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At least 1,531 records · Page 85Linked to original sources
PubMed2002

Pericarditis and pericardial effusion in acute ST-elevation myocardial infarction in the thrombolytic era.

BACKGROUND: Myocardial infarction-associated pericarditis is a common cause of chest pain following MI, its frequency depending on how it is defined. OBJECTIVES: To investigate the incidence of acute pericarditis and pericardial effusion in the acute phase of ST-elevation MI treated with thrombolytic therapy. METHODS: The study group comprised 159 consecutive patients fulfilling the criteria for acute MI who were admitted to our department during 18 months. Infarct-associated pericarditis was defined as the finding of a pericardial friction rub, a typical pleuropericardial pain, or both. All patients underwent physical examination of the cardiovascular system four times daily for 7 days, as well as daily electrocardiogram and echo Doppler examinations. RESULTS: Fourteen patients (8.8%) developed a friction rub and 11 patients (6.9%) had a mild pericardial effusion. Six patients (4.0%) had both a friction rub and pericardial effusion. Two patients had a friction rub for more than 7 days. Pleuropericardial chest pain was present in 31 patients (19.5%) but only 7 of them had a friction rub. The in-hospital mortality rate was 1.3% and no mortality was observed in the acute pericarditis group. CONCLUSION: The incidence of signs associated with acute pericarditis was lower in MI patients treated with thrombolysis, compared with historical controls, when a friction rub and/or pericardial effusion was present. There was no significant reduction in the incidence of pleuropericardial chest pain.

Adult↗
PubMed1983

[The normal and prosthetic hip. A comparison of different surfaces].

The authors made a study of the biomechanical features of the normal and the prosthetic hip with a special reference to the distribution of forces and the characteristics of low friction. In his conclusion, he points out that the normal hip constitutes a remarkable system for the distribution of pressure in that the bearing surfaces are increased in direct relation to the load. This mechanism only functions because of the absence of friction and for the same reason, the size of the femoral head does not have any particular mechanical importance. In contrast, in the prosthetic articulation, even the smallest load is localised to the polar region on a surface which becomes more limited the greater the modulus of elasticity of the two composing parts. Excessive pressure is not harmful as it may be in a normal hip. Friction constitutes one of the features of an artificial hip and may be a friction of rotation or a friction of leverage. To limit these phenomena to their maximum, the coefficient of friction should be made as low as possible and, as far as possible the diameter of the prosthetic head should be limited.

Biomechanical Phenomena↗
PubMed1996

In vitro evaluation of coils for endovascular therapy.

PURPOSE: To evaluate the physical characteristics and behavior of coils for endovascular therapy. METHODS: Mechanically detachable coils were constructed with simple helical (4 mm X 10 cm and 8 mm X 30 cm) and pretzel shapes (4 mm X 5 cm) made from three metals using 0.003- and 0.004-in wire. Stiffness or pliability, frictional resistance, shape memory, and coil stability were evaluated in vitro. RESULTS: The 0.004-in wire stock coils proved significantly stiffer when compared with the 0.003-in coils. Tungsten coils proved least pliable; platinum coils were intermediate in stiffness; and nitinol coils were softest. Frictional resistance in the catheter was greatest for stiffer coils. The 5-cm pretzel coil consistently created more frictional force than the 10- or 30-cm simple helical coils. Despite a shorter length, the 4-mm simple helical coil exerted more frictional force than the 8-mm coil. Stiffer metal coils constructed of larger-diameter wire (0.004 in) were more stable than softer coils. CONCLUSION: Stiffer coils exert greater frictional forces within the catheter and a greater resistive force during bending but are more stable after placement. Frictional forces also depend on the complex three-dimensional shape of the coil and the diameter of the turns in that shape rather than coil length. These data suggest that a family of coils of different metals is optimal for varied intravascular needs.

Alloys↗
PubMed1998

In vitro evaluation of a measurement method to analyze the interdental, mesially directed force.

