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Biomedical subjects

R A Hart

Publications and source records attributed to R A Hart.

At least 19 recordsLinked to original sources
PubMed2001

Surgical treatment of thoracic spinal stenosis: a 2- to 9-year follow-up.

STUDY DESIGN: A retrospective investigation of the results of operative treatment of patients with symptomatic thoracic spinal stenosis. OBJECTIVES: To establish the effectiveness and define the limitations of surgical treatment for stenosis of the thoracic spinal canal. SUMMARY OF BACKGROUND DATA: In contrast to cervical and lumbar stenosis, symptomatic narrowing of the thoracic spinal canal is rarely encountered. Although the treatment of thoracic stenosis has been described in multiple case reports and in several small series with minimal follow-up evaluation, there are few studies of patients treated surgically for this condition with follow-up evaluation beyond 2 years. METHODS: Twelve patients who underwent operative decompression for symptomatic stenosis of the lower thoracic spine were followed up for an average period of 62.4 months. Surgery was performed on the thoracic spine alone in four cases and on the combined thoracolumbar spine in eight. Factors that were investigated included pain severity, lower extremity motor function, ambulatory status, and postoperative complications. RESULTS: The level of pain after surgery was decreased in eight patients and unchanged in four patients. Of the 10 patients with a motor deficit before surgery, eight had improvement of muscle function. Of the 11 patients with a gait disturbance before surgery, ambulatory status was improved in seven, unchanged in two, and worse in two. One patient lost neural function secondary to surgical intervention. There were five cases in which the early result subsequently deteriorated because of recurrent stenosis, spinal deformity/instability, or both. CONCLUSIONS: Thoracic stenosis can occur in isolation or, more commonly, in association with lumbar stenosis. Ideally, operative treatment should address all stenotic segments and directly decompress the primary anatomic abnormalities causing neural element compression. Although satisfactory short-term results can be expected, deterioration of the early outcome because of the potential for recurrent stenosis and deformity/instability at the thoracolumbar junction can sometimes be seen with longer follow-up evaluation periods.

Adult↗
PubMed2000

Acute cervical spinal cord injury secondary to air bag deployment without proper use of lap or shoulder harnesses.

The authors present a case report of a patient with cervical central spinal cord syndrome caused by a hyperextension injury after a motor vehicle collision in which the air bag deployed in the absence of shoulder or lap belt harnesses. The potential for cervical spine and spinal cord hyperextension injuries in passengers positioned in front of air bags without proper use of shoulder or lap belt harnesses is discussed. Cervical central spinal cord quadriplegia occurred with cervical spondylosis and kyphosis that was managed by early three-level cervical corpectomy in a 58-year-old patient. Early improvement in the patient's neurological status occurred but was incomplete at the time of this report. Cervical hyperextension injuries are possible in passengers positioned in the front seat of cars with air bags when shoulder or lap belt harnesses are not used properly. Previous biomechanical studies have documented the potential for these types of injuries.

Accidents, Traffic↗
PubMed1999

Collagen fibril diameter distributions in rabbit anterior cruciate and medial collateral ligaments: changes with maturation.

This study presents morphometric analyses of the collagen fibril diameters of rabbit anterior cruciate and medial collateral knee ligaments of New Zealand White rabbits (young, age two months and adult, age thirty-six to forty months). Measurements were made from transmission electron micrographs of transverse ligament sections of approximately 50,000x magnification. Statistically significant differences in the mean fibril diameters were found between the anterior cruciate and medial collateral ligaments of the thirty-six to forty month old animals (.069 +/- .005, .092 +/- .016 mm, p < .1); however, no statistical significance was found for differences between these ligaments in two month old animals (.077 +/- .006, .082 +/- .009, p > .1). These data support the idea that known differences in fibril distributions of adult rabbit anterior cruciate and medial collateral ligaments develop with maturation, and may reflect both the cellular environment in which the fibrocytes of these ligaments are subject to, as well as the developmental genetic program of these cell populations.

Animals↗
PubMed1998

Comparison of cardiac-induced endogenous fields and power frequency induced exogenous fields in an anatomical model of the human body.

