Biomedical subjects

C T Brighton

Publications and source records attributed to C T Brighton.

At least 55 records · Page 3Linked to original sources

PubMed1990

Theoretical determination of the current density distributions in human vertebral bodies during electrical stimulation.

Electrical stimulation with a 60 kHz sinewave input signal, supplied via external plate electrodes on the skin surface, is presently being studied as a treatment for human systemic osteoporosis. In this paper, Maxwell's equations were solved for voltage and current density values at nodal points in a three-dimensional, anatomically-based, finite element grid model of the human trunk constructed from T5 to L5. Based on the dose response results from Luessenhop's castrated Sprague Dawley breeder rat experiment and our theoretical determination, the magnitude of the input current to the electrodes necessary to induce a response in the human vertebral body was determined. Four different electrode systems in current clinical use were evaluated, and the optimal input current determined. In addition, the effect of subcutaneous fat was studied.

Adipose Tissue↗

PubMed1990

Capacitive coupling as an adjunctive treatment for avascular necrosis.

The purpose of this study was to determine the effectiveness of capacitive coupling, a noninvasive method for applying electrical stimulation to biologic tissues, when used as an adjunct to decompression and grafting in the treatment of avascular necrosis (AVN) of the femoral head. It also compared the results of core decompression and grafting with nonoperative management. Forty patients with Stages I-III AVN of the femoral head were treated with core decompression and grafting. All wore capacitive coupling units with electrodes placed over the femoral head continuously for six months. One-half of these units were active and one-half were inactive. Patients were followed for two to four years. Results were determined by preoperative and postoperative Harris ratings, quantitative roentgenographic measurements, and the number of hips that required total hip arthroplasty (THA). After all evaluations were completed, patients were divided into stimulated and nonstimulated groups. Patients in both groups were similar regarding gender, etiology, and roentgenographic stage of involvement. Results were also compared to 55 hips previously treated symptomatically, without surgery or electrical stimulation. There were no fractures, infections, or other significant complications in any of the hips operated on. Hips treated with decompression and grafting, both with and without electrical stimulation, were more satisfactory than hips treated symptomatically in regard to roentgenographic progression and the need for THA. There was, however, no indication that the addition of capacitive coupling gave better results than decompression and grafting alone.

Bone Transplantation↗

PubMed1990

Alkaline phosphatase production by periosteal cells at various oxygen tensions in vitro.

A mammalian periosteal cell culture system was developed to investigate the metabolic response of fresh calf bone periosteal cells to various oxygen tensions in vitro. Two predominant cell phenotypes were seen in the culture system. A rapidly proliferating mat of alkaline phosphatase-negative cells supported the growth of overlying clusters of alkaline phosphatase-positive cells. The appearance and subsequent population growth of the alkaline phosphatase-positive cells correlated directly with increases in enzyme activity on biochemical assay. Alkaline phosphatase production was optimal at lower oxygen tensions (5%, 9%), which approximated capillary pO2. In addition, the preconfluence oxygen environment was more critical to the final expression of the enzyme activity than the postconfluence environment. The mechanism of the environmental regulation of alkaline phosphatase gene expression at various oxygen tensions is not known. Periosteal cells were highly sensitive to oxygen tension and expressed alkaline phosphatase enzyme activity at oxygen levels approximating capillary rather than atmospheric pO2.

Alkaline Phosphatase↗

PubMed1990

Articular cartilage preservation and storage. III. Quantitative zonal analysis of cytoplasmic components of stored versus in vivo articular cartilage chondrocytes.