In order to evaluate interdental forces as a benchmark for mesial drift, a measurement technique was tested and evaluated on a human specimen. The measurement technique is based on the principle that a mesially directed horizontal force (FH) within a complete dental arch has an effect on interdental friction at the points of contact. The dynamic force (FZ), needed to pull out a defined metal strip from the interdental space is equal to the interdental frictional force (FR). Assuming unmodified approximal surfaces and unchanged tooth mobility in a complete dental arch, relative modifications of the interdental frictional force level provide a way of measuring horizontal force fluctuations. The validity of this measurement technique was measured by applying mesially directed forces of 1 to 5 N to the distal surface of the 2nd molar in a human specimen. The frictional forces measured increased in proportion to the distally applied force. The mesially directed force on the 2nd molar was transmitted in the dental arch anteriorly up to the incisor region and resulted in an increase of frictional forces. The reproducibility of this measurement technique was tested by quantitative analysis of potential measurement errors in the human specimen. The effect on interdental force measurement of the speed at which the metal strip is pulled was evaluated in a range of 50 to 500 mm/min. At the maximum pulling speed of 500 mm/min, a maximum scatter of 8% was recorded. Dependency of the dynamic force on direction of pull was measurable only when the metal strip was angled at more than 15 degrees. Experimental tests on the human specimen confirmed that the measurement technique presented here is sufficiently valid and reproducible for clinical long-term studies of interdental forces.

Bite Force↗
PubMed2003

Distributing vertical forces between the digits during gripping and lifting: the effects of rotating the hand versus rotating the object.

During pinch grip we partition the vertical tangential forces at the digits according to the friction at the grip surfaces, and the mass distribution of the object. However, we cannot predictively partition the vertical forces to adjust to new frictional conditions after viewing a 180-deg rotation of an object with different textures at each grip surface. Hence, the processes that lead to predictive force partitioning may not access object representations, thereby suggesting that these processes are digit-specific. If this is true, then we should fail to predictively partition our fingertip forces when we rotate our hand. We tested this prediction by comparing the effects of object rotation with hand rotation for repeated lifts of an object that had one slippery grip surface and one rough grip surface. Subjects did not predictively redistribute the vertical tangential forces upon grasping the rotated object. Following object rotation, the vertical tangential force trajectories during the first 100 ms after contact indicated that 12/15 subjects failed to anticipate the reversed digit-friction relationships. All subjects appropriately partitioned the vertical tangential forces between the digits by the second lift after object rotation, confirming previous reports that sensory signals update the memory associated with lifting the object. In contrast, after hand rotation, 13/15 subjects anticipated the new digit-friction relationships and upon grasping the object immediately generated a steep rise in the vertical force trajectory at the rough surface. They also delayed the initial rise in vertical tangential force at the digit encountering the low-friction surface by approximately 65 ms. Thus, anticipatory partitioning of vertical fingertip forces is not strictly digit-specific. Internally driven motor plans can access the relevant memories or internal models for predictively partitioning the vertical tangential forces. It is not clear if this process involves rotating internal representations of fingertip force directly, or if the forces are derived after internally rotating a representation of the object. In contrast to the robust effects of vision on reach kinematics, or on wrist and finger configuration, visual signals about object rotation and orientation apparently do not influence vertical tangential fingertip forces.

Adult↗
PubMed2006

Biomechanics of smooth adhesive pads in insects: influence of tarsal secretion on attachment performance.

Many insects possess smooth adhesive pads on their legs, which adhere by thin films of a two-phasic secretion. To understand the function of such fluid-based adhesive systems, we simultaneously measured adhesion, friction and contact area in single pads of stick insects (Carausius morosus). Shear stress was largely independent of normal force and increased with velocity, seemingly consistent with the viscosity-effect of a continuous fluid film. However, measurements of the remaining force 2 min after a sliding movement show that adhesive pads can sustain considerable static friction. Repeated sliding movements and multiple consecutive pull-offs to deplete adhesive secretion showed that on a smooth surface, friction and adhesion strongly increased with decreasing amount of fluid. In contrast, pull-off forces significantly decreased on a rough substrate. Thus, the secretion does not generally increase attachment but does so only on rough substrates, where it helps to maximize contact area. When slides were repeated at one position so that secretion could accumulate, sliding shear stress decreased but static friction remained clearly present. This suggests that static friction which is biologically important to prevent sliding is based on non-Newtonian properties of the adhesive emulsion rather than on a direct contact between the cuticle and the substrate.

Adhesiveness↗
PubMed2004

Assessing floor slipperiness in fast-food restaurants in Taiwan using objective and subjective measures.

Slips and falls are major problems in occupational injuries in which floor slipperiness is a critical issue. Most of the studies on slipperiness assessments were conducted in laboratories. Field assessments are rarely reported in the literature. This study investigated floor slipperiness in seven kitchen areas of 10 western-style fast-food restaurants in Taiwan using both objective and subjective measurements which were conducted by friction measurements and by employees' ratings of floor slipperiness, respectively. The friction measurement results showed that the sink area had the lowest average friction in the kitchens. Employees, however, rated both the sink and back vat (chicken fry) areas as the most slippery areas. The Pearson's and Spearman's correlation coefficients between the averaged friction coefficients and subjective ratings for all 70 evaluated areas across all 10 restaurants were 0.49 and 0.45, respectively, with p < 0.0001 for both. The results indicate that average friction coefficient and perception are in fair agreement, suggesting that both might be reasonably good indicators of slipperiness.