Time-domain potentials measured at 64 points on the surface of a large canine heart, considered comparable with those of a human heart, were used to calculate the electric fields and current densities within various organs of the human body. A heterogeneous volume conductor model of an adult male with a resolution of approximately 6 mm3 and 30 segmented tissue types was used along with the admittance method and successive over-relaxation to calculate the voltage distribution throughout the torso and head as a function of time. From this time-domain voltage description, values of [E(t)] and [J(t)] were obtained, allowing for maximum values to be found within the given tissues of interest. Frequency analysis was then used to solve for [E(f)] and [J(f)] in the various organs, so that average, minimum and maximum values within specific bandwidths (0-40, 40-70 and 70-100 Hz) could be analysed. A comparison was made between the computed results and measured data from both EKG waveforms and isopotential surface maps for validation, with good agreement in both amplitude and shape between the computed and measured results. These computed endogenous fields were then compared with exogenous fields induced in the body from a 60 Hz high-voltage power line and a 60 Hz uniform magnetic field of 1 mT directed from the front to the back of the body. The high-voltage power line EMFs and 1 mT magnetic field were used as 'bench' marks for comparison with several safety guidelines for power frequency (50/60 Hz) EMF exposures. The endogenous electric fields and current densities in most of the tissues (except for organs in close proximity to the heart, for example lungs, liver, etc) in the frequency band 40-70 Hz were found to be considerably smaller, between 5% and 10%, than those induced in the human body by the electric and magnetic fields generated by the 60 Hz sources described above.

Adult↗
PubMed1997

A system for surgical staging and management of spine tumors. A clinical outcome study of giant cell tumors of the spine.

STUDY DESIGN: This study developed and independently applied a spine tumor classification system, referred to as the Weinstein-Boriani-Biagini system, in a retrospective analysis of a series of patients with spinal giant cell tumors from three institutions. OBJECTIVE: To evaluate factors of potential prognostic significance for recurrence of spinal giant cell tumors. SUMMARY OF BACKGROUND DATA: No prior reviews of patients treated with modern surgical techniques are available. METHODS: Charts and radiographs for 36 cases of spinal giant cell tumors were reviewed by an independent investigator. All patients had had recent clinical follow-up examinations. All patients were classified according to the Enneking system. A subgroup of 24 patients for whom preoperative computed tomography scans were available were classified using the Weinstein-Boriani-Biagini staging system. Outcome measures included pain, neurologic status, and tumor recurrence. RESULTS: Recurrence rates were substantially higher among patients treated with attempted surgical excision before referral to a tertiary care center (83% vs. 18%). There was a higher recurrence rate for tumors that involved the vertebral body and posterior elements in comparison with lesions residing in only anterior elements (24% vs. 0%). Tumors that had extra-osseous extension into the canal and into the paraspinous musculature had a higher recurrence rate than tumors either confined to the osseous compartment or with extension either into the spinal canal or externally into paraspinous planes, but not both (21% vs. 10%). CONCLUSIONS: These results indicate that the Weinstein-Boriani-Biagini system may prove useful in developing treatment algorithms and in assessing outcome for these rare and difficult lesions. At least in the case of giant cell tumors, the musculoskeletal tumor staging system as developed by Enneking for long bones suggests the ideal surgical margin and may provide information relevant to tumor recurrence rates. Additional aspects of tumor extent and location, however, may berelevant to primary tumor recurrence rates when the selesions occur in the spine.

Adolescent↗
PubMed1996

Genetic differences between nitrate-negative and nitrate-positive C. pseudotuberculosis strains using restriction fragment length polymorphisms.

