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Biomedical subjects

A L Weber

Publications and source records attributed to A L Weber.

At least 19 recordsLinked to original sources
PubMed2001

The sugar model: catalytic flow reactor dynamics of pyruvaldehyde synthesis from triose catalyzed by poly-l-lysine contained in a dialyzer.

The formation of pyruvaldehyde from triose sugars was catalyzed by poly-l-lysine contained in a small dialyzer with a 100 molecular weight cut off (100 MWCO) suspended in a much larger triose substrate reservoir at pH 5.5 and 40 degrees C. The polylysine confined in the dialyzer functioned as a catalytic flow reactor that constantly brought in triose from the substrate reservoir by diffusion to offset the drop in triose concentration within the reactor caused by its conversion to pyruvaldehyde. The catalytic polylysine solution (400 mM, 0.35 mL) within the dialyzer generated pyruvaldehyde with a synthetic intensity (rate/volume) that was 3400 times greater than that of the triose substrate solution (12 mM, 120 mL) outside the dialyzer. Under the given conditions the final yield of pyruvaldehyde was greater than twice the weight of the polylysine catalyst. During the reaction the polylysine catalyst was poisoned presumably by reaction of its amino groups with aldehyde reactants and products. Similar results were obtained using a dialyzer with a 500 MWCO. The dialyzer method of catalyst containment was selected because it provides a simple and easily manipulated experimental system for studying the dynamics and evolutionary development of confined autocatalytic processes related to the origin of life under anaerobic conditions.

Catalysis↗
PubMed2001

History of head and neck radiology: past, present, and future.

Head and neck radiology has evolved during the century since the discovery of the x ray in 1895 by Wilhelm Conrad Roentgen. In the first few decades, conventional radiography was the diagnostic modality for evaluation of head and neck diseases. Special radiographic projections were designed to demonstrate abnormal processes in the paranasal sinuses, temporal bones, base of the skull, and neck. Barium examination with fluoroscopy was used for assessment of the pharynx and esophagus. Linear tomography, introduced in 1932, allowed the acquisition of sections that depicted abnormalities that were not clearly defined at conventional radiography. Linear tomography was further enhanced with the introduction of thin-section polytomography, especially of the temporal bone, in 1954. Computed tomography in 1972 and magnetic resonance imaging in 1982 improved our diagnostic capabilities by enabling location and characterization of tumors, cysts, and inflammatory processes in the head and neck and aiding in earlier diagnosis and treatment. Teaching of residents and fellows by an expanding staff of head and neck radiologists developed. The formation of the American Society of Head and Neck Radiology in 1977 provided a forum for postgraduate education and scientific exchange.

Forecasting↗
PubMed2000

CT and MR imaging evaluation of neck infections with clinical correlations.

Infection of the neck is a common clinical problem in all age groups, especially children and young adults. The clinical symptoms and signs are often suggestive of the diagnosis. Imaging studies including CT and MR imaging are frequently required to confirm the diagnosis but more importantly to localize the infectious process and search for and delineate an abscess cavity. Ultrasound has also been used in the evaluation of superficial neck infections, especially to determine fluid accumulation. Conventional films consisting of an anteroposterior and lateral view were the examination before the introduction of CT in 1972. Conventional films can still be used for a preliminary survey, especially of the retropharyngeal space when there is a question of a retropharyngeal phlegmon or abscess.

Abscess↗
PubMed2000

Neurogenic tumors of the neck.

Neurogenic tumors of the neck occur in children and adults. Important parameters to aid in the differential diagnosis are age at presentation, location, and a history of NF or multiple endocrine neoplasia. Schwannoma is the most common solitary neurogenic tumor in the neck and is usually seen in patients between 20 and 50 years of age. The plexiform neurofibroma and multiple localized neurofibromas are characteristic of NF1. MPNSTs are uncommon aggressive lesions that can arise de novo in patients with NF (10% to 30%) and postirradiation. Neuroblastic tumors consist of neuroblastoma, ganglioneuroblastoma, and ganglioneuroma. These tumors typically arise in the chest and abdomen but occasionally present as a primary neck mass. A neck mass with a histologic diagnosis of neuroblastoma is, however, more commonly metastatic from an abdominal neuroblastoma.

Adult↗
PubMed2000

Imaging of benign and malignant soft tissue tumors of the neck.

