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Biomedical subjects

J N Thompson

Publications and source records attributed to J N Thompson.

230 records · Page 13Linked to original sources
PubMed1966

The preparation and biological activity of methyl 5,6-epoxy-retinoate.

1. Oxidation of methyl retinoate with monoperphthalic acid gave methyl 5,6-epoxyretinoate, obtained as pale-yellow crystals, m.p. 89 degrees . 2. The structure of the epoxide was confirmed by its ultraviolet, infrared, nuclear-magnetic-resonance and mass spectra. 3. The biological properties of the epoxide were investigated in male and female rats, and were found to be qualitatively similar to those of retinoic acid and methyl retinoate. 4. When administered to male rats reared on a vitamin A-free diet, the epoxide permitted growth although it did not maintain good general health. 5. Rats given a vitamin A-free diet and supplements of the epoxide had degenerate testes. 6. Female rats, maintained on a vitamin A-free diet containing retinoic acid and given supplements of the epoxide during pregnancy, resorbed their foetuses and failed to deliver litters. 7. The threshold of the electroretinogram response in male rats reared on a vitamin A-free diet with supplements of the epoxide was elevated above normal and was similar to that of rats maintained with methyl retinoate. 8. The oral administration of the epoxy acid to rats did not result in the accumulation of the corresponding epoxy alcohol in their livers.

Journal Article↗
PubMedDate not supplied

Embolization techniques in vascular tumors of the head and neck.

Surgical excisions of vascular tumors of the head and neck are frequently associated with difficulties because of the potential of operative blood loss. The technique of selective percutaneous embolization before surgery has emerged as a valuable adjunct-and even alternative-to surgery in the management of such lesions. By reducing the blood flow to a vascular tumor or arteriovenous malformation, embolization techniques can be greatly facilitate surgical excision. The participation of a qualified invasive radiologist is essential. If cases are carefully selected and procedural details strictly adhered to this technique can be quite valuable to surgeons treating vascular lesions of the head and neck.

Adolescent↗
PubMedDate not supplied

Premeiotic clusters of mutation and the cost of natural selection.

Haldane stated that there is a cost of natural selection for new beneficial alleles to be substituted over time. Most of this cost, which leads to "genetic deaths," is in the early generations of the substitution process when the new allele is low in frequency. It depends on the initial frequency and dominance value, but not the selection coefficient, of the advantageous allele. There have been numerous suggestions on how to reduce the cost for preexisting genetic variation that goes from disadvantageous, or neutral, to advantageous with a change in the environment. However, the cost of natural selection for new alleles that arise by mutation is assumed to be high, based on the assumption that new mutant alleles arise in natural populations as single events [1/(2N) of the total alleles]. However, not all mutant alleles arise as single events. Premeiotic mutations occur frequently in individuals (germinal mosaics), giving rise to multiple copies of identical mutant alleles called a "cluster" (C) with an initial allele frequency of C/(2N) instead of 1/(2N). These clusters of new mutant alleles reduce the cost of natural selection in direct proportion to the relative size of the cluster. Hence new advantageous alleles that arise by mutation have the greatest chance of going to fixation if they occur in large clusters in small populations.

Computer Simulation↗
PubMedDate not supplied

Minute perilymph fistulas: vertigo and Hennebert's sign without hearing loss.

The clinical entity characterized by episodic vertigo and a positive Hennebert's sign in patients without hearing loss is described. The history of perilymph fistulas is reviewed. Minute perilymph fistulas of the oval window were documented surgically in five consecutive patients with this syndrome. All experienced relief of their symptoms after surgical correction.

Adult↗
PubMedDate not supplied

Perilymph fistulae: variability of symptoms and results of surgery.

A perilymphatic fistula of a labyrinthine window may initially present with various cochlear or vestibular symptoms. Vestibular perilymph leaks can occur spontaneously with or without hearing loss and are most readily diagnosed by a positive Hennebert's sign. Surgical correction is indicated and should initially consist of grafting of the perilymph leak. A significant incidence of recurrence warrants further investigation of grafting materials and techniques.

Adolescent↗
PubMedDate not supplied

Endoscopic management of subglottic stenosis with the CO2 surgical laser.

