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G V Cochran

Publications and source records attributed to G V Cochran.

At least 37 records · Page 2Linked to original sources
PubMed1987

Design considerations in development of a prototype, piezoelectric internal fixation plate: a preliminary report.

The piezoelectric internal fixation plate represents a new concept in orthopaedic implants. The purpose of this device is to provide stable bone fixation while delivering internally generated, microampere direct currents to prevent or treat nonunion of a fracture or osteotomy. Clinically, currents of this type have been effective in treatment of nonunion, but application has required separate, implanted, or external battery or radiofrequency powered circuits. The "piezoplate" being developed contains an integral piezoelectric element that generates current in response to either physiological loading such as weightbearing or to externally applied ultrasound. Currents are processed by a rectifying circuit for delivery to bone by electrodes. Specially designed series/parallel piezoelectric elements and dual processing circuits are required to generate optimum rectified currents from the low-frequency, high-voltage signals generated by weightbearing, as well as the high-frequency, low-voltage signals produced by ultrasound. This paper reports on the current status of development and describes design parameters of this device which combines the modalities of mechanical fixation and electrical stimulation in a single implant.

Animals↗
PubMed1986

Development of a modular wheelchair cushion for spinal cord injured persons.

This paper discusses a modular wheelchair cushion system intended for patients at moderate or low risk for developing pressure sores. With the use of components with different mechanical and physical properties the modular cushion produces improved performance compared with cushions comprising the individual components alone. In addition to achieving clinically acceptable interface pressures, this approach to wheelchair cushion prescription helps to accommodate individual preferences associated with stability, temperature dissipation, and resiliency. Mechanical tests were performed to demonstrate the underlying principles of the modular cushion. Tests with able-bodied subjects identified specific cushion configurations for different weight groups, offering alternative material configurations that may be selected at the discretion of the therapist or patient.

Body Weight↗
PubMed1985

Repeatability of phasic muscle activity: performance of surface and intramuscular wire electrodes in gait analysis.

Repeatability is an important consideration for gait analysis data that are being used as an adjunct to clinical decision making. An index of repeatability may be based on a statistical criterion (variance ratio) that reflects similarity of wave forms over a number of identical cycles. The purpose of this study was to use the variance ratio to assess the repeatability of phasic muscle activity recorded with surface and bipolar intramuscular wire electrodes during gait on 10 normal subjects. Variance ratios were calculated using rectified and smoothed electromyographic data recorded simultaneously from the two types of electrodes. Three measures of repeatability (reproducibility, reliability, and constancy--defined as the cycle-to-cycle, run-to-run, and day-to-day repeatability of phasic muscle activity) were used to compare the performance of the two electrode techniques. Results show that the reproducibility and reliability were better for surface electrodes than for intramuscular wire electrodes, and constancy was good for surface electrodes and poor for intramuscular wire electrodes. Repeatability improved with increasing smoothing window lengths but was better for surface electrodes than wire electrodes, irrespective of the smoothing window. This study indicates that surface electrode data represent a more consistent measure of activity of superficial muscles, if comparisons are to be made between gait data from different test days.

Adult↗
PubMed1985

Piezoelectric internal fixation devices: a new approach to electrical augmentation of osteogenesis.

Prototype testing has been accomplished on a piezoelectric, internal fixation plate. This device combines a piezoelectric material with an internal fixation device as an integrated structure that provides mechanical stability, together with self-generated electrical stimulation, for treating fractures and nonunion. In bench and animal tests we have demonstrated that cyclical loading can cause a device of this type to generate electrical charge while attached to bone. After rectification, direct currents within the range known to stimulate osteogenesis can be produced by weight-bearing loads. Furthermore, electrical output of the implants can be increased by externally applied ultrasonic energy. These twin developments add significantly to the potential armamentarium of devices to enhance bone healing.

Animals↗
PubMed1984

Ultrasound mapping of the buttock-cushion interface contour.

For patients susceptible to decubitus ulcers, wheelchair cushions and other body support surfaces must be prescribed with a view to providing a uniform distribution of buttock-cushion interface pressures. The capacity to distribute pressure uniformly at the support interface depends on the shape of the bony prominences, and the amount and mechanical compliance of the overlying soft tissue: an indication of this capability may be given by the indentation contour of the buttock-cushion interface. Using normal subjects, we devised a method for measuring this contour using ultrasonic dimension gauging techniques. Because the technique can describe the geometry of soft tissues deformed under load, it could make an important contribution to successful employment of analytical modeling to predict internal tissue stresses during sitting.

Body Weight↗
PubMed1984

Evaluation of transducer performance for buttock-cushion interface pressure measurements.

To assess the performance of transducers used clinically to measure pressure at the skin-cushion interface of seated patients, transducers were placed between slabs of gel and/or foam materials compressed between platens. The recorded pressures consistently exceeded the nominal pressures calculated using the surface area of the slabs. This overestimation, observed in both miniature diaphragm transducers and air cell transducers, appeared to result from preferential loading of the transducer due to insufficient structural compliance in the environs. On the other hand, air cell transducers placed at a skin-foam interface beneath the thighs of human subjects gave readings which agreed closely with subcutaneous tissue pressure measurements obtained from a wick catheter inserted at the same location. These results suggest that, although pressure measurements are prone to error due to load sharing, results obtained clinically from subjects on soft cushions are reasonably accurate because of the high compliance of human soft tissue and the foam. Under low loads these distribute the pressure equitably and avoid concentrations of load on the transducer.

