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Biomedical subjects

K Rim

Publications and source records attributed to K Rim.

12 recordsLinked to original sources
PubMed2000

Pharyngeal pressure analysis by the finite element method during liquid bolus swallow.

The human pharynx is unique, acting as a complex interchange between the oral cavity and the esophagus, and between the nasal cavity and the lungs. It is actively involved in the transport of food and liquid, producing the forces that guide the bolus into the upper esophagus and away from the adjacent larynx and lungs. This study developed a biomechanical computer model of the human pharynx, utilizing a finite element method (FEM). Control 2-dimensional cine computed tomography images were obtained during 10-mL barium paste swallows at 8 levels extending from the tongue base to the cricopharyngeal level in order to encompass the entire pharynx. Three-dimensional finite element models of the pharynx were reconstructed from the geometric information obtained from the images at each level. Using an inverse dynamic approach with the addition of known tissue properties, we analyzed the 8 models under estimated pressure histories during swallow. Within each model, changes in the cross-sectional intraluminal area were calculated and compared with the area from the computer-generated FEM model. Area matching allowed estimation of intraluminal pressure gradients during swallow. The estimated pressure gradients were distributed through a range from 10 to 55 mm Hg, varying from one region to another and showing different patterns for the upper 4 levels and the lower 4 levels. The contraction velocity for the upper 4 levels was much higher than that for the lower 4 levels. The higher contraction velocities and pressure gradients in the upper levels are consistent with the bolus velocities required for efficient swallow.

Biomechanical Phenomena↗
PubMed1999

Comparison of viscoelastic properties of the pharyngeal tissue: human and canine.

The viscoelastic properties of the human and canine pharyngeal tissue in tension were evaluated, based on both an experimental protocol-consisting of cyclic load, tensile stress relaxation, and incremental step load tests-and the quasi-linear viscoelastic theory. The reduced stress relaxation function and the elastic response of the pharyngeal tissues were derived from the experimental results specifically obtained from those tissues. The characteristic features of viscoelastic property were obtained for both human and canine pharyngeal tissues by applying the quasi-linear viscoelastic theory and compared with each other. The material properties of the pharyngeal tissue were sought to facilitate the three-dimensional biomechanical model of the pharyngeal function by using the finite element method.

Aged↗
PubMed1998

Evaluation of the viscoelastic properties of pharyngeal tissue.

The viscoelastic properties of the human pharyngeal tissue in tension were evaluated, based on both an experimental protocol-consisting of cyclic load, tensile stress relaxation, and incremental step load tests-and a quasilinear viscoelastic theory. The physical properties of the pharyngeal tissue were evaluated to facilitate the biomechanical modeling of human pharynx. The methodology described has potentially significant clinical importance when one considers engineering a similar type of tissue having the same material properties in the future. Qualitatively, the characteristic features of viscoelastic properties of human pharyngeal tissue were experimentally obtained. Then, the reduced stress relaxation function and the elastic response of the pharyngeal tissue were derived from the experimental results specifically obtained from this tissue, by applying the quasilinear viscoelastic theory. The mathematical expression for analyzing nonlinear viscoelastic properties of human pharyngeal tissue is presented, as is the experimental protocol to evaluate the tissue properties. The characteristic features of the tissue need to be considered when attempting to engineer this tissue equivalent, and the data generated can be utilized to evaluate the function of tissue when it is engineered.

Aged↗
PubMed1995

Comparisons of the thermodynamic properties of three nickel-titanium orthodontic archwires.

The unique memory property of thermodynamic wire is only partially understood. It is believed to result from the wire's inherent capability to markedly alter its atomic bonding forces as a function of temperature. This shape recovery phenomenon may be the result of a transition in crystal structure that occurs by deformation and cooling. When the transition is reversed, by heating, the structure reverts to its original form and abrupt property changes occur. The purpose of this study was to determine the transition temperature ranges (TTR) of three commercially available thermodynamic archwires and to determine the rate of recovery of the wires when bent to a uniform shape. A jig was constructed to hold the wires and was suspended in a water bath within a plexiglass box. The temperature of the water bath was gradually increased. A program was written to acquire a single video frame from a running video tape and then allow the operator to graphically overlay the position of each wire specimen. The results indicate that the TTRs for the three commercially available thermodynamic wires are of similar magnitudes (x = 6.7 degrees C, 6.2 degrees C and 6.7 degrees C). The greatest differences were in the standard deviations (1.3 degrees C, 2.2 degrees C and 3.7 degrees C) which may be a function of manufacturing during alloying of the wire and/or its heat treatment.

