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Biomedical subjects

D L Johnson

Publications and source records attributed to D L Johnson.

391 records · Page 22Linked to original sources
PubMedDate not supplied

Trauma of the ear from infrasound.

Twenty-eight chinchillas received continuous or intermittent infrasound (1, 10, 20 Hz) at 150, 160, or 170 dB SPL; there were 7 controls. Serial sections of the temporal bones were examined using light microscopy. Pathologies noted were tympanic membrane perforation, stapes subluxation, bleeding from the middle ear mucosa and tensor tympani, strial pathology, Reissner's membrane rupture, endolymphatic hydrops, saccular wall rupture, hair cell damage, and blood in the cochlear scalae. Continuous infrasound was more damaging than intermittent. Only continuous infrasound produced saccular pathology and perforations of the tympanic membrane. Of the other pathologies observed, continuous infrasound exposures produced 67% of the hair cell damage, 73% of the bleeding in the cochlear scalae, 83% of the strial pathology, and 78% of the cases of cochlear hydrops. 170-dB infrasound exposures produced the highest percentage of ears with pathologies of the three exposure intensities. As frequency increased the percentage of ears with pathologies decreased.

Animals↗
PubMedDate not supplied

Use of fluorescent probes to monitor propranolol effects on the murine splenic lymphocyte.

Recent studies indicate that propranolol suppresses the normal murine lymphocyte mitogen dose-response(1) and that propranolol has a high affinity for the beta-adrenergic binding site on the murine lymphocyte(2). Since concentrations which suppress the lymphocyte mitogen dose-response are much greater than the Kd for the binding site, it may be suggested that the suppression of the mitogen dose-response is a result of nonspecific effects of propranolol. Three fluorescent probes (1,6-diphenyl-1,3,5-hexatriene (DPH), fluorescein conjugated concanavalin A (F-Con A), and 3,3'-dithio-diisopropyl-oxacarbocyanine iodide (diS-C3-(5)) were used to investigate possible mechanisms of the nonspecific effects of propranolol on the murine splenic lymphocyte. This report presents data which suggests a possible relationship between propranolol concentrations that alter lipid membrane dynamics, as monitored by the fluorescence polarization of DPH, and suppression of the mitogen dose-response in short term cell cultures as effected by propranolol. Also reported are effects of propranolol on the relative mobility of surface membrane lectin receptors as monitored by the fluorescence polarization of F-Con A, effects of propranolol on the transmembrane potential as monitored by fluorescence emission of diS-C3-(5), and the propranolol effect on fluorescence polarization temperature-dependence of DPH and F-Con A. Studies of the effects of sotalol, alprenolol, and metoprolol are included and used for the comparison of different drug effects.

Alprenolol↗
PubMedDate not supplied

Interrelations of organism prevalence, specimen collection method, and host age, sex, and breed among 8,354 canine urinary tract infections (1969-1995).

Selected information was compiled from canine urinalyses and urine cultures conducted between January 1969 and December 1995. Eight thousand three hundred fifty-four microbial isolates (bacteria and fungi) included 4,873 isolates from females and 3,481 from males. Ten bacterial genera accounted for 96.3% of the urinary isolates, including Escherichia coli (44.1%), Staphylococcus spp. (11.6%), Proteus spp. (9.3%), Klebsiella spp. (9.1%), Enterococcus spp. (8.0%), and Streptococcus spp. (5.4%) as the 6 most common isolates in both genders of dogs. Among these 6 genera, female dogs were generally predisposed over males, although males had more urinary tract infections (UTIs) caused by Klebsiella spp. Distributions of ages at UTI diagnosis tended to be similar between genders. Infection with a single microbial species was responsible for >72% of UTIs in both genders. Among females, 40 breeds and a mixed-breed group represented 90.2% of all positive urine cultures, 88.4% of the individual dogs with UTIs. and 88.2% of the microbial isolations. Among males, these same 41 breed groups represented 87.9% of all positive urine cultures, 87.6% of the individual dogs, and 88.2% of the microbial isolations.

Age Distribution↗
PubMedDate not supplied

Effects of clasp flexure on a 4-META adhered light-polymerized composite resin.

Three specimen sets of removable partial denture claps were veneered using a composite resin with 4-META onto a 50-microns aluminum oxide air-abraded surface and flexed 0.01, 0.02, and 0.03 inches for 1,500 cycles. No veneers survived intact following 0.03-inch flexures; 58% survived 0.01-inch flexures and 44% survived 0.02-inch flexures intact. There was a significant increase in the number of veneer cracks in 0.02-inch flexed clasps compared to those flexed 0.01 inch.

Acrylic Resins↗
PubMedDate not supplied

Threshold of sensation for 60-Hz leakage current: results of a survey.