The cytoplasmic components of chondrocytes in the various zones of articular cartilage of the medial femoral condyle of six-week-old male New Zealand white rabbits stored in tissue culture medium at 37 degrees in 5% CO2 and air were quantitated from electron micrographs, and the results were compared statistically with the cytoplasmic components of chondrocytes in the corresponding zones of in vivo articular cartilage. The major changes that occurred during storage were: (1) an increase in the amount of lipid bodies in chondrocytes in the tangential, transitional, and calcified zones; (2) a decrease in the number of holes in the cytoplasm of chondrocytes in the radial and calcified zones; (3) a decrease in the amount of endoplasmic reticulum in the radial and calcified zones; and (4) an increase in cell size and cytosol area in the tangential and transitional zones but a significant decrease in cell size and cytosol area in the calcified zone. Stored articular cartilage chondrocytes demonstrated cellular changes associated with aging, whereas in vivo articular cartilage chondrocytes demonstrated changes associated with degeneration. The matrix of stored articular cartilage in the tangential, transitional, and upper part of the radial zones showed a decrease in opacity due to a decrease in the number of collagen fibers per unit area of matrix, a condition termed "chondroporosis." This study demonstrates that articular cartilage stored in standard tissue culture medium under ideal physiological conditions is morphologically abnormal. Based on these findings, one would not expect such stored cartilage to remain functionally intact when transplanted to replace articular cartilage loss.

Animals↗

PubMed1989

Neutropenia complicating parenteral antibiotic treatment of infected nonunion of the tibia.

Fifty patients with posttraumatic tibial nonunion complicated by chronic refractory osteomyelitis were treated with intravenous antibiotics. Fifteen patients (30%) experienced 18 episodes of leukopenia; seven of these patients became neutropenic and three became severely neutropenic. No patient became neutropenic prior to the 20th day of antibiotic therapy. The classic findings of fever, pruritus, maculopapular rash, and eosinophilia did not correlate with either the onset or the severity of the neutropenia. Neutropenia can develop precipitously. Prevention of neutropenia is difficult in a patient population receiving long-term antibiotic therapy. Regular monitoring of the white blood cell count and differential cell count minimizes the risk of developing prolonged, severe neutropenia with potential complications. No patient in this series had any serious or infectious complication secondary to neutropenia.

Adult↗

PubMed1989

The effects of demineralized bone matrix and direct current on an "in vivo" culture of bone marrow cells.

Bone marrow cells (BMCs) from rabbit femora and tibiae were grown in diffusion chambers implanted in rabbit muscle. At 42 days 80% of the BMC chambers exhibited cartilage formation within them. Demineralized bone matrix added to the marrow cell suspension in the chamber accelerated the appearance and increased the number of chambers with cartilage. Mineralization of the cartilage also occurred earlier in the chambers with bone matrix. In a second experiment, a 5-microA direct current cathode in the bone marrow chamber increased the number of chambers containing cartilage from 50 to 80% at day 25. Mineralization also occurred earlier in the chambers with direct current.

Animals↗

PubMed1989

Cytosolic ionized calcium concentration in isolated chondrocytes from each zone of the growth plate.

In isolated chondrocytes from the growth plate, there is an increase in both the cytosolic ionized calcium concentration and in total cell calcium content as the cells approach the mineralization front. The reserve zone chondrocytes have a cytosolic ionized calcium concentration, [Ca2+]i, of 124 +/- 23 nM and a total cell calcium content, CaT, of 12.8 +/- 6.8 nmol/mg cell protein. Proliferative zone chondrocytes have a [Ca2+]i of 172 +/- 29 nM and a CaT of 16.1 +/- 11.8 nmol/mg cell protein. Hypertrophic zone chondrocytes have a [Ca2+]i of 273 +/- 49 nM and a CaT of 35.8 +/- 16 nmol/mg protein. Chondrocytes isolated from the entire growth plate have a [Ca2+]i of 132 +/- 29 nM and a CaT of 13.2 +/- 2.5 nmol/mg cell protein. Chondrocytes isolated from noncalcifying hyaline cartilage have a [Ca2+]i of 85 +/- 10 nM and a CaT of 11.5 +/- 1.4 nmol/mg cell protein. There appears to be a correlation between intracellular calcium accumulation, an increase in the intracellular ionized calcium concentration, and the process of cartilage matrix mineralization.