Corynebacterium pseudotuberculosis has been classified into two biotypes according to ability to breakdown nitrate (Biberstein et al., 1971). Restriction enzyme analysis (REA) has shown to reflect this differentiation, but numerous bands generated by this technique make interpretation difficult (Songer et al., 1988). Restriction fragment length polymorphism's (RFLP's) has become an accepted genetic tool and was used in this study to determine if differences in nitrate reduction and other phenotypic characteristics could be identified genetically. Thirteen C. pseudotuberculosis isolates from four species of domestic animals from different parts of the world were investigated for phenotypic and genetic differences. Three closely related bacteria, Corynebacterium ulcerans, Actinomyces pyogenes (previously C. pyogenes),and Rhodococcus equi (previously C. equi) were included in the study to determine if the RFLP bands were unique to C. pseudotuberculosis. All C. pseudotuberculosis isolates were positive for urease production. Some differences in maltose and sucrose fermentation ability and nitrate reduction were recorded. Genetic differences were identified between the nitrate-positive group and the nitrate-negative group using non-radioactive ribosomal RNA (rRNA) probes Southern blotted to restriction digests of ApaI, PstI, and SstI. A small number of bands were seen, with distinct differences between the nitrate-positive and the nitrate-negative strains. No genetic variations were seen between strains which reflected differences in carbohydrate fermentation. Strains isolated from different animal species and from different parts of the world could not be differentiated genetically using these three restriction enzymes.

Animals↗
PubMed1996

Posterolateral approach for anterior resection and posterior stabilization of the upper cervical spine: a case report.

Surgical approaches to atlanto-axial lesions are generally accomplished by either anterior (transoral) or posterior approaches as dictated by the location of the lesion. In certain patients, these approaches are combined, either in a single or staged procedure. Mechanical stabilization is much more readily accomplished posteriorly, as this allows easy incorporation of the occiput. While the transoral approach allows excellent exposure of the bodies of C1 and C2, it entails substantial surgical trauma. We describe the case of a woman with destruction of the anterior portions of the C1 and C2 vertebrae by metastatic breast cancer addressed by simultaneous anterior tumor debulking and posterior instrumentation through a posterolateral approach to the upper cervical spine.

Aged↗
PubMed1995

The spread of Corynebacterium pseudotuberculosis infection to unvaccinated and vaccinated sheep.

The decrease in the prevalence of Corynebacterium pseudotuberculosis after two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA). Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfected sheep, were run separately for 40 months and shorn 5 times to promote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CLA was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep. Sheep vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infection rate, with 77% of the transmission occurring at the 4th and 5th shearings, without any discharging CLA abscesses being observed. This study supports the view that in Australian wool producing flocks, CLA spreads mainly from sheep with discharging lung abscesses to sheep with shearing cuts. Vaccinated sheep infected with CLA have 96% fewer lung abscesses compared with unvaccinated infected sheep and are therefore less likely to spread this disease to other sheep.

Animals↗
PubMed1995

Use of multifactorial analysis to develop aqueous two-phase systems for isolation of non-native IGF-I.

A high yield procedure was developed to solubilize and extract IGF-I from recombinant E. coli by adding chaotrope and disulfide reductant to alkaline fermentation broth. To enhance centrifugation performance and recovery yield, a salt/polymer aqueous two-phase extraction procedure was developed whereby soluble non-native IGF-I and biomass solids are enriched in separate liquid phases. To develop this extraction system a multifactorial experimental approach was used to simultaneously map the phase diagram and identify conditions to suitably partition IGF-I and cell remnants. The presence of urea in these systems tended to disrupt two-phase formation and solids sedimentation. This, in turn, constrained the concentrations of phase forming solutes which could be effectively used. Systems containing low levels of salt (less than about 4% w/w) and polymer (less than about 10% w/w) did not form two phases. Systems containing high levels of salt (greater than about 7% w/w) and polymer (greater than about 18% w/w) formed two phases with floating solids. Intermediate levels of salt (between about 4% and 7% w/w) and polymer (between about 10% and 18% w/w) formed two phases in which solids were enriched in the heavy phase. Systems in this latter desired category were produced with a variety of different salts and polymers and all enriched non-native IGF-I in the light phase. Highest recovery yield (about 90%) was obtained with systems composed of 5% sodium sulfate and 14% PEG-8000.(ABSTRACT TRUNCATED AT 250 WORDS)

Centrifugation↗
PubMed1994

Large scale, in situ isolation of periplasmic IGF-I from E. coli.