Recent advances in microsurgery of the larynx have heralded a new era in the endoscopic management of subglottic stenosis. The carbon-dioxide laser with bronchoscopic adapters can be successfully employed to reestablish an adequate subglottic lumen. Thirteen cases of subglottic stenosis were managed endoscopically with the carbon dioxide surgical laser. In 77% (10 of 13) of these patients, a satisfactory airway was reestablished within a one-year period. The technique of laser vaporization and the results of treatment are presented. The role of corticosteroid therapy, antibiotic therapy, tracheotomy, dilation, and laryngeal stenting is discussed.

Adolescent↗
PubMedDate not supplied

Hyperventilation following a large-scale hazardous-materials incident.

Actual or perceived exposure to hazardous materials may result in physiologic and psychological effects. However, hyperventilation following such exposures has not previously been reported. After a large-scale industrial release of oxides of nitrogen, five (29%) of 17 patients evaluated at a major trauma center were hyperventilating, as defined by arterial PCO2 <33 mm Hg, and nine patients (53%) had arterial PCO2 <37 mm Hg. First responders (rescue team members and paramedics) had a higher rate of hyperventilation than other occupational groups. Age, gender, marital status, decontamination, and mode of arrival were not significantly associated with hyperventilation, although marital status approached significance. This study suggests that hyperventilation may be a common reaction after hazardous-materials incidents, and that certain populations may be at increased risk for this condition.

Adolescent↗
PubMedDate not supplied

Precision parameters of methods of analysis required for nutrition labeling. Part I. Major nutrients.

Major components of foods and feeds are fat, protein, and carbohydrates. Fat and protein are determined by direct measurements that are interpreted as the quantity of the constituent. Carbohydrates are usually calculated by difference. For this calculation, values for moisture/solids, ash, and "fiber" are also needed. The readily available collaborative studies for the determination of these major components are reviewed in an attempt to assign precision parameters to validated methods of analysis. When a number of studies for the same analyte, in the same food, by the same method are available, it is seen that the precision parameters among laboratories (standard deviations, SR; relative standard deviations, RSDR) and the ISO maximum tolerable difference functions (repeatability value, r; reproducibility value, R) are not characterized by any conventional distribution. The precision data are best summarized as a median or average parameter and the interval containing the centermost 90% of reported values. Typically, the precision of methods of analysis can be expressed as a function of concentration only, independent of analyte, matrix, and method. The average RSDR value from each collaborative data set can then be used as the numerator in a ratio containing, as the denominator, the value calculated from the Horwitz equation: RSDR = 2 exp (1 - 0.5 log C) where C is the concentration as a decimal fraction. A series of ratios consistently above 1, and especially above 2, probably indicates that a method is unacceptable with respect to precision. By this criterion, only the protein (Kjeldahl) determination is unqualifiedly acceptable with a 90% interval for RSDR of 1 to 3% at C values above about 0.01 (1 g/100 g). Fat, moisture/solids, and ash are acceptable down to limiting concentrations in the region of 1 to 5 g/100 g, if a test portion large enough to provide at least 50 mg of weighable residue or volatiles is specified. Measurements of individual carbohydrates and fiber-related analytes have unexpectedly poor precisions among laboratories. The variability, although high, may still be suitable for nutrition labeling. Reliability of analyses for the control of labeling of the primary nutrients must be achieved through quality assurance programs that require strict adherence to the directions of empirical methods and the use of suitable reference materials for absolute methods.

Databases, Bibliographic↗
PubMedDate not supplied

Problems of official methods and new techniques for analysis of foods and feeds for vitamin A.

The official methods for measuring vitamin A and carotene in foods and feeds have evolved over several decades. New procedures are needed to permit the use of modern analytical techniques such as liquid chromatography (LC), and to expand the application of official methods to a wide variety of foods. Recent improvements in methodology are reviewed. Emphasis is often placed on the separations achieved by LC, but all factors that affect quantitation, such as sampling, preparation of standards, and protection of the vitamin against oxidation, must be considered in the development of new methods. Many approaches to analysis are possible because of the versatility of LC but not all of them can be used in official methods. Methods for milk, margarine, and feeds can be prepared now for collaborative assays. Although straightforward methods can be developed for the measurement of beta-carotene in certain foods, a full examination of provitamins will probably continue to require a flexible approach and special expertise.

Animal Feed↗