Animals↗

PubMed1989

The effect of ascorbic acid on the metabolism of rat calvarial bone cells in vitro.

Addition of 50 micrograms/ml sodium ascorbate to confluent cultures of isolated rat calvarium bone cells resulted in a 21% increase in DNA production, a 50-60% increase in incorporation of [14C]proline into collagenous and noncollagenous proteins, and a 200% increase in alkaline phosphatase activity; under identical conditions, [35S]sulfate incorporation into proteoglycans (glycosaminoglycans) was not affected. These results suggest that ascorbate may be important in maintaining or stimulating the osteogenic phenotype of normal bone cells.

Alkaline Phosphatase↗

PubMed1989

Proliferative and synthetic response of bovine growth plate chondrocytes to various capacitively coupled electrical fields.

In vitro monolayer cultures of growth plate chondrocytes isolated from newborn calf costochondral junctions were subjected to capacitively coupled electrical fields for 48 h. In part A, the electrical signal was a 60-kHz sine wave applied at different voltages so as to produce electrical fields at the pericellular level of 7, 20, 50, and 126 mV/cm. Incorporations of [3H]thymidine and [35S]sulfate were assayed to determine the effect of the above fields on cells proliferation and matrix synthesis, respectively. Proliferation was increased by 47% in the 20 mV/cm field whereas the same field decreased [35S]sulfate incorporation by 21%. These changes were significant at p less than 0.05 in both instances. In part B, the 20 mV/cm field was applied in a pulsed fashion to produce daily duty cycles of 100, 25, 2, and 0.25%. Incorporation of [3H]thymidine, [35S]sulfate, and [14C]proline per DNA were assayed. Results indicated that the 100, 25, and 0.25% percent duty cycles showed significantly (p less than 0.01-0.05) increased proliferation, whereas the 0.25% signal (5 ms on/495 ms off for 6 h/day) significantly decreased [14C]proline incorporation. We conclude that the biologic response of cells in vitro is signal specific, and that the total amount of electrical energy required to stimulate the growth plate chondrocyte to increased proliferation is very small since the total time the 0.25% duty cycle signal was only 3.6 min of a 24-h period.

Animals↗

PubMed1989

Field distributions in vertebral bodies of the rat during electrical stimulation: a parametric study.

The electrical field and current density distributions were found in the various tissues of a mathematical model of the experimental rat used to study systemic osteoporosis. The finite element method was used to solve the boundary value problem derived from Maxwell's equations using a quasistatic approximation for a 60 kHz external output signal applied via skin electrodes. A parametric study was done initially to determine the principle factors which effect the solution of the field in the vertebral bodies. Grid coarseness, model length, and intervertebral space width had little effect on the solution while trabecular bone and abdominal cavity conductivity values had strong effects. The two pair of transversely placed electrodes spaced by at least three vertebral bodies produced the most uniform field distributions and was used in the experimental rat model. The range of current density values in the trabecular bone was determined to be 3.0-5.0 microA/cm2 at the external output signal where evidence of a reversal of bone loss due to castration osteoporosis had been found in the experimental rat.

Animals↗

PubMed1989

Osteonecrosis of the femoral head. Results of core decompression and grafting with and without electrical stimulation.

The effectiveness of core decompression and bone grafting with and without electrical stimulation was investigated in patients with avascular necrosis (AVN) of the femoral head. One hundred sixteen hips with AVN had decompression and grafting; 74 were also treated with direct current (DC). The DC stimulation was via a coil inserted directly into the femoral head. These were compared to 55 hips with AVN treated nonoperatively. Hips treated with electrical stimulation showed less roentgenographic progression and achieved a better clinical score than hips treated with decompression and grafting alone. Both groups had a significantly lower incidence of arthroplasty than the nonoperated controls. One patient developed a pulmonary embolus, but there were no fractures or other complications. Decompression and grafting are safe and reasonably effective in retarding the progression of AVN. Supplemental electrical stimulation seems to improve the results even further.