Buttocks↗
PubMed1982

Model experiments to study the stress distributions in a seated buttock.

Mechanical stress states that develop in the buttock during sitting may exceed tissue tolerance and lead to decubitus ulcer formation in susceptible patients, such as those with spinal cord injury. The danger of this complication can be reduced by using suitable cushions to minimize stress magnitudes and gradients within soft tissues. In this investigation, a two-dimensional physical model of the buttock-cushion system was developed to aid in cushion design. The model consists of PVC gel simulating flesh, cast around a wooden core simulating the ischium bone. A grid etched on the gel permits measurement of strains via photographs of the undeformed and deformed model buttock supported by various cushion materials. The displacement field is analyzed, using a finite strain theory and a strain energy function, to obtain the "tissue stresses'. In this manner, the performances of five clinically used cushion materials were compared with respect to the high stress regimes developed in the model buttock.

Buttocks↗
PubMed1981

Subcutaneous interstitial fluid pressure during external loading.

Interstitial fluid pressure (IFP) distribution generated as a result of externally applied pressure (EAP) may play an important role in the etiology of decubitus ulcers. In the forelimbs of 10 thiopental sodium-anesthetized Yorkshire pigs, weighing 16-20 kg, we placed wick catheters 2-5 mm below the skin. After equilibration, we applied a pediatric cuff and added EAP. With zero EAP, the IFP was -3.9 +/- 1.4 (SD) mmHg. In each case of EAP, IFP as measured with the wick catheter increased and reached a plateau within 10-15 min. In normal tissues, IFP reached approximately 65-75% of EAP. When we created an edematous condition by preinfusing with excess saline, IFP was found to reach 100% of EAP. The total normal stress in the tissue, generated as a result of external cuff pressure, can be considered as a sum of interstitial fluid pressure and extranormal stress. Integrity of the fibrous network and pore fraction may be important in transmitting pressure to the fluid.

Animals↗
PubMed1981

Wheelchair cushion modification: device for locating high-pressure regions.

Location and geometry of bony prominences must be known in order to modify foam wheelchair cushions to reduce high seating pressures beneath patients susceptible to decubitus ulcers. A portable, adjustable "wheelchair barograph" has been built that will identify high pressure regions clinically by means of light patterns. No electronic readout is required to obtain accurate records of high pressure regions on the seating surface which may be added to the patient's record or used directly to mark locations for cushion modification.

Buttocks↗
PubMed1980

A comparison of sitting pressures on wheelchair cushions as measured by air cell transducers and miniature electronic transducers.

With increasing attention to cushion selection for patients subject to decubitus ulcers, greater efforts are being made to prescribe cushions based on individual need. Pressure measurements during sitting frequently are utilized as a clinical guide to the process of selection and fitting. To determine the relationship between pressure values recorded from different types of transducers, simultaneous measurements were made beneath the ischial tuberosities using a Scimedics air cell transducer on one side and a matrix of 5 Kulite electronic transducers on the other side of a subject while sitting on a series of 21 commercially available wheelchair cushions. Although these transducers are different in structure and function, statistically similar results were obtained. The air cell type of transducer appear to be more appropriate for routine clinical use, but caution is advised regarding interpretation of results in terms of absolute pressures due to the many variables involved -- these techniques are suitable primarily for comparative measurements to obtain the optimal seating support for a given patient.

Humans↗
PubMed1980

Wheelchair cushion effect on skin temperature, heat flux, and relative humidity.

For patients subject to decubitus ulcers, wheelchair cushions should be prescribed with knowledge of the cushion's effect on the thermal as well as mechanical environment of the skin. To define thermal effects that may be encountered during routine use, tests werr made on 24 commercially available cushions. Skin temperature, heat flux and relative humidity were measured under the ischial tuberosities of a normal 24-year-old man during a 1-hour period of sitting on each cushion. After 1 hour, skin temperatures increased by means of 3.4 C and 2.8 C on foams and viscoelastic foams and there were slight decreases in heat flux as compared with control values in air. On gels, skin temperatures remained constant and heat flux increased, while water "floatation" pads caused a mean skin temperature decreased of 2.7 C along with a marked increase in heat flux. Relative humidity at the skin cushion interface increased by 10.4%, 22.8% and 19.8% on foams, gels and water floatation pads, as compared with room air values. Representative cushions from each of the general types (foam, viscoelastic foam, gel and water floatation) also were subjected to 2-hour tests which indicated the measured parameters continued to change asymptotically.

Adult↗
PubMed1978

Fractures of the odontoid: a laboratory and clinical study of mechanisms.

Previous reports and a study of the mechanism of injury in 25 cases of fracture of the odontoid suggest that the fracture usually results from a high velocity force directed to the head, producing flexion, extension, or rotation of the upper cervical spine. In a laboratory biomechanical study using cadaver preparations, fractures of the odontoid were produced in 20 specimens from the upper cervical spine, which were loaded in failure in forward and lateral modes.

Adolescent↗
PubMed1977

A new intramedullary fixation device for the distal third of the femur.

A new fixation device was designed for fractures of the distal third of the femur. An additional use has been for the stabilization of supracondylar osteotomies. The device consists of two- pre-shaped rods which are inserted through the medial and lateral femoral condyles into the medullary canal. The proximal end is ductile and the distal end rigid. Cross compression screws through the distal condylar ends anchor the rods and provide additional fixation for inter-condylar fractures. The preliminary experience in 17 patients demonstrates case of insertion and satisfactory internal fixation.

Adolescent↗