Biomedical subjects

A Bachmann

Publications and source records attributed to A Bachmann.

13 recordsLinked to original sources

PubMed1991

Relative biochemical reactivity of three hexachlorocyclohexane isomers.

The rate and mechanisms of degradation of three hexachlorocyclohexane (HCH) isomers were studied with rat liver cytochrome P450, which is known to react with chlorinated compounds in the presence and absence of molecular oxygen. In addition, P450 is produced from HCH metabolites which are found aerobically and anaerobically during microbial biodegradation of this compound in a complex soil system. Conversion assays with P450 were carried out with alpha-, beta-, and gamma-HCH. Hexachloroethane served as a reference compound for bioconversion kinetics. Under anaerobic conditions, gamma-HCH was readily dechlorinated (r0 = 0.31 nmol/min.nmol cyt.P450) to tetrachlorocyclohexene and monochlorobenzene. gamma-HCH was also reductively dechlorinated, but at a much slower rate (r0 = 0.03 nmol/min.nmol cyt.P450). Both substrates followed Michaelis-Menten kinetics (gamma-HCH: Vmax = 1.87 nmol/min.mg and Km = 47 mumol/liter; gamma-HCH: Vmax = 0.24 nmol/min.mg and Km = 201 mumol/liter). Under aerobic conditions, bioconversions of gamma-HCH (r0 = 0.05 nmol/min.nmol cyt. P450) and alpha-HCH (r0 smaller than detection limit) were slower. beta-HCH proved to be recalcitrant under both aerobic and anaerobic conditions. The differences in bioconversion rates between the three HCH isomers could be related to the differences in spatial chlorine configuration of the three isomers. beta-HCH recalcitrance was explained by the absence of axial-orientated chlorines.

Aerobiosis↗

PubMed1988

Biodegradation of alpha- and beta-hexachlorocyclohexane in a soil slurry under different redox conditions.

Aerobic conditions proved to be best for the microbiol conversion of alpha-hexachlorocyclohexane (alpha-HCH) in a soil slurry. The dry soil contained 400 mg of alpha-HCH per kg. This xenobiotic compound was mineralized within about 18 days at an initial rate of 23 mg/kg of soil per day by the mixed native microbial population of the soil. The only intermediate that was detected during breakdown was pentachlorocyclohexene, which was detected at very small concentrations. Alpha-HCH was also bioconverted under methanogenic conditions. However, a rather long acclimation period (about 30 days) was necessary before degradation started, at a rate of 13 mg/kg of soil per day. Mass balance calculations showed that about 85% of the initial alpha-HCH that was present was converted to monochlorobenzene, 3,5-dichlorophenol, and a trichlorophenol isomer, possibly 2,4,5-trichlorophenol. Under both denitrifying and sulfate-reducing conditions, no significant bioconversion of alpha-HCH was observed. The beta isomer of HCH was recalcitrant at all of the four redox conditions studied. We propose that the specific spatial chloride arrangement of the beta isomer is responsible for its stability. The results reported here with complex soil slurry systems showed that alpha-HCH is, in contrast to the existing data in the literature, best degraded biologically in the presence of oxygen.

Aerobiosis↗

PubMed1988

Aerobic biomineralization of alpha-hexachlorocyclohexane in contaminated soil.

The factors identified to be important for the aerobic biodegradation of alpha-hexachlorocyclohexane (alpha-HCH) in a soil slurry are temperature, auxiliary carbon source, substrate concentration, and soil inhomogeneities. Temperatures in the range of 20 to 30 degrees C were determined to be most favorable for biodegradation of alpha-HCH. No alpha-HCH biodegradation was detected at temperatures below 4 degrees C and above 40 degrees C. The addition of auxiliary organic carbon compounds showed repressive effects on alpha-HCH biomineralization. Increased oxygen partial pressures reduced the repressive effects of added auxiliary organic carbon compounds. A linear relationship between alpha-HCH concentration and its conversion rate was found in a Lineweaver-Burk plot. Inhomogeneities such as clumping of alpha-HCH significantly affected its biodegradation. Inhomogeneity as an influence on biodegradation has not drawn sufficient attention in the past, even though it certainly has affected both laboratory studies and the application of biotechnological methods to clean up contaminated sites. On the basis of metabolites detected during degradation experiments, the initial steps of aerobic alpha-HCH bioconversion in a soil slurry are proposed.