Accidental Falls↗
PubMed2005

Hydrophilic-coated catheters for intermittent catheterisation reduce urethral micro trauma: a prospective, randomised, participant-blinded, crossover study of three different types of catheters.

OBJECTIVE: To compare two hydrophilic-coated (SpeediCath and LoFric and one uncoated gel-lubricated catheter (InCare Advance Plus) concerning withdrawal friction force and urethral micro trauma. METHODS: 49 healthy male volunteers participated in this prospective, randomised, blinded, crossover study of three different bladder catheters. The withdrawal friction force was measured, and urine analysis of blood, nitrite and leucocytes, microbiological analysis of urine cultures and subjective evaluation of the catheters were performed. RESULTS: 40 participants completed the study and were included in the analysis. SpeediCath exerted a significantly lower mean withdrawal friction force and work than the gel-lubricated uncoated catheter, whereas LoFric exerted a significantly higher mean friction force than both of the other catheters. The hydrophilic catheters caused less microscopic haematuria and less pain than the gel-lubricated uncoated catheter. Furthermore, 93% of the participants preferred the hydrophilic catheters. CONCLUSION: Hydrophilic-coated catheters perform better than uncoated catheters with regard to haematuria and preference. SpeediCath, but not LoFric, exerts less withdrawal friction force than InCare Advance Plus.

Adult↗
PubMed2005

Adaptations to normal human gait on potentially slippery surfaces: the effects of awareness and prior slip experience.

Prior knowledge of potentially slippery conditions has been shown to alter normal human gait in slip and fall experiments. Here we quantify the effects of two aspects of prior knowledge - awareness of a possible slip and prior slip experience - on normal gait. Sixty-eight subjects (40F, 28M) each walked over 48 high-friction surfaces (control trials) and 12 low-friction surfaces. Within- and between-subject changes in lower limb muscle activation, gait kinematics and ground reaction forces were analyzed in three non-slip control trials: one before and one after the first unexpected slip exposure, and a third after repeated slip exposures. Subjects knew they might slip in the latter two trials but not the first trial. Twenty subjects slipped during their first low-friction exposure (early slip group), 32 in later low-friction exposures (late slip group), and 16 subjects did not slip at all. Simultaneous changes in awareness and experience between the first two analyzed trials of the early slip group altered the muscle activity in both limbs, reduced the foot and knee angles at heel strike in the slip limb and reduced the ground reaction forces, impulses and utilized friction after heel strike in the slip limb. A change in only awareness between the first two analyzed trials of the late slip group produced the same kinematic changes seen in the early slip group, but only small muscle activity change and no kinetic changes. Subsequent slip experience in the late slip group produced the muscle activation and kinetic changes observed in the early slip group, but no further kinematic changes. These results showed that awareness of a potential slip primarily alters how the slip-limb approaches the floor, whereas prior slip experience primarily alters the anticipatory muscle activation and how the foot interacts with the floor. These muscle, kinematic and kinetic changes were consistent with a more cautious "normal" gait, and can reduce the external validity of slip and fall experiments.

Adolescent↗
PubMed2001

Resistance to sliding of self-ligating brackets versus conventional stainless steel twin brackets with second-order angulation in the dry and wet (saliva) states.

The frictional properties of conventional stainless steel brackets that were coupled with rectangular stainless steel archwires and ligated with stainless steel ligature wires and the frictional properties of closed self-ligating brackets coupled with the same archwires were compared in terms of second-order angulation. The slides of these self-ligating brackets passively restrained the archwires within the slots. As a control, the frictional properties of the opened self-ligating brackets, which were ligated with stainless steel ligature wires, were measured. The resistance to sliding of the conventional brackets and the opened self-ligating brackets were measured at ligation forces ranging from 200 to 600 cN and at angles from -9 degrees to 9 degrees. The resistances to sliding of the closed self-ligating brackets were measured at the same angles, but no external ligation forces were applied. In the passive configuration, the conventional brackets exhibited similar frictional resistance as the opened self-ligating brackets, whereas the closed self-ligating brackets exhibited no friction. In the active configuration, all brackets exhibited increased resistance to sliding as the angulation increased. At all angles, the resistances to sliding of the closed self-ligating brackets were lower than those of the conventional brackets because of the absence of a ligation force when the slide restrained the archwire.

Dental Stress Analysis↗
PubMed2001

Biomechanics of slips.