Soft tissue tumors of the neck are a heterogeneous group of neoplasms arising from adipose, muscular, and fibrous tissue. With the exception of lymphomas, they account for only a small fraction of neck masses. Nevertheless, accurate diagnosis is important since the behavior of these neoplasms differs markedly from each other and from other head and neck masses. Noninvasive imaging, usually with CT and MR imaging, plays an important role in diagnostic evaluation and treatment planning for these tumors. In some cases, imaging features may be suggestive of a single entity. In most cases, imaging is needed to assess the location and extent of the tumor prior to biopsy or excision. This article discusses imaging techniques used for such assessment, the imaging features that help to separate these neoplasms from other head and neck tumors, and the behavior and imaging features of each of the more common benign and malignant soft tissue tumors that occur in the neck.

Diagnostic Imaging↗
PubMed2000

The thyroid and parathyroid glands. CT and MR imaging and correlation with pathology and clinical findings.

Thyroid imaging approach is based on the preliminary clinical evaluation. Lesions that are smaller than 2 cm should be assessed with US, which is capable of discriminating masses as small as 2 mm and distinguishing solid from cystic nodules. US-guided FNAB provides tissue for cytologic examination of thyroid nodules. CT and MR imaging are indicated for larger tumors (greater than 3 cm diameter) that extend outside the gland to adjoining structures, including the mediastinum, and retropharyngeal region. Metastatic lymph nodes in the neck and invasion of the aerodigestive tract are also in the realm of CT and MR imaging. Thyroid nodules are categorized on scintigraphy as hot or cold nodules. Hot nodules are rarely malignant, whereas cold nodules have an incidence of 10% to 20% of malignancy. Calcifications (amorphous, globular, nodular, and linear) occur in adenomas and carcinomas and have no differential diagnostic features except for psammomatous calcifications, which are a pathognomonic finding in papillary carcinomas and a small percentage of medullary carcinomas. Papillary carcinoma is the most common malignant tumor (80%) followed by follicular (20% to 25%); medullary (5%); undifferentiated; anaplastic carcinomas (< 5%); lymphoma (5%); and metastases. Lymph node metastases are common in papillary carcinoma, 50% at presentation, and less common in follicular carcinomas. The metastatic nodes in papillary carcinoma may enhance markedly (hypervascular); show increased signal intensity on T1-weighted images (increased thyroglobulin content or hemorrhage); and reveal punctate calcifications. Localized invasion of the larynx, trachea, and esophagus occurs predominantly in papillary and follicular carcinomas; the incidence is less than 5%. Ectopic thyroid tissue may be encountered in the tongue (foramen cecum); along the midline between posterior tongue and isthmus of thyroid gland; lateral neck; mediastinum; and oral cavity. Goiter and malignant tumors, notably papillary carcinoma, may develop in ectopic thyroid tissue. Carcinomas may also arise in thyroglossal duct cysts, which develop from duct remnants between the foramen cecum and thyroid isthmus. Infectious disease of the thyroid gland is not common and the CT and MR imaging findings are similar as described under neck infection. Other types of inflammatory disorders including Hashimoto's thyroiditis, granulomatous thyroiditis, and Riedel's struma display no specific imaging features. Imaging studies may, however, be indicated to confirm a suspected clinical diagnosis and assess compromise of the airway (Riedel's struma). HPT is a clinical diagnosis in which hypercalcemia is the most important finding. Parathyroid hyperplasia, adenoma, and carcinoma represent underlying lesions. To relieve the patient's symptoms surgical extirpation is indicated. The surgical success rate without imaging is 95%. The indications for imaging studies vary but it is generally agreed that reoperation after a previous failed surgical attempt and suspicion of an ectopic parathyroid adenoma should be investigated by imaging. These consist of US, nuclear medicine studies, CT and MR imaging. US and technetium sestamibi scanning have the highest accuracy rate for localizing an adenomatous gland at and near the thyroid gland. Ectopic adenomas, particularly if they are located in the mediastinum, are preferrably investigated with CT and MR imaging with gadolinium and fat suppression. Carcinomas and parathyroid cysts are optimally evaluated by CT and MR imaging. On MR imaging adenomas are low in signal intensity on T1-weighted images, high in signal intensity on T2-weighted images, and enhance post introduction of gadolinium.

Carcinoma↗
PubMed2000

Sugars as the optimal biosynthetic carbon substrate of aqueous life throughout the universe.

