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Biomedical subjects

H Alexander

Publications and source records attributed to H Alexander.

At least 127 records · Page 7Linked to original sources
PubMed1989

Long-term follow-up of achilles tendon repair with an absorbable polymer carbon fiber composite.

In this cooperative multicenter study for surgical repair of Achilles tendon rupture using a composite implant, 48 patients underwent 52 procedures. This implant is composed of filamentous uniaxially aligned carbon fibers coated with an absorbable polymer. This highly biocompatible implant acts as a scaffold for regrowth of collagenous tissue. The early strength of this repair is provided by the composite implant and by the rapid ingrowth and attachment of new tissue, which allows for an earlier and more vigorous rehabilitation program. Patients with a minimum follow-up of 1 year form the basis of this article. The overall average follow-up is 2.1 years. Three cohort groups were observed on a temporal basis and quantitatively evaluated at 1 year (N = 29), 18 months (N = 22), and 2 years (N = 20), respectively. These three groups demonstrated continuous improvement during the first postoperative year. A high level of function was maintained throughout the second year. Repair of chronic injuries (N = 15) was compared with repair of acute injuries (N = 12) at 1 year following surgery. Both groups greatly improved. However, the acute group had more serious preoperative deficits but improved to a slightly better overall level. Of the patients having at least 1 year follow-up, 86% had a good or excellent result. There was no increased morbidity associated with the use of the carbon implant.

Achilles Tendon↗
PubMed1989

Development and validation of a radioimmunoassay for serum melatonin.

A radioimmunoassay using N-[3-(4-hydroxy-3-[4-hydroxy-3- [125I]iodophenylpropionyl)]-5-methoxytryptamine as tracer for determination of melatonin in the serum of different species is described. Melatonin antisera were raised in rabbits by immunization with a bovine serum albumin conjugate of N-[3-(2-aminoethyl)-5-methoxy indole] hemisuccinamide. A single high affinity, specific antiserum was obtained. In contrast to previous studies, the tracer was synthesised in one step in the absence of water, giving an excellent yield of highly pure product. No chromatographic purification step was needed. Polyethylene glycol in combination with goat antirabbit immunoglobulins was used to separate bound and unbound tracer. Sera were delipidized with Lipoclean prior the extraction of melatonin with diethyl ether. This sample preparation allows the determination of melatonin in the presence of widely varying amounts of lipids in human, rat and hamster serum. Using this extraction procedure, the sensitivity of the radioimmunoassay was approximately 1 ng/l of serum. Dilutions of sera and of synthetic melatonin gave the same parallel response in the radioimmunoassay. High performance liquid chromatography analysis of a serum extract showed only one immunoreactive peak co-eluting with synthetic melatonin. Characteristic diurnal rhythms of melatonin were observed in all species. All assay components including standards and serum controls are stable for at least 1 year at 4 degrees C, thus facilitating the determination of melatonin in a routine laboratory.

5-Methoxytryptamine↗
PubMed1989

Hydroxyapatite ceramics and the nature of the bone-ceramic interface.

Hydroxyapatite ceramics have been used as bone implants in a number of experimental systems and clinical applications. We have developed a unique experimental model that allows study of the interface between bone and implant materials. A comparison of titanium and hydroxyapatite materials, using this model, has demonstrated the osteoconductive nature of hydroxyapatite and its ability to bond directly to bone.

Animals↗
PubMed1989

Lower extremity fractures: relationship to reaction time and coordination time.

The purpose of this study was to examine the possible relationship between delayed reaction time and slow coordination time as a contributing factor to lower extremity fracture. A simple reaction time tester and hand coordination tester were used to assess the relative times of reaction and coordination. Subjects were also questioned concerning their daily activity levels. A definite relationship was observed to exist between the times recorded and lower extremity fractures: subjects with lower extremity fractures exhibited delayed reaction times and longer coordination times. Moreover, shorter reaction times and coordination times were seen in those subjects who reported higher activity levels. Statistical analysis was performed on selected data which show an association of fracture with reaction time.

Adolescent↗
PubMed1988

[Multiple pregnancy following in vitro fertilization and embryo transfer].

In a 32 year old patient 14 eggs were harvested and inseminated with donor semen. Six embryos were transferred resulting in a triplet-pregnancy. In spite of a septic disease three preterm but healthy children were born by caesarean section 199 days after ET (male 1620.0; female 1180.0; male 1560.0). Up to nowadays there is not any handicap. We don't know a general but safe method for avoiding multiple pregnancies.

Adult↗
PubMed1988

BamHI E region of the Epstein-Barr virus genome encodes three transformation-associated nuclear proteins.

