Biomedical subjects

G T Yamaguchi

Publications and source records attributed to G T Yamaguchi.

4 recordsLinked to original sources

PubMed1996

Three-dimensional head kinematics and cervical range of motion in the diagnosis of patients with neck trauma.

OBJECTIVE: To create a statistical model using three-dimensional (3D) head kinematics and range of motion (ROM) to distinguish between people with whiplash syndrome and asymptomatic controls. STUDY DESIGN: Cross-sectional study to estimate validity of diagnostic measures. METHODS: Fifty-one asymptomatic controls (most of whom were women), 18-35 yr old and 30 matched whiplash trauma patients seeking care from suburban outpatient clinics were sought. 3D kinematic parameters of head motion were obtained during tracking tasks (e.g., flexion, extension, etc.) and cervical ROM was measured via a head mounted inclinometer. Their level of pain and disability was assessed via a self-administered neck disability index questionnaire and visual analog pain scale (VAS). RESULTS: A scoring system of biomechanical abnormalities derived from the vertical piercing point, its second derivative and symmetry during oblique tasks. The scores ranged from a minimum of 0 to a maximum of 3. A cutoff of > or = 0.5 correctly identified the greatest number of subjects and minimized false positives (sensitivity 77%, specificity 82%, likelihood ratio 4.5). ROM performed similarly well at a cutoff of 1 SD below the normative mean (sensitivity 77%, specificity 84%, likelihood ratio 3.9). CONCLUSIONS: There is potential for biomechanical analysis to objectively detect abnormalities. The statistical model yielded moderate to high sensitivity and specificity using 3D helical-axis parameters of the head and standard ROM. The model development will continue via this process in future studies. These data could be a first step toward the creation of useful, noninvasive protocols for the diagnosis and management of soft tissue trauma of the neck.

Adolescent↗

PubMed1995

A computationally efficient method for solving the redundant problem in biomechanics.

Determining the optimal set of musculotendon forces with which to produce a forward dynamic simulation of movement typically involves a huge investment of time and computational resources. A new, computationally efficient method is proposed that simultaneously achieves the desired trajectory and the dynamically optimized set of muscle stresses, and hence forces, according to the maximal endurance criterion function of Crowninshield and Brand (1981). Muscle-induced accelerations of the system resulting from unit stress contractions of individual muscles are superposed via the new pseudoinverse method to yield the desired motion trajectory. The method is tested on a control problem involving a five degree-of-freedom (DOF), 30 muscle, upper extremity model, which incorporates a dual rigid-body forearm to represent pronation and supination more adequately. The pseudoinverse method delivered the desired motion to within 0.25 degrees for each DOF during a three-second simulation. It is anticipated that the methodology can be easily and accurately applied to other highly redundant optimal control problems in biomechanics.

Acceleration↗

PubMed1990

Restoring unassisted natural gait to paraplegics via functional neuromuscular stimulation: a computer simulation study.

Functional neuromuscular stimulation (FNS) of paralyzed muscles has enabled spinal-cord-injured patients to regain a semblance of lower-extremity control, for example to ambulate while relying heavily on the use of walkers. Given the limitations of FNS, specifically low muscle strengths, high rates of fatigue, and a limited ability to modulate muscle excitations, it remains unclear, however, whether FNS can be developed as a practical means to control the lower extremity musculature to restore aesthetic, unsupported gait to paraplegics. A computer simulation of FNS-assisted bipedal gait shows that it is difficult, but possible to attain undisturbed, level gait at normal speeds provided the electrically-stimulated ankle plantarflexors exhibit either near-normal strengths or are augmented by an orthosis, and at least seven muscle-groups in each leg are stimulated. A combination of dynamic programming and an open-loop, trial-and-error adjustment process was used to find a suboptimal set of discretely-varying muscle stimulation patterns needed for a 3-D, 8 degree-of-freedom dynamic model to sustain a step. An ankle-foot orthosis was found to be especially useful, as it helped to stabilize the stance leg and simplified the task of controlling the foot during swing. It is believed that the process of simulating natural gait with this model will serve to highlight difficulties to be expected during laboratory and clinical trials.

Computer Simulation↗

PubMed1989

A planar model of the knee joint to characterize the knee extensor mechanism.

A simple planar static model of the knee joint was developed to calculate effective moment arms for the quadriceps muscle. A pathway for the instantaneous center of rotation was chosen that gives realistic orientations of the femur relative to the tibia. Using the model, nonlinear force and moment equilibrium equations were solved at one degree increments for knee flexion angles from 0 (full extension) to 90 degrees, yielding patellar orientation, patellofemoral contact force and patellar ligament force and direction with respect to both the tibial insertion point and the tibiofemoral contact point. The computer-derived results from this two-dimensional model agree with results from more complex models developed previously from experimentally obtained data. Due to our model's simplicity, however, the operation of the patellar mechanism as a lever as well as a spacer is clearly illustrated. Specifically, the thickness of the patella was found to increase the effective moment arm significantly only at flexions below 35 degrees even though the actual moment arm exhibited an increase throughout the flexion range. Lengthening either the patella or the patellar ligament altered the force transmitted from the quadriceps to the patellar ligament, significantly increasing the effective moment arm at flexions greater than 25 degrees. We conclude that the levering action of the patella is an essential mechanism of knee joint operation at moderate to high flexion angles.

Biomechanical Phenomena↗