Our previous analysis of the energetics of metabolism showed that both the biosynthesis of amino acids and lipids from sugars, and the fermentation of organic substrates, were energetically driven by electron transfer reactions resulting in carbon redox disproportionation (Weber, 1997). Redox disproportionation--the spontaneous (energetically favorable) direction of carbon group transformation in biosynthesis--is brought about and driven by the energetically downhill transfer of electron pairs from more oxidized carbon groups (with lower half-cell reduction potentials) to more reduced carbon groups (with higher half-cell reduction potentials). In this report, we compare the redox and kinetic properties of carbon groups in order to evaluate the relative biosynthetic capability of organic substrates, and to identify the optimal biosubstrate. This analysis revealed that sugars (monocarbonyl alditols) are the optimal biosynthetic substrate because they contain the maximum number of biosynthetically useful high energy electrons/carbon atom while still containing a single carbonyl group needed to kinetically facilitate their conversion to useful biosynthetic intermediates. This conclusion applies to aqueous life throughout the Universe because it is based on invariant aqueous carbon chemistry--primarily, the universal reduction potentials of carbon groups.

Carbohydrate Conformation↗
PubMed1999

Pseudotumor of the orbit. Clinical, pathologic, and radiologic evaluation.

Pseudotumor, Graves' disease, and lymphoproliferative disease are the most common ophthalmologic disease entities requiring evaluation by CT and MR imaging. A history of acute onset, pain, swelling, proptosis, and response to steroids are the classical findings. The radiologic findings are categorized according to location into dacryoadenitis, myositis, and sclerouveitis, with and without associated infiltrations. The inflammatory infiltrate, which is composed of polymorphic leukocytes, lymphocytes, and plasma cells interspersed with a variable amount of fibrovascular tissue, may be diffuse or localized. The preferred radiologic method used for assessment of pseudotumor is CT. MR imaging, however, is indicated for evaluation of the Tolosa-Hunt syndrome, which is characterized by an inflammatory infiltrate in the orbital apex and cavernous sinus leading to cranial nerve involvement with ophthalmoplegia. The clinical and radiologic constellation of findings allows a definitive diagnosis in most cases.

Cavernous Sinus↗
PubMed1999

Organization and outcomes of inpatient AIDS care.

OBJECTIVE: To compare differences in AIDS patients' 30-day mortality and satisfaction with care in dedicated AIDS units, scattered-bed units in hospitals with and without dedicated AIDS units, and in magnet hospitals known to provide good nursing care. METHODS: Data were obtained on 1,205 consecutively admitted patients in 40 units in 20 hospitals and on 820 of their nurses. RESULTS: Mortality was lower and satisfaction was higher for AIDS patients in dedicated AIDS units and in nursing magnet hospitals. Primary nursing, end-of-life care counseling, and discharge planning were also more common. Higher nurse to patient ratios and AIDS physician specialty services were strongly associated with lower mortality. Patient satisfaction was strongly associated with organizational control of care by bedside nurses. Homosexuals were more likely to be admitted to dedicated AIDS units, which largely explains the under-representation of minorities and women. CONCLUSIONS: Dedicated AIDS units and magnet hospitals offer important benefits to AIDS patients, including lower odds on dying within 30 days of admission, higher patient satisfaction, and care meeting professional standards. Better nurse staffing, AIDS physician specialty services, and more organizational control by bedside nurses improve patient outcomes.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Prebiotic amino acid thioester synthesis: thiol-dependent amino acid synthesis from formose substrates (formaldehyde and glycolaldehyde) and ammonia.

Formaldehyde and glycolaldehyde (substrates of the formose autocatalytic cycle) were shown to react with ammonia yielding alanine and homoserine under mild aqueous conditions in the presence of thiol catalysts. Since similar reactions carried out without ammonia yielded alpha-hydroxy acid thioesters (Weber, 1984a, b), the thiol-dependent synthesis of alanine and homoserine is presumed to occur via amino acid thioesters--intermediates capable of forming peptides (Weber and Orgel 1979). A pH 5.2 solution of 20 mM formaldehyde, 20 mM glycolaldehyde, 20 mM ammonium chloride, 23 mM 3-mercaptopropionic acid, and 23 mM acetic acid that reacted for 35 days at 40 degrees C yielded (based on initial formaldehyde) 1.8% alanine and 0.08% homoserine. In the absence of thiol catalyst, the synthesis of alanine and homoserine was negligible. Alanine synthesis required both formaldehyde and glycolaldehyde, but homoserine synthesis required only glycolaldehyde. At 25 days the efficiency of alanine synthesis calculated from the ratio of alanine synthesized to formaldehyde reacted was 2.1%, and the yield (based on initial formaldehyde) of triose and tetrose intermediates involved in alanine and homoserine synthesis was 0.3 and 2.1%, respectively. Alanine synthesis was also seen in similar reactions containing only 10 mM each of aldehyde substrates, ammonia, and thiol. The prebiotic significance of these reactions that use the formose reaction to generate sugar intermediates that are converted to reactive amino acid thioesters is discussed.