Canadian regulations have set a limit of 100 microA on leakage currents permitted to flow from patient-applied parts of an electromedical device under single-fault conditions, while international standards, such as International Electrotechnical Commission (IEC) 601-1, have set the limit of 500 microA under the same conditions. Canadian agencies have suggested that national standards for electromedical devices should harmonize with widely used international standards by increasing the leakage current limit to 500 microA. The authors investigated the question of whether 500 microA would compromise safety, or would be unpleasant or painful for the patient. A survey was conducted on the reactions of 95 adult volunteers to 60-Hz alternating currents ranging from 10 to 500 microA applied through typical ECG electrodes to determine the level at which these volunteers felt a distinctly uncomfortable or painful sensation. Results of this survey confirm that 500 microA currents are more than sufficient to induce pain in healthy adult volunteers, and that currents greater than 100 microA can evoke a definite sensation. Based on these findings, the authors recommend that the maximum allowable leakage current for patient-applied parts under single-fault conditions should not exceed 100 microA.

Adult↗
PubMedDate not supplied

A difference.

Explore the source record for details and available documents.

Goals↗
PubMedDate not supplied

Formation of precipitate in priming solutions for extracorporeal perfusion.

A precipitate observed in Hartman's solution used to prime a cardiopulmonary bypass circuit was identified as calcium carbonate. Analysis of the chemical equilibrium showed that the precipitation was caused by sodium bicarbonate added to prevent acidosis. Although this practice is acceptable for haemic primes, in which buffers and albumins will prevent precipitation, it should not be done with non-haemic primes prior to bypass.

Bicarbonates↗
PubMedDate not supplied

Survivors of medulloblastoma: implications for program planning.

A growing literature documents the deleterious effects of radiation therapy in children treated for malignant brain tumors. However, the clinical relevance of previous research has been limited by reliance on global IQ and achievement test scores. The present study of a sample of long-term survivors of medulloblastoma examined their cognitive and socioemotional functioning in depth with standardized psychologic measures. Participants' levels of intellectual functioning ranged from moderately mentally retarded to low average, with marked scatter across individual skills. Thirty-nine percent of participants had formal learning disabilities, with achievement substantially below their learning potential. In terms of specific areas of deficit, almost one half the patients tested (47%) showed considerable impairment in perceptual-motor coordination, fine-motor dexterity, attention and concentration, sequencing, and memory, particularly visual memory. More than one half of the sample (54%) was also described as displaying severe impairment in terms of maladaptive behaviors. Results are discussed in terms of the implications for special education, everyday skills, and psychosocial program development.

Adolescent↗
PubMedDate not supplied

Adaptation of the temporomandibular joint to altered mandibular function.

This pilot study describes responses of Sprague Dawley rats to mandibular retrusion. Lingually overcontoured crowns were cemented onto maxillary incisors to produce 3.5 mm of autoretrusion. Monitoring data indicate that activity was suppressed and nutritional intake was reduced. Histological evaluation of the 2-, 4-, 7-, and 59-day test specimens detected only a monocytic infiltrate response in the 4-day group.

Adaptation, Physiological↗
PubMedDate not supplied

Changes in the rabbit temporomandibular joint associated with posterior displacement of the mandible.

The purpose of this investigation was to study the changes in temporomandibular joint tissues, in particular the disc and its attachments, associated with muscle-powered continuous posterior displacement of the mandible for 33 days. After measurement of incisal relationships, food and water consumption, histologic and morphometric analysis, and radiologic data, it was determined that spatial relationships of joint tissues were altered. Mandibular retrusion leads to alteration in disc morphology and induces anterior positioning of the disc relative to the condylar head. Nutritional intake was disrupted by distal displacement crowns placed on the maxillary incisor teeth.

Analysis of Variance↗
PubMedDate not supplied

Source contribution of lead in house dust from a lead mining waste superfund site.

The relative contribution to household dust of lead particles from a mining waste superfund site and lead-based paint is investigated. Automated individual particle analysis (IPA) based on scanning electron microscopy (SEM) and X-ray energy spectroscopy (EDX) is used to develop a classification algorithm for determining lead particle source contribution in household dust vacuum bags. On a volume basis the proportion derived from the mining waste is found to be 26%, the proportion derived from a paint source is 16%, and the proportion from soil is 37%. In 15% of the lead particles identified a specific originating source could not be determined. Using a weighting method accounting for the lead concentration per particle rather than volume the contributions were similar for mining waste and paint, 21% and 23%, respectively, but the soil contribution was reduced to 8%, and the source for 29% of the lead could not be identified. These results suggested that the contribution of waste piles to the lead present in household dust is at least as important a source as paint. There is evidence to suggest that a large percentage of lead in the soil also originated from the waste piles and the overall contribution, therefore, of the waste piles may be greater than the contribution from paint.

Air Pollution, Indoor↗