Analysis of Variance↗
PubMed1991

The effect of defect size on the stress concentration and fracture characteristics for a tubular torsional model with a transverse hole.

The maximum stress location and crack resistance of a tubular torsional model with varying transverse circular defects were determined by the use of experimental and global-local finite element modeling techniques. The experimental results showed that the reduction in torsional strength was inversely proportional to defect size. In addition, the maximum stress location around the defect was closely related to the normalized defect diameter. By measuring the shifted angle associated with each defect ratio, a linear relationship, delta theta = -6.28 + 0.55*(d/D), was determined. Finite element results indicated that the stress concentration factor, Kg, for a single-cortex defect is similar to that of a double-cortex defect of identical dimension. Application of the strain energy density (SED) theory proposed by Sih and Oliveira Faria (Fracture Mechanics Methodology, Martinus Nijhoff, The Hague, 1984), indicated that the fracture toughness, KIC, for large defects was greater than that for small defects. This implies that tubular structures with large defects have a greater resistance to crack initiation and growth.

Animals↗
PubMed1991

Measurement of finger joint angles and maximum finger forces during cylinder grip activity.

Finger joint angles and finger forces during maximal cylindrical grasping were measured using multi-camera photogrammetry and pressure-sensitive sheets, respectively. The experimental data were collected from four healthy subjects gripping cylinders of five different sizes. For joint angles, an image analysis system was used to digitize slides showing markers. During the calibration of the camera system, both the nonlinear least square and the direct linear transform methods were applied and compared, the former providing the fewer errors; it was used to determine joint angles. Data were collected from the pressure-sensitive grip films by using the same image analysis system as used in the collection of the joint angle data. The method of using pressure-sensitive sheets provided an estimation of the weighted centre of the phalangeal forces. Results indicate that finger flexion angles at the metacarpophalangeal and proximal interphalangeal joints gradually increase as cylinder diameter decreases, but that at the distal interphalangeal joint the angle remains constant throughout all cylinder sizes. It was also found that most of the radio-ulnar deviation and the axial rotation angles at the finger joints deviate from zero, but the deviations are small. For the force measurement, it was found that total finger force increases as cylinder size decreases, and the phalangeal force centres are not located at the mid-points of the phalanges. The data obtained in this experiment would be useful for muscle force predictions and for the design of handles.

Biomechanical Phenomena↗
PubMed1990

Maximum finger force prediction using a planar simulation of the middle finger.

Maximum isometric finger-grip forces were predicted using a biomechanical model for plane motion of the middle finger. In the course of this study, mathematical representations of tendon displacement, the moment arm of tendon at the finger joints and muscle force-length relationship were investigated. The information gathered was applied to the model to estimate the maximum grip force of the middle finger gripping cylinders of different sizes. Muscle force per unit physiological cross-section area of 30 N/cm2 resulted in good agreement with measured force. However, for finger postures having an acute proximal interphalangeal joint angle, the estimated force was greater than that measured. Various joint angles were applied to the model to simulate the wrist and finger postures not limited to the cylinder grip. In general the finger force was greatest with the wrist in its extended position and at acute flexion of the proximal interphalangeal joint. The maximum finger force occurred at reduced metacarpophalangeal joint angles as the wrist joint changed from an extended position to a flexed one. It is also postulated that muscle force-length relationship is an important factor in muscle force predictions. The data obtained by this research are useful for the design of handles and the current model is applicable to the analysis of hand postures for workers using hand tools.

Biomechanical Phenomena↗
PubMed1976

The normal range and position of the pineal gland on computed tomography.

Precise measurements with the Vanguard Motion Analyzer were made to determine the position of the pineal gland as shown on the Polaroid displays of 145 normal scans. The relatively midline positions of the gland are expressed in terms of percentage shift of the gland in these 145 normal cases is defined by a mean value of 0.8% with a standard deviation of 0.6%. More than 99% of normal CT scans can be expected to show a percentage shift of 2.6% or less.

Cephalometry↗
PubMed1976

Frontal ventricular dimensions on normal computed tomography.

The computerized axial tomographic examinations of 200 normal patients and volunteers between the ages of ten to 81 years were evaluated. Determination of the ratio between the width of the brain and a dimension representing the distance between the outer borders of the lateral ventricles was made at two levels. This ratio, the cerebroventricular index, seems to be a reliable indicator of ventricular size. The standards vary with the age of the patient.

Adolescent↗