Human insulin-like growth factor I (IGF-I) accumulates in both folded and aggregated forms in the fermentation medium and cellular periplasmic space when expressed in E. coli with an endogenous secretory signal sequence. Due to its heterogeneity in form and location, low yield of IGF-I was obtained using a typical refractile body recovery strategy. To enhance recovery yield, a new procedure was developed to solubilize and extract IGF-I from cells while in fermentation broth. This method, called in situ solubilization, involves addition of chaotrope and reductant to alkaline fermentation broth and provides recovery of about 90% of all IGF-I in an isolated supernatant. To further enhance recovery, a new aqueous two-phase extraction procedure was developed which partitions soluble non-native IGF-I and biomass solids into separate liquid phases. This two-phase extraction procedure involves addition of polymer and salt to the solubilization mixture and provides about 90% recovery of solubilized IGF-I in the light phase. The performance of the solubilization and aqueous extraction procedures is reproducible at scales ranging from 10 to 1000 liters and provides a 70% cumulative recovery yield of IGF-I in the isolated light phase. The procedure provides significant initial IGF-I purification since most host proteins remain cell associated during solubilization and are enriched in heavy phase. ELISA analysis for E. coli proteins indicates that 97% of the protein in the light phase is IGF-I. Together, the techniques of in situ solubilization and aqueous two-phase extraction provide a new, high yield approach for isolating recombinant protein which is accumulated in more than one form during fermentation.

Escherichia coli↗
PubMed1994

New infection with Corynebacterium pseudotuberculosis reduces wool production.

The effect of natural Corynebacterium pseudotuberculosis infection on wool production and quality in sheep was examined in light of evidence that artificial C pseudotuberculosis infection causes wool production loss. A toxin ELISA was used to identify sheep that had been infected with C pseudotuberculosis. Greasy and clean fleece weights and fibre diameter were compared in infected and uninfected sheep. C pseudotuberculosis infection caused a 3.8 to 4.8% decrease in greasy wool production and a 4.1 to 6.6% decrease in clean wool production. C pseudotuberculosis infection did not affect fibre diameter. The effects of caseous lymphadenitis (the disease caused by C pseudotuberculosis infection) cause an annual loss of about $17 million in wool production to the Australian wool industry.

Abattoirs↗
PubMed1994

Effect of biosynthetic manipulation of heme on insolubility of Vitreoscilla hemoglobin in Escherichia coli.

Vitreoscilla hemoglobin (VHb) is accumulated at high levels in both soluble and insoluble forms when expressed from its native promoter on a pUC19-derived plasmid in Escherichia coli. Examination by atomic absorption spectroscopy and electron paramagnetic resonance spectroscopy revealed that the insoluble form uniformly lacks the heme prosthetic group (apoVHb). The purified soluble form contains heme (holoVHb) and is spectroscopically indistinguishable from holoVHb produced by Vitreoscilla cells. This observation suggested that a relationship may exist between the insolubility of apoVHb and biosynthesis of heme. To examine this possibility, a series of experiments were conducted to chemically and genetically manipulate the formation and conversion of 5-aminolevulinic acid (ALA), a key intermediate in heme biosynthesis. Chemical perturbations involved supplementing the growth medium with the intermediate ALA and the competitive inhibitor levulinic acid which freely cross the cell barrier. Genetic manipulations involved amplifying the gene dosage for the enzymes ALA synthase and ALA dehydratase. Results from both levulinic acid and ALA supplementations indicate that the level of soluble holoVHb correlates with the heme level but that the level of insoluble apoVHb does not. The ratio of soluble to insoluble VHb also does not correlate with the level of total VHb accumulated. The effect of amplifying ALA synthase and ALA dehydratase gene dosage is complex and may involve secondary factors. Results indicate that the rate-limiting step of heme biosynthesis in cells overproducing VHb does not lie at ALA synthesis, as it reportedly does in wild-type E. coli (S. Hino and A. Ishida, Enzyme 16:42-49, 1973).