The biomechanics of slips are an important component in the prevention of fall-related injuries. The purpose of this paper is to review the available literature on the biomechanics of gait relevant to slips. This knowledge can be used to develop slip resistance testing methodologies and to determine critical differences in human behaviour between slips leading to recovery and those resulting in falls. Ground reaction forces at the shoe-floor interface have been extensively studied and are probably the most critical biomechanical factor in slips. The ratio of the shear to normal foot forces generated during gait, known as the required coefficient of friction (RCOF) during normal locomotion on dry surfaces or 'friction used/achievable' during slips, has been one biomechanical variable most closely associated with the measured frictional properties of the shoe/floor interface (usually the coefficient of friction or COF). Other biomechanical factors that also play an important role are the kinematics of the foot at heel contact and human responses to slipping perturbations, often evident in the moments generated at the lower extremity joints and postural adaptations. In addition, it must be realized that the biomechanics are dependent upon the capabilities of the postural control system, the mental set of the individual, and the perception of the environment, particularly, the danger of slipping. The focus of this paper is to review what is known regarding the kinematics and kinetics of walking on surfaces under a variety of environmental conditions. Finally, we discuss future biomechanical research needs to help to improve walkway-friction measurements and safety.

Accidental Falls↗
PubMed2006

Initial force and postural adaptations when pushing and pulling on floor surfaces with good and reduced resistance to slipping.

The objective of the present study was to determine whether differences in the frictional properties of a floor surface may affect the kinematics and kinetics of pushing and pulling. Eight male participants were required to push and pull a four-wheeled trolley over two level surfaces, on which were mounted floor coverings with good (safety floor) and reduced (standard floor) frictional properties. A psychophysical approach was used to determine the initial maximum acceptable horizontal force required to move the trolley over a short distance (3 m). Three-dimensional (3D) hand and ground reaction forces and 3D postures were measured during initial force exertions. The results showed that psychophysically derived measures of initial horizontal force and horizontal components of hand forces did not differ significantly between floor surfaces. Despite the ability to exert similar forces, the measured maximum coefficient of friction varied according to floor surface. These changes reflected significant alterations in vertical and horizontal components of ground reaction and vertical hand forces, suggesting that participants had maximized the frictional properties available to them. Postures also changed as a consequence of floor surface, with significant changes occurring in knee flexion and trunk extension. This study has shown that handlers involved in the pushing and pulling of trolleys are capable of adjusting posture and the direction of hand and foot forces in order to compensate for reduced levels of floor friction. This has particular relevance when assessing the musculoskeletal loads imposed on the handler and the likely mechanisms of injury resulting from variations in floor conditions when workers undertake pushing and pulling tasks in the workplace.

Adult↗
PubMed2002

"Slip and fall" theory--extreme order statistics.

Classical "slip and fall" analysis was reformulated in this paper to account for the stochastic nature of friction. As it turned out, the new theory, arising from this analysis, was a precise statement of the distribution function for the smallest value among n independent observations. This made it possible to invoke an important result from the asymptotic theory of extreme order statistics that reduced the theory to a simple and elegant relationship among the probability of slipping, the critical friction criterion, the distance traveled by the walker, and the average, spread and asymmetry of the distribution of friction coefficients. The new theory reveals that short walks lead to fewer falls; low friction floors are sometimes better than high friction ones.

Accidental Falls↗
PubMed2006

Stick, unstick, restick sticky films in the colon.

The main challenge in designing diagnostic devices able to move along the colon is their locomotion method. Manipulating friction with the colonic surface is a key requirement for their safe and atraumatic propagation. One possible solution is to generate friction by means of adhesive forces. For this reason, a diagnostic device can be covered with mucoadhesive films that are able to stick on the colonic surface by generating high static friction. For a smooth transition from static to dynamic regime, the mucoadhesive films should unstick just before the initialisation of motion. Experiments have shown that promoting cohesive fracture of the films by controllable air introduction does not lead to friction reduction sufficient for smooth unsticking. Introducing water at the film-colon interface, however, reduces the static friction significantly, and makes the device to unstick and slide smoothly without leaving film fragments on the colonic surface behind. If unsticking is initiated by means of air or water introduction, a new film is required each time the device is required to restick. As an alternative, the possibility of coating the device with environmentally-sensitive mucoadhesive polymers that can respond reversibly to external stimuli and alter their properties is discussed.

Adhesiveness↗
PubMed2001

Prediction of mechanical behaviors at interfaces between bone and two interbody cages of lumbar spine segments.