Bacteria, Aerobic↗

PubMed1986

[A new device for the metric study of the hard palate].

This new device which measures anatomic elevations makes it possible that the measurements on the palate model can be performed very rapidly. This permits outstanding exact classification of the palate relief to the respective category.

Anthropology, Physical↗

PubMed1985

The percentage of projection neurons and interneurons in the human lateral geniculate nucleus.

Projection neurons and local circuit neurons of the human lateral geniculate nucleus (LGN) offer different patterns of lipofuscin pigmentation. One type of projection cell (type I neuron) and two varieties of local circuit neurons (type II and type III neurons) can be distinguished on account of their characteristic pigmentation. The majority of the nerve cells are type I projection neurons. Pigmented type II neurons comprise about 8.5% and type III neurons devoid of pigment amount to only 0.2% of the nerve cells.

Aged↗

PubMed1979

Mucogingival surgery. The subperiosteal vestibule extension. Clinical results 2 years after surgery.

A surgical technique to establish wide zones of attached mucosa was performed in 28 patients presenting with inadequate amounts of attached gingiva. The clinical results of the procedure were monitored over a period of 2 years. Biometric assessment of 112 mucogingival units immediately before and at 1, 3, 6, and 24 months after surgery revealed that the mean width of attached gingiva changed from 1.1 mm to 5.3 mm of attached tissue (gingiva plus vestibular mucosa). A surgically produced increase of 4.9 mm in width (P less than 0.001) and subsequent shrinkage of 0.7 mm or 14% (P less than 0.001) resulted in a total average gain of 4.2 mm of attached mucosa 2 years after surgery (P less than 0.001). A begin/end analysis of the coronal level of clinical periodontal attachment and the extent of gingival recession showed no clinically significant changes. The mean width of keratinized gingiva increased 0.8 mm during the 2-year postoperative period. The subperiosteal vestibule extension is recommended as an alternative to the free autogenous mucosa graft for establishing wide bands of attached mucosa in areas where loss of attached gingiva is associated with mechanical or microbial irritation of the marginal periodontium.

Adolescent↗

PubMed1979

[The use of alpha-chymotrypsin in traumatology].

Due to its fibrinolytic activity, alpha-chymotrypsin should be applied, even in doses of 5 and 10 mg (as indicated in the List of Drugs) only for postoperative oedema and haematoma prophylaxis, with due regard to the simultaneous effect on haemostasis. The maximum of fibrinolytic activity was observed 6 to 9 hours after intramuscular injection. These findings are consistent with clinical observation. The authors dissuade from uncontrolled use because, in spite of many separate experimental studies and clinical trials, there are still numerous questions that must be considered unsettled.

Adult↗

PubMed1976

[Cracks in the dental enamel caused by sensitivity testing with CO2 snow and dichloro-difluoromethane--a comparative in vivo study].

With the aid of permeating dye and standardized fluorescence UV-photography, the reaction of subjects and enamel to the application of two pulp vitality testing methods (frozen carbon dioxide and Frigen -pellets) was examined. The enamel lamella system, the diffusion of temperature changes through the tooth crown and the thermodynamic pattern of enamel and dentine are described in detail. Structural changes of enamel as well as the subject's reaction times to a cold stimulus during the vitality tests are documented and the data are compared. Frigen caused less enamel changes than did frozen carbon dioxide. The subject's reaction times were similar for both methods. There were no differences between the methods with regard to the number of reopened, extended and newly created enamel fissures. However, the length, width and depth of these fissures proved to be less pronounced for Frigen than for carbon dioxide. Clinical implications of the results are discussed.

Cold Temperature↗

PubMed1973