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Biomedical subjects

R N Brown

Publications and source records attributed to R N Brown.

28 records · Page 2Linked to original sources
PubMed1991

Antigenic characterization of Psoroptes spp. (Acari: Psoroptidae) mites from different hosts.

Immunoblotting with defined antigens and antisera revealed extensive and nearly complete antigenic cross-reactivity between Psoroptes spp. mites from a bighorn sheep, a mule deer, a cow, and a rabbit. Antigenic differences were not detected between mites from the sympatric bighorn sheep and mule deer. However, minor antigenic differences between mites from the cow and rabbit suggested that these mites were distinct from each other, as well as from the mites from the bighorn sheep and mule deer. These results are consistent with earlier morphologic studies of these populations of mites and provide additional support for the hypothesis that putative populations and/or species of Psoroptes mites may not be reproductively or ecologically isolated, particularly when their hosts are sympatric.

Animals↗
PubMed1990

Comparison of the cancer risk of methylene chloride predicted from animal bioassay data with the epidemiologic evidence.

Methylene chloride has been shown to be a lung and liver carcinogen in the mouse; yet, the current epidemiologic data show no adverse health effects associated with chronic exposure to this compound. Hearne et al. have compared the results of a large mortality study on occupational exposure to methylene chloride to the human risk predictions based on the rodent bioassay to point out the inconsistency between the animal toxicologic and human epidemiologic data. The maximum number of lung and liver cancers predicted due to methylene chloride exposure based on the rodent bioassay data was 24 compared to 14 deaths from these cancers actually observed in the Hearne et al. epidemiology study. We assess the minimum risk detectable by the human study in order to calculate the upperbound potency of methylene chloride and compare it to the potency derived from the bioassay data. Results from the epidemiology study imply an upperbound potency of 1.5 x 10(-2) per ppm, compared to 1.4 x 10(-2) per ppm calculated using the most conservative analysis of the animal data. We conclude that the negative epidemiology study of Hearne et al. is not sufficiently powerful to show that the risk is inconsistent with the human risk estimated by modeling the rodent bioassay data. Specifically, the doses to which the workers were exposed, the population studied, and the latency period were not adequate to determine that the risks are outside the bounds of the risk estimates predicted by low-dose modeling of the animal data.

Air Pollutants, Occupational↗
PubMed1989

Dendritic growth of DAPI-accumulating amacrine cells in the retina of the goldfish.

The dendritic growth of amacrine cells was studied in the retina of the goldfish. Those cells that accumulated the intraocularly injected fluorescent dye 4,6-diamidino-2-phenylindole (DAPI) were compared in retinal wholemounts from small and large animals. Dendritic arbors were stained by intracellular injections of Lucifer yellow. Based upon their dendritic morphology, two types were identified, radiate and fusiform. The dendritic field areas and the number of dendritic terminals were quantitatively compared for cells in small retinas from young fish and large retinas from old fish in the region of the retina that grows by expansion. For both cell types the dendritic fields were significantly larger in the large retinas. The radiate cells had the same number of dendritic terminals in retinas of both sizes, where the fusiform cells in the large retinas had significantly more dendritic terminals than those in the small retinas. This resulted from the addition of new dendrites to the proximal arbor. These data show that with retinal expansion the pattern of dendritic growth by a amacrine cells is cell-type specific.

Animals↗
PubMed1980

Considerations in selection and management of patients undergoing valve replacement with glutaraldehyde-fixed porcine bioprotheses.

From November, 1973, through June, 1978, 428 operations in 425 patients were performed for replacement of aortic, mitral, or aortic plus mitral valves, utilizing 277 Hancock and 180 Carpentier-Edwards bioprostheses. Actuarially determined survival at 36 months was similar for all three groups and compared favorably with our experience with the Björk-Shiley prosthesis. Certain patient-related variables influencing late survival were identified by multivariate analysis and included previous operation for congenital heart disease, coronary artery bypass grafting in nonaortic valve replacement, race (black), age at operation, and New York Heart Association Functional Class. A small but definite incidence of thromboembolism occurred in all three groups, again similar to our experience with the Björk-Shiley prosthesis. Multivariate analysis identified four factors influencing risk of thromboembolism: previous cardiac operation, age, double-valve replacement, and rhythm at discharge. Valve degeneraation occurred, primarily in children and young adults. Over the medium term, the porcine bioprosthesis compared favorably with mechanical prostheses in terms of survival, function, and thromboembolism. Certain patient-related variables affecting survival may be modified by earlier surgical intervention.

Adolescent↗
PubMed1979

Routine primary repair vs two-stage repair of tetralogy of Fallot.

Fifteen of 194 patients (7.7%) with tetralogy of Fallot operated upon since January 1, 1972 under a protocol of routine primary repair despite young age died in-hospital. Most deaths were from low cardiac output. Young age and smallness of size increased the risk of operation. No deaths occurred among patients older than 4 years. High hematocrit was also a risk factor. Transannular patching has an independent effect in increasing risk. The post-repair ratio of peak pressure in the right ventricle to that in the left did not exert an independent effect. To project current risks of a two-stage approach, we determined that five of 158 patients (3.2%) died in-hospital after secondary intracardiac repair after a previous Blalock-Taussig or Waterston anastomosis between 1967--1978. Using these data and those we have published on the risk of shunting, we project that except in very small babies, the risks of hospital death of a two-stage approach are not less than those of primary repair done without a transannular patch, except when body surface area is less than about 0.35 m2. When a transannular patch is used in the primary repair, the two-stage approach is projected to be safer when the child has a body surface area of about 0.48 m2 or smaller.

Age Factors↗