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Biomedical subjects

A Hoffman

Publications and source records attributed to A Hoffman.

At least 217 records · Page 12Linked to original sources
PubMed1986

Direct measurements on individual microcapsule dissolution as a tool for determination of release mechanism.

A method is described for simultaneous microscopic observation of individual microcapsule core material dissolution together with quantitative measurement of the individual kinetics of release of the contents. These may be conductimetric in the case of ionized materials or spectrophotometric otherwise. This enables correlation of changes in core surface area during dissolution with kinetics. Surprisingly, both ethyl cellulose- and polymethacrylate-coated cores of potassium dichromate crystals, used as a model, showed localized internal dissolution universally, providing evidence of the exit of the salt via pores in the membrane, in spite of the kinetics being invariably zero order, as expected for individual microcapsules. The advantages of the method are presented.

Acrylic Resins↗
PubMed1986

Families of schizophrenics: a movement in jeopardy.

The family self-help movement in schizophrenia is in danger of losing its effectiveness, the authors believe. Many in the movement seem overly concerned with being accepted by professionals and others, which means that they become less single-minded in their advocacy for their relatives and for their own needs. Family groups are having difficulty maintaining their separate and unique identity and are including others who tend to undermine their efforts. The family movement in schizophrenia would do well to follow the example of the parents of the developmentally disabled in their unswerving devotion to their cause, which appears to be the key to their success in achieving greatly increased services and funding.

Chronic Disease↗
PubMed1985

Obstructive sleep apnea induced by a parapharyngeal cystic hygroma in an infant.

A 7-week-old infant with severe sleep apnea underwent polysomnography that revealed as many as 455 obstructive apneas per night; the apneic episodes had a mean duration of 34 s. A growing tumor in the neck, a parapharyngeal cystic hygroma, was discovered and surgically removed. The infant's condition improved dramatically, and a follow-up polygraphic recording was normal. During the following 10 months the child's condition remained stable. The case reported illustrates a rare cause of severe sleep obstructive apnea. It also reinforces the need for a complete medical approach to the diagnosis and treatment of obstructive sleep apnea in infants.

Head and Neck Neoplasms↗
PubMed1985

Microencapsulation of paracetamol using polyacrylate resins (Eudragit Retard), kinetics of drug release and evaluation of kinetic model.

Methacrylate copolymers were used for microencapsulation of paracetamol by phase separation from chloroform with polyisobutylene 6% in cyclohexane. With polyisobutylene as an anti-aggregating agent, high quality microcapsules were obtained. Drug release appeared to fit both first order and Higuchi matrix model kinetics. However, on application of the differential rate treatment, the evidence supported the first order description, which was further supported by computed simulations of the models. Variation of production conditions showed that increasing the proportion of core material raised the microcapsule drug content and the release rate. Reduction of core particle size correlated with reduced coating thickness and faster release rate. The rate constants correlated with the estimated surface areas and wall thicknesses of the various batches. The data were used to estimate an apparent permeability constant for paracetamol in Eudragit RS microcapsules, which was constant and comparable with values found single core, non-aggregated microcapsules containing other similar drugs and different wall materials.

Acetaminophen↗
PubMed1985

Intratesticular adrenal rests diagnosed by ultrasound.

Adrenal rest tumors of the testes may occur in conditions associated with increased circulating adrenocorticotropic hormone (ACTH), including congenital adrenal hyperplasia (CAH) and Addison disease. Sonographically, these tumors appear as multiple round, hypoechoic nodules near the testicular hilus and are usually bilateral. They may undergo extensive fibrosis and become hyperechoic with acoustic shadowing. In the absence of excess ACTH or characteristic ultrasound findings, biopsy is recommended to exclude malignancy. Because malignant degeneration is very rare, close clinical and sonographic follow-up without biopsy is generally sufficient. Serial sonograms are useful to document stability or regression of tumor size during glucocorticoid replacement therapy.

Adrenal Rest Tumor↗
PubMed1984

Persisting symptoms despite permanent pacing. Incidence, causes, and follow-up.

Persisting symptoms, consisting of palpitations, dizziness, or syncope, were found in 49 of 570 consecutively followed patients (8.6 percent) with permanent pacemakers (PM). Among 540 patients with ventricular PM, 19 had syncope and 24 dizziness; among 30 patients with dual-chamber PM, five had palpitations and one dizziness. Symptoms were PM-related in 17, caused by tachyarrhythmias in 12, of noncardiac origin in 16, and of unknown origin in four patients. Holter monitoring was necessary for evaluating the persisting symptoms in 36 patients and helpful in 32 studies (89 percent). Symptoms were relieved in all patients with PM-related causes but only in 6/16 patients (38 percent) with syncope or dizziness of noncardiac origin despite various therapeutic measures. In patients with either documented tachyarrhythmias or unknown cause of syncope or dizziness, antiarrhythmic drugs led to symptomatic improvement in 11 of 12 treated patients during an average follow-up of 15 months. We concluded that: (1) persistent syncope, dizziness, or palpitations occurred in 8.6 percent of 570 patients after PM-implantation; (2) symptoms were more frequent but less severe in patients with dual-chamber PM than in those with ventricular PM; (3) tachyarrhythmias as a possible cause of symptoms were found in 25 percent of patients; (4) symptomatic improvement was noted in 28 of 29 patients when a PM-related cause or tachyarrhythmias were treated.