Recombinant vectors carrying DNA fragments from the BamHI E region of the B95-8 Epstein-Barr virus (EBV) genome were transfected into COS-1 cells, and the transient expression of EBV-encoded nuclear antigens (EBNAs) was analyzed by using polyvalent human antisera and rabbit antibodies to synthetic peptides. Vector DNA containing two rightward open reading frames in the BamHI E fragment, BERF2a and BERF2b, induced the expression of a nuclear antigen identical serologically and with respect to size to the larger of the two polypeptides previously designated as EBNA4 in B95-8 cells. An antigen corresponding to the smaller polypeptide was induced in cells transfected with constructs that contained two neighboring reading frames, BERF3 and BERF4. This antigen also reacted with a rabbit antiserum to the synthetic peptide 203, deduced from BERF4. Thus, the findings show that the two components of the EBNA4 doublet in B95-8 cells are encoded by separate genes. The antigen encoded by BERF2a and/or BERF2b has been designated as EBNA4 and the antigen encoded by BERF3 and/or BERF4 has been designated as EBNA6. Polyvalent human antisera detected EBNA4 and EBNA6 in 9 of 11 lymphoid cell lines carrying independent EBV isolates. In the remaining two lines, either EBNA4 or EBNA6 was not detectable.

Animals↗
PubMed1988

Comparison of event rates among three MONICA centres.

Data from three MONICA centres in Auckland (New Zealand) and Newcastle and Perth (Australia) are used to explore some of the issues involved in comparing event rates and case fatality among MONICA centres. Auckland and Newcastle follow the "hot pursuit" method of identifying and interviewing patients while they are still in hospital. Perth follows the "cold pursuit" method, in which patients are identified by search of computerized hospital records after discharge and all data are abstracted retrospectively from case notes. Fatal cases are identified by the same method in the three centres. The distribution of events by MONICA diagnostic classification varied among centres, with Perth having the highest proportion of definite myocardial infarction events and the lowest proportion of possible myocardial infarction events. These differences appear to be due to the different methods of event ascertainment and data collection, and to variations in post mortem rates between centres. For comparisons among these three centres, the categories of non-fatal definite myocardial infarction and of all coronary heart disease deaths (that is those in the MONICA categories fatal definite myocardial infarction, fatal possible myocardial infarction, and fatal cases with insufficient data) appear to be the most useful.

Adult↗
PubMed1988

Osteoconductive composite grouts for orthopedic use.

A composite of HA particulate and calcium sulfate hemihydrate has been developed. When this dry material is mixed with either sterile saline or water, the resulting mixture begins to gel. While in the gel or dough state, the composite can be manually inserted or injected under pressure into a bone defect where it sets in situ. The calcium sulfate acts as a binder to hold the HA particles in place. The subsequent resorption of the calcium sulfate leaves controlled porosity for bone ingrowth and attachment to the nonresorbable HA particulate. The combination of calcium sulfate and HA results in a composite with handling properties superior to those of HA alone. Calcium sulfate has a long history of medical use as an implant material. The biocompatibility of the material has been clearly established. The combination of HA and calcium sulfate is likewise extremely compatible as demonstrated in the present studies. Bone ingrowth concomitant with resorption occurs rapidly with efficient conduction of bone from particle to particle. Based on the experiments presented herein, the composite of HA and calcium sulfate may be a useful alternative or adjunct to autogenous bone grafting. Many questions, however, remain regarding long-term tissue response and bone remodeling as well as the efficacy of this material relative to bone grafting.

Alveolar Process↗
PubMed1988

[Micromanipulation of gametes and pre-implantation mammalian embryos--a review].

With the successful management of the in vitro fertilization and embryo transfer in humans and in several mammalians it became possible to introduce further methods of the cellbiology in the practice. One complex in this connection is hereby shown to be the micromanipulation on gametes and on preimplantative embryos. With this technique the way was opened for some procedures which are known as microfertilization, transplantation of the nucleus and gene transfer somatic gene therapy. With these experiments a broad field of possibilities would be opened although about these can be only speculated.

Embryo Transfer↗
PubMed1987

Chemistry of antibody binding to a protein.

The chemistry of antibody recognition was studied by mapping the antigenicity of the protein myohemerythrin with peptide homologs of the protein sequence. The results suggest that the entire protein surface is antigenic, but the probability of there being antibodies to a given site is influenced by local stereochemistry. Although accessible to an antibody binding domain, the least reactive positions cluster in the most tightly packed and least mobile regions and are closely associated with narrow, concave grooves in the molecular surface containing bound water molecules. The most frequently recognized sites form three-dimensional superassemblies characterized by high local mobility, convex surface shape, and often by negative electrostatic potential.

Antibodies↗
PubMed1987

Mechanisms of antibody binding to a protein.