STUDY DESIGN: The effects of mechanical parameters at bone-implant interfaces of the lumbar spine segments were investigated under various combined loadings using the finite element method. OBJECTIVE: To investigate the mechanical behaviors at bone-cage interfaces of lumbar spine segments with two interbody cages (two thread inserts). SUMMARY OF BACKGROUND DATA: It is known that among many factors, relative micromotion at bone-implant interfaces can hinder bone growth into the surface pores of an implant. Loading conditions, mechanical properties of the materials, friction coefficients at the interfaces, and geometry of spinal segments would affect relative micromotion and spinal stability. In particular, relative micromotion is related closely to friction at bone-implant interfaces after arthroplasty. METHODS: A finite element model of human L3-L4 lumbar segments with two titanium interbody cages was constructed. This finite element model was used to investigate mechanical behavior at the bone-cage interface. Relative micromotion (slip distance on the contact surfaces), posterior axial displacement, and stress were predicted for changes of friction coefficients, loading conditions, and age-related material-geometric properties of the spinal segments. RESULTS: Relative micromotion (slip distance) at the interfaces was obvious at their edges under axial compression. The slip occurred primarily at the anterior edges under torsion with preload, whereas it occurred primarily at the edges of the left cage under lateral bending with preload. Relative micromotion at the interfaces increased significantly as the apparent density of cancellous bone or the friction coefficient of the interfaces decreased. A significant increase in slip distance at the anterior anulus occurred with an addition of torsion to the compressive preload. CONCLUSIONS: Relative micromotion is sensitive to the friction coefficient of the interfaces, the bone density, and the loading conditions. A reduction in age-related bone density is less likely to allow bone growth into surface pores of the cage. However, it is likely that the larger the disc area or pedicle diameter, the more stable the interbody fusion of the spinal segments.

Age Factors↗
PubMed2004

The John Charnley Award Paper. The role of joint fluid in the tribology of total joint arthroplasty.

The effect of joint fluid on the tribology (ie, lubrication, friction, and wear) of total hip arthroplasty has not yet been investigated adequately. In the current study, a friction assay was used to assess four hypotheses relating to the effect of human joint fluid and its principal components on the articulation of metal-on-polyethylene. First, joint fluid was found to produce a widely varying amount of friction between cobalt-chromium and polyethylene; this range exceeded the range produced when the articulation was lubricated by water or bovine serum. Second, it was shown that hyaluronic acid, phospholipid, albumin, and gamma-globulin were not acting as boundary lubricants, but that one or more other proteins (as yet unidentified) were responsible for reducing friction in this couple. Third, lower friction was found when oxidized zirconium alloy replaced cobalt-chromium as a bearing surface on polyethylene. Finally, a pilot study suggested that lubricin, which contributes to cartilage-on-cartilage lubrication, is not a protein responsible for the tribological variabiation found among joint fluid samples. The current study showed that joint fluid is a patient factor that influences the tribology of metal-on-polyethylene arthroplasty.

Animals↗
PubMed2006

Additive decomposition of shear strength in cohesive granular media from grain-scale interactions.

We study cemented granular media by introducing cohesive bonding (sliding or rolling friction and tensile strength) between grains in the framework of the contact dynamics method. We find that, for a wide range of bond parameters, the macroscopic angle of friction at the peak state can be split into three distinct terms of collisional, frictional and dilational origins. Remarkably, the macroscopic tensile strength depends only on the bond tensile strength, and the friction angle at the peak state is proportional to the dilatancy angle which varies linearly with sliding friction.

Algorithms↗
PubMed1999

Macular amyloidosis: etiological factors.

Macular amyloidosis is the commonest form of primary localized cutaneous amyloidosis; its etiology remains unclear. Various incriminating factors include genetics, sunlight, and friction. Seventy-five patients with a clinical diagnosis of macular amyloidosis (confirmed by at least two observers) were enrolled in the study. A detailed history was elicited in relation to the etiological factors and followed by cutaneous examination. Skin biopsy was performed in 44 patients. Amyloid deposits were demonstrated in 21 (48%) of the biopsies. The female to male ratio was over 3:1. Patients with skin type V had a more delayed onset than those with skin types III and IV. Two patients gave histories of regularly subjecting their skin to friction. There was no correlation between the sites affected and the sites subjected to friction, hair style of the patient, or the use of cosmetics. Family history was present in 7 (9.3%) patients. A majority, 44 (58.7%) of the patients, had involvement of both sun-exposed and sun-protected sites. To conclude, there was no direct correlation between macular amyloidosis and atopy, sunlight, or friction to the skin in our patients. Multiple factors may play a collective role in the genesis of macular amyloidosis to variable degrees. These include racial, familial, and environmental factors, atopy, sunlight, friction, and female gender.

Adolescent↗