Acetaldehyde↗
PubMed1997

Energy from redox disproportionation of sugar carbon drives biotic and abiotic synthesis.

To identify the energy source that drives the biosynthesis of amino acids, lipids, and nucleotides from glucose, we calculated the free energy change due to redox disproportionation of the substrate carbon of (1) 26-carbon fermentation reactions and (2) the biosynthesis of amino acids and lipids of E. coli from glucose. The free energy (cal/mmol of carbon) of these reactions was plotted as a function of the degree of redox disproportionation of carbon (disproportionative electron transfers (mmol)/mmol of carbon). The zero intercept and proportionality between energy yield and degree of redox disporportionation exhibited by this plot demonstrate that redox disproportionation is the principal energy source of these redox reactions (slope of linear fit = -10.4 cal/mmol of disproportionative electron transfers). The energy and disproportionation values of E. coli amino acid and lipid biosynthesis from glucose lie near this linear curve fit with redox disproportionation accounting for 84% and 96% (and ATP only 6% and 1%) of the total energy of amino acid and lipid biosynthesis, respectively. These observations establish that redox disproportionation of carbon, and not ATP, is the primary energy source driving amino acid and lipid biosynthesis from glucose. In contrast, we found that nucleotide biosynthesis involves very little redox disproportionation, and consequently depends almost entirely on ATP for energy. The function of sugar redox disproportionation as the major source of free energy for the biosynthesis of amino acids and lipids suggests that sugar disproportionation played a central role in the origin of metabolism, and probably the origin of life.

Amino Acids↗
PubMed1997

Chronic maxillary atelectasis.

Chronic maxillary atelectasis is a descriptive term that refers to a persistent decrease in the sinus volume of the maxilla from inward bowing of the antral walls. Case reports with comparable clinical presentations have appeared sporadically in the literature; however, this disorder has remained poorly defined. The purpose of this study is to provide a formal definition of this condition by the establishment of diagnostic and staging criteria. A 10-year case analysis identified 22 adults, and a review of the literature revealed another 25. The average age at presentation in our study was 38.3 years. Most patients were symptomatic, and some presented with diplopia and hypoglobus. Inward bowing of the antral wall(s) and persistent opacification on computed tomography made the diagnosis. Chronic maxillary atelectasis was separated into three stages according to the degree of wall deformation. While most patients were symptomatic, a past history of absent or mild symptoms referable to the nose and sinuses was encountered more often in those patients with osseous wall deformation (p = .041). Mild or absent symptoms at the time of diagnosis should not be considered a negative risk factor for the development of facial deformity, especially if the sinus has features consistent with complete pneumatization. A middle meatal antrostomy appears to relatively safely correct the sinus problem, while orbital floor reconstruction for hypoglobus, found in stage III of the disease, can be accomplished effectively via a transconjunctival approach using a combination of bone allograft and porous polyethylene sheets.

Adult↗
PubMed1996

Paraorbital lesions.

Explore the source record for details and available documents.

Central Nervous System Neoplasms↗
PubMed1996

Graves' disease of the orbit.

Graves' disease, the most common orbital disorder, affects approximately 0.5 % of the population of the United States. It is the underlying cause in 15% to 28% of cases of unilateral exophthalmos and in 80% of cases with bilateral exophthalmos. Also called "thyroid-associated ophthalmopathy", autoimmune thyroid disease," "endocrine exophthalmos," and "thyroid eye disease", Graves' disease presents with enlargement of the extraocular muscles, increased orbital fat volume, and venous stasis caused by increased orbital pressure. This article discusses the clinical evaluation and radiologic findings of this common orbital disorder.

Diagnosis, Differential↗