The mechanisms of antibody binding to a protein were studied by an analysis of specific amino acid residues critical to nine antigenic sites on myohemerythrin. Rabbit antisera to the whole protein were assayed for binding to more than 1500 distinct peptide analogs differing from the protein sequence by single amino acid replacements. The results, combined with information from the three-dimensional crystallographic structure, were used to evaluate probable mechanisms of antibody binding at individual sites. The data from all sites examined indicate that initial binding to solvent-exposed amino acid residues may promote local side-chain displacements and thereby allow the participation of other, previously buried, residues.

Animals↗
PubMed1987

Site-directed serology with synthetic peptides representing the large glycoprotein G of respiratory syncytial virus.

A set of 23 nested 15-amino-acid-long peptides with overlaps of 5 amino acids, representing the complete extramembranous part of the large glycoprotein G of respiratory syncytial (RS) virus, was analyzed in ELISA against different sera containing virus-specific antibodies. Seven of the peptides reacted with rabbit hyperimmune sera against purified virions. In contrast, only one of these seven peptides reacted with murine monoclonal antibodies specific for G. In connection with RS virus infections in humans, increase of antibody titers against three peptides was found in about one-third of the cases. These three peptides were included among those identified by both murine and rabbit antibodies. The present findings may open possibilities for site-directed clinical serology in the case of RS virus infections.

Antibodies, Monoclonal↗
PubMed1987

The design and analysis of a laminated partially degradable composite bone plate for fracture fixation.

During the early stages of fracture healing, rigid internal fixation maintains alignment and promotes primary osseous union. Unfortunately, as healing progresses rigid fixation from bone plating can cause bone in the region of the plate to undergo stress protection atrophy. This can result in significant loss of bone mass and osteoporosis. Refracture of the bone upon device removal is a widely reported complication. In an effort to minimize or eliminate stress protection atrophy, we have designed a partially absorbable, fiber-reinforced bone plate. Ideally, such a plate gradually loses rigidity as the fracture heals, increasingly transferring stress to the bone. Stress protection may be avoided and removal of the device after healing may be unnecessary. Composite theory was used to determine an optimum fiber layup for a composite bone plate. Composite analysis suggested the mechanical superiority of a 0 degree/ +/ -45 degree laminae layup. Given this laminated design, a thermoplastic absorbable polymer (polylactic acid polymer) was reinforced with high-modulus carbon fiber to produce a semiabsorbable composite. Implant evaluation included optimizing fabrication techniques, thorough mechanical device testing, and implantation on canine femurs to determine biocompatibility and efficacy. The composite design proved to have superior static and fatigue properties to laminated or random fiber designs used previously. Two techniques for hole fabrication were tested. The production of screw holes during the molding process rather than machining postmolding, improved the mechanical integrity of the finished plate. Although the 0 degree/ +/- 45 degree carbon/polylactic acid composite possessed superior mechanical properties, it was unsuccessful in the in vivo environment. Water absorption and subsequent delamination made the plate flexible. Hypertrophic nonunions developed. Further development to prevent water intrusion and premature loss of mechanical properties is necessary.

Absorption↗
PubMed1987

Neuroleptic radioreceptor activity and clinical outcome in schizophrenia.

The relationship between serum haloperidol concentration and clinical response was examined in 27 schizophrenic inpatients between the ages of 18 and 56 years. All patients were treated with haloperidol, 20 mg/day for the first 2 weeks. Dosage adjustment after 2 weeks of treatment was made in seven subjects based on poor clinical response or side effects. Haloperidol activity was determined by the radioreceptor assay for neuroleptics on weeks 2 and 4 serum samples. The results indicated that higher radioreceptor activity levels, particularly above 22 ng/ml, were associated with poorer clinical response. The data suggest that radioreceptor activity levels are not at a steady state after 2 weeks drug treatment. Additionally, problems secondary to low sensitivity of the radioreceptor assay may limit its utility at low serum concentrations.

Adolescent↗
PubMed1986

Evaluation of polylactic acid-carbon mesh for repair of ventral herniorrhaphy.

Large ventral hernias are a difficult surgical problem. Previous attempts to repair large defects in the abdominal wall with prostheses have been associated with recurrences and infection. A filamentous polylactic acid-carbon tissue mesh is a possible alternative prosthesis. We evaluated and compared polylactic acid-carbon mesh and Marlex mesh in repairing a large defect of the abdominal wall in a rat model. The polylactic acid-carbon mesh led to as strong a repair as Marlex mesh for the same time periods postoperatively; furthermore, no infection was noted with the former, whereas a 5.3 percent incidence of infection was noted with Marlex mesh. One mesh disruption was also noted with Marlex mesh. Polylactic acid-carbon mesh was found to have a more marked fibrotic response and a lesser inflammatory response. Polylactic acid-carbon mesh, therefore, appears to be more biocompatible, with more fibrosis, less inflammatory reaction, and equal strength to Marlex mesh. It is therefore a more appropriate synthetic material for a large ventral herniorrhaphy.

Abdominal Muscles↗