volumes) and radiographic (AP x-ray) parameters, 2) to characterize the changes in diaphragmatic curvature radius and the efficiency and to establish some relationships with the functional and radiographic parameters. Fifteen patients with COPD (SH (+), n: 8) were studied. The radius was determined in the right hemidiaphragm after maximal inspired and expired x-ray. The SH (+) was found in more severely obstructed patients (FEV1%, p 0.005%) and with high degree of air trapping (RV/TLC %, p 0.01). The expiratory radius (Re) was higher (p 0.05), and their efficiency (1/Re), was minor (p 0.05). The FEV1% correlated with the degree of hyperinflation according to TLC % (r -0.58, p 0.022) and with air trapping according to RV % (r -0.77, p 0.0008). The patients with low FEV1% showed high Re (r -0.61, p 0.015) and decreased diaphragmatic efficiency during expiration (1/Re) according to 1/Re = 0.093 cm-1 + 0.0012 cm-1* FEV1% (r 0.688, p 0.0054). The FEV1 correlated with the diaphragmatic movement (r 0.71, p 0.003). The PaCO2 correlated with the TLC % (r 0.534, p 0.04), the RV% (r 0.62, p 0.014) and with the radiographic parameters of hyperinflation (r 0.546, p 0.035) and air trapping (r 0.528, p 0.043). The presence of Hoover sign suggest severe bronchial obstruction, diaphragmatic flattening, increase of curvature radius, decrease of mobility and efficiency.

Aged↗