Adult↗
PubMed1983

Desensitization of corticotropin-releasing factor receptors.

Pretreatment of rat anterior pituitary cells with corticotropin releasing factor (CRF) rapidly and markedly reduced the ability of CRF to restimulate cyclic AMP formation and adrenocorticotropic hormone (ACTH) release. The effect was dependent on the length of time of pretreatment as well as the concentration of CRF. Neither basal nor intracellular immunoreactive ACTH levels nor basal cyclic AMP content were affected. CRF's stimulatory action on cyclic AMP formation and ACTH release recovered within one hour following CRF pretreatment. Forskolin, a compound that directly activates adenylate cyclase also releases ACTH from these cells. Pretreatment with CRF did not alter forskolin-stimulated cyclic AMP accumulation or ACTH secretion. Furthermore, CRF pretreatment did not change epinephrine's ability to increase the release of ACTH. These results indicate that CRF can regulate the responsiveness of its own receptor.

Adrenocorticotropic Hormone↗
PubMed1983

Self-improvement in a complex cybernetic system and its implications for biology.

It is commonly accepted by those who consider macroevolution as a process decoupled from microevolution that its apparent jerkiness (and, hence, incompatibility with principles of population genetics) results from the structural complexity of epigenetic systems, since all complex cybernetic systems are expected to behave discontinuously. To analyse the validity of this assumption, the process of self-improvement has been analysed in a complex cybernetic system by means of computer simulations. It turns out that the investigated system tends to develop by accumulation of as small structural changes as possible, while larger changes are likely to result in the collapse of the system rather than in its persistence or improvement. This implies that cybernetic considerations alone cannot justify the claim that the very nature of epigenetic systems induces evolution by discrete steps rather than by gradual accumulation of small changes.

Animals↗
PubMed1982

Molecular cloning and regulation of expression of the genes for initiation factor 3 and two aminoacyl-tRNA synthetases.

A 22-kilobase fragment of the Escherichia coli chromosome which contains the genes for translation initiation factor 3, phenylalanyl-tRNA synthetase, and threonyl-tRNA synthetase was cloned into plasmid pACYC184. The hybrid plasmid (designated pID1) complements a temperature-sensitive pheS lesion in E. coli NP37. pID1-transformed NP37 overproduce initiation factor 3 and phenylalanyl-tRNA synthetase. Gene expression from pID1 was studied in vitro in a coupled transcription-translation system and in minicells. The results suggest that the genes for initiation factor 3 and phenylalanyl- and threonyl-tRNA synthetase are regulated by different mechanisms.

Amino Acyl-tRNA Synthetases↗
PubMed1981

Positioning the right atrial catheter: a model for reappraisal.

A flexible Silastic casting of the human right atrium was developed to correspond to some in vivo human right atrium hemodynamic characteristics including chamber pressures, pulsatility, fluid output, and flow velocity. Using an infusion pump, air was introduced (10 ml in 30 s) into the superior vena cava of the model and aspirated via a catheter from different positions within the model atrial chamber. The tests were carried out at atrial inclinations of 60 degrees, 80 degrees, and 90 degrees from the horizontal and compared the aspiration efficiency of a single-orificed 16-gauge catheter to a 16-gauge multiorified (5 aperatures) catheter. Optimal air aspiration occurred with the multiorificed catheter tip positioned within the area 2.0 cm below the junction of the superior vena cava (SVC) and the atrial chamber at an inclination of 80 degrees. As much as 80 per cent of the incoming air could be aspirated under these conditions. At its optimal position the single-orificed catheter gave a maximal yield of 45 to 50 per cent aspiration when the tip was positioned 3.0 cm above the SVC and atrial chamber junction. Aspiration of air from mid right atrium (4.5 cm below the SVC-atrial junction) was poor regardless of the type of catheter used or atrial inclination. These data suggest a need for reappraisal of catheter design and placement.

Cardiac Catheterization↗
PubMed1981

Effect of low dose irradiation on renal enlargement in children following nephrectomy for Wilms' tumor.

The effect of low dose irradiation on subsequent compensatory renal enlargement in a group of children operated upon with unilateral nephrectomy for Wilms' tumor is reported. Comparison groups were children whose remaining kidney received either no direct irradiation or irradiation to only the upper portion of the kidney. The rate of growth of the kidney in the irradiated group was slightly less but this was not statistically significant. Thus, radiation therapy in children with Wilms' tumor, so crucial to optimum survival, does not seem to cause significant renal toxicity.

Child↗