Arthroplasty↗

PubMed1989

Subcellular regulation of the ionized calcium pool in isolated growth-plate chondrocytes.

At a low total endogenous calcium content, as in the reserve and proliferative zone chondrocyte, cells buffer their ionized calcium pool at a low steady state between 150 and 300 nM. The endoplasmic reticulum appears to be primarily effective in the regulation of the ionized calcium pool under these conditions. With calcium loading of 20 to 30 nmol Ca+2/mg protein, as in the hypertrophic zone chondrocyte, the cells buffer their ionized calcium pool at a higher steady state between 600 and 700 nM. The mitochondria appear to be primarily effective in buffering the cytosolic ionized calcium pool after calcium loading. These data suggest that in the growth plate as the chondrocyte approaches the mineralization front, there is an accumulation of intracellular calcium that results in the saturation of the capacity of the endoplasmic reticulum to buffer the ionized calcium pool at a low steady state. Under these conditions of calcium loading, there is an increase in the intracellular ionized calcium concentration and a shift toward mitochondrial buffering of this calcium pool. This study has clinical relevance because in the cartilaginous tissues of the growth plate and in fracture callus, the matrix mineralizes as a prerequisite step in the formation of bone. Intracellular calcium accumulation and calcium release appear to play a role in matrix mineralization. An understanding of how the chondrocyte regulates intracellular calcium homeostasis in states of calcium accumulation is important in the overall understanding of bone development and fracture healing.

Animals↗

PubMed1989

Treatment of castration-induced osteoporosis by a capacitively coupled electrical signal in rat vertebrae.

Castrated male Sprague Dawley rats were subjected to various capacitively coupled electrical fields for six and eight weeks at two and 4.5 months after castration, respectively, with pairs of electrodes that were located paraspinally on the surface of the skin dorsally at the eleventh thoracic and fourth lumbar levels. When the animals were killed, dry and ash weights per unit of volume (apparent density), elastic modulus, ultimate stress, work to failure, trabecular area fraction, and mean trabecular width were determined for selected vertebrae. The results indicated that a sixty-kilohertz, 100-microampere signal (a calculated current density of five microamperes root-mean-square per square centimeter and a field of twelve millivolts root-mean-square per centimeter) significantly reversed the castration-induced osteoporosis in the lumbar vertebrae and restored bone mass per unit of volume in rats that had been stimulated for eight weeks after castration.

Animals↗

PubMed1988

Direct extracellular electrical stimulation influences density dependent aggregation of fetal rat cerebrocortical neurons in vitro.

Cells isolated from fetal (E17) rat cerebral cortex form aggregates in a density-dependent manner. Direct current electrical stimulation influences the formation of neuronal aggregates by promoting neuronal survival at a calculated current density of 15 nA/cm2 (with an average calculated field strength of 1 microV/cm), and inhibiting neuronal survival at calculated current densities of both 1 nA/cm2 and 150 nA/cm2. Electrical stimulation had no observable effect on neuronal aggregation independent of its effect on cell survival.

Animals↗

PubMed1988

Pulsing electromagnetic field stimulation of the in vitro growth plate.