Bacterial Proteins↗
PubMed1994

Effect of environment on insulin-like growth factor I refolding selectivity.

Recombinant human insulin-like growth factor I (IGF-I), a 70-amino-acid peptide containing three disulphide bonds, produces two monomeric and several multimeric species during refolding. To optimize production of correctly folded IGF-I, conditions which influence protein refolding, stability and solubility were systematically examined. Combinations of solution components and conditions were analysed to identify synergistic interactions which enhance or reduce refolding efficiency. IGF-I concentration had the largest effect on formation of correctly folded peptide, due to competing association reactions. Solution polarity had the next largest individual effect, both on the level of multimeric peptide and on the relative proportion of correctly folded to misfolded monomeric peptide. Salt type and concentration and chaotrope type and concentration also had large individual effects on the distribution of IGF-I forms produced. Solution polarity modulated the effects of many other conditions including chaotrope concentration, salt type and concentration, and osmolyte concentration. Simultaneously decreasing the solution polarity and increasing the salt concentration improved the yield of correctly folded IGF-I relative to either individual change. Optimum solution conditions for refolding were 2M urea, 1M NaCl and 20% (v/v) ethanol. A possible mechanism for the importance of solution polarity on IGF-I refolding is discussed.

Amino Acid Sequence↗
PubMed1992

Ultrastructural morphometry of anterior cruciate and medial collateral ligaments: an experimental study in rabbits.

This study presents morphometric analyses of collagen subfascicle area fraction and collagen fibril diameter distributions for the anterior cruciate (ACL) and medial collateral (MCL) knee ligaments from transmission electron micrographs of ligament cross sections of five mature, female New Zealand White rabbits. Statistically significant differences in subfascicular area fractions were found between the ACL and MCL (0.89 +/- 0.02, 0.97 +/- 0.01, respectively; p less than 0.001). Mean fibril diameters for the ACL and MCL were also significantly different (0.059 +/- 0.005, 0.085 +/- 0.011 microns, respectively; p less than 0.025). Fibril eccentricity (a measure of parallel alignment of collagen fibrils within the ligaments, defined as the ratio of minor to major axes of elliptical fibril outlines) was 0.89 +/- 0.03 and 0.85 +/- 0.08, respectively, for the ACL and MCL; these data were not significantly different (p greater than 0.1). The relative amount of variation in the pooled fibril diameter data due to variation between animals, ligaments, locations within ligaments, and among fibrils at individual locations are reported. The variation of fibril diameter distributions between the ACL and MCL was substantially greater than the variation between different locations within each ligament cross section as well as between different animals. The structural differences reported may help explain known differences in the biomechanical properties of the ACL and MCL.

Animals↗
PubMed1992

Epiphytic microflora on alfalfa and whole-plant corn.

Epiphytic microflora were identified and counted on four cuttings of alfalfa, each harvested at three stages of maturity, and on three whole-plant corn hybrids. Enterobacteriaceae were predominant on both crops. Yeasts and molds also were major epiphytic microorganisms on whole-plant corn. The group--including lactobacilli, pediococci, and leuconostocs, which are genera that produce lactic acid and thus are instrumental in silage preservation--constituted only a small proportion of the total population (less than .5%) on both crops. Lactate-fermenting clostridial spores were not detected on standing alfalfa, and occurrences of these spores on standing corn plants were due to soil contamination from rainfall prior to harvest. The numbers of epiphytic microorganisms, except for the lactobacilli, pediococci, and leuconostocs group, were higher on standing corn than on alfalfa. The epiphytic microflora on alfalfa increased with increasing temperature during the growing season. However, neither cutting number nor maturity affected the epiphytic microflora on standing alfalfa, and wilting following mowing had little effect on most populations. Higher temperatures during wilting increased yeast and mold counts but had no effect on other microbial counts. The chopping process tended to increase the epiphytic microflora populations compared with those on the standing crops, and the group containing lactobacilli, pediococci, and leuconostocs was most enhanced. Only yeast and mold counts on the chopped alfalfa increased with greater DM content and buffering capacity.

Animal Feed↗