Specific pulsing electromagnetic fields (PEMFs) have been used to stimulate growth and repair of osteogenic tissues; however, the basis for this specificity is unknown. Previously, we determined the relevant electromagnetic field parameters of the clinically used PEMF and independently verified the beneficial effects of PEMFs on the rabbit fibula fracture healing model. The goal of the present study was to develop an in vitro model that would permit the effectiveness of various electric and magnetic field components of the PEMF to be determined. The costochondral junction (CCJ) of the 21-day-old rat was exposed in vitro to PEMFs with various electric and magnetic field component amplitudes. Response of this model to PEMFs was determined by nondestructive macrophotographic measurement of CCJ growth. Preliminary data indicated that temperature effects were present in this in vitro system. Subsequent experiments designed to separate the effects of temperature and PEMFs on the growth of CCJs in tissue culture were performed. Results indicate that accurate and frequent temperature measurements must be made for in vitro models being used to study effects of PEMFs. Small temperature differences induced by the coils used to produce PEMFs in the CCJ experimental system can have significant stimulatory effects, and the combined effects of temperature and PEMFs are not linearly additive in this model. Furthermore, our results suggest that thermal and PEMF stimuli could affect macrophotographically measured growth of the CCJ by separate mechanisms or could have a synergistic effect. Therefore, PEMF stimulation experiments should be performed under strictly "athermal" conditions.

Animals↗

PubMed1988

Capacitively coupled electrical stimulation of bovine growth plate chondrocytes grown in pellet form.

Pellets formed from isolated bovine growth plate chondrocytes were grown in various capacitively coupled electrical fields. The signals chosen were 0, 10, 100, 250, 500, 750, 1,000, and 1,500 V peak-to-peak, 60 kHz. The effect on cell proliferation and matrix production of these different voltages was determined by [3H]thymidine and [35S]sulfate uptake, respectively, Cyclic AMP assays were done to determine if increases in either thymidine or sulfate uptake were associated with changes in cAMP levels. Significantly increased cell proliferation occurred at 500, 750, and 1,000 V peak to peak. The calculated electric fields were 1.5 to 3.0 x 10(-2) V/cm. Proliferation was significantly inhibited at 1,500 V peak-to-peak with a calculated field of 4.5 x 10(-2) V/cm. Little if any change was seen in cAMP levels at 30 or 60 min following application of the appropriate electric signals.

Animals↗

PubMed1988

Changes in bioelectric potentials on bone associated with direct current stimulation of osteogenesis.

This study was designed to determine whether changes occur in the bioelectric potentials on bone during and after bone stimulation with a 20-microA direct current (DC) and whether the variations in bioelectric potentials are related to the variations in bone formation. The bioelectric potentials were recorded at different times on the rabbit distal tibial surface, during (current-on state) and after (current-off state) DC stimulation with a cathode implanted within the medullary canal. The new bone formed at the end of the experiment was quantitated and related to the bioelectric potentials recorded at current-on and current-off states, respectively. Direct current stimulation resulted in electronegative potential spike centered on the cathode tip while current was applied. After electrical stimulation was turned off, the residual potentials at the end of the experiment did not significantly differ from the initial values. Conversely, the time sequence of the changes was significantly different from the control to the experimental group. The variations in the induced potentials at current-on state were significantly related to the variations in bone formation. This study suggests the existence of a relationship among bioelectric potentials, DC stimulation, and osteogenesis.

Animals↗

PubMed1988

Increased cAMP production after short-term capacitively coupled stimulation in bovine growth plate chondrocytes.

Growth plate chondrocytes from newborn calf costochondral junctions grown in monolayer were subjected to a capacitive AC signal of 500 V peak to peak (P-P) at 60 kHz for 48 h and were analyzed for [3H]thymidine uptake. The stimulated chondrocytes showed a 130% greater uptake over unstimulated controls. Other newborn calf growth plate chondrocytes were stimulated at 500 V P-P at 60 kHz for 2.5, 5.0, 10.0, and 20.0 min and were analyzed for cAMP. Chondrocytes stimulated for 2.5 and 5.0 min showed a 142.8% (p less than 0.05) and 394.5% (p less than 0.01) increase over controls, respectively. The chondrocytes stimulated for 10.0 and 20.0 min showed no significant difference from the controls. It is concluded that short-term exposure of growth plate chondrocytes to an appropriate capacitively coupled field stimulates cAMP production, but longer-term application of the electrical field is ineffective.

Animals↗