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Biomedical subjects

A Vogel

Publications and source records attributed to A Vogel.

At least 109 records · Page 6Linked to original sources
PubMed1986

Cavitation bubble dynamics and acoustic transient generation in ocular surgery with pulsed neodymium: YAG lasers.

The authors have investigated the application of mode-locked and Q-switched Neodymium:YAG (Nd:YAG) lasers in ocular surgery by means of high-speed photography and hydrophone measurements. The incisive effect relies on the optical breakdown at the laser focus. Cavitation bubbles and acoustic transients are thereby generated. Their size and pressure amplitude have been measured at various laser-pulse energies. With a pulse energy of 5 mJ, the bubble is 1.5 to 2.3 mm in diameter and the pressure of the acoustic transient is 9 to 16 bar (130 to 230 psi) at a distance of 18 mm from the focal point. Bubble size and amplitude of the pressure pulse are always approximately 50% higher with a Q-switched laser than with a mode-locked laser. However, the size of the ruptures produced in a polyethylene membrane by the laser pulses is the same for both modes of operation. The energy balance shows that not only mechanical effects, but also thermal mechanisms are responsible for photodisruption.

Acoustics↗
PubMed1986

[Cavitation bubble dynamics and shock wave generation in eye surgery using the pulsed neodymium:YAG laser].

In a model experiment using polyethylene membrane in balanced salt solution the processes which take place during posterior capsulotomy with pulsed Nd:YAG lasers were investigated by means of high-speed photography and hydrophone measurements. It was found that cavitation bubbles with a maximum diameter of 1.5 to 2.3 mm develop at the focal point even with a pulse energy of 5 mJ; i.e., their spatial extent is much greater than that of the ruptures observed. Furthermore, during optical breakthrough and when the bubble collapses shock waves are generated with a pressure amplitude of 9 to 16 bat at a distance of 18 mm or 162 to 288 bar at 1 mm. Previous estimates ranged from more than 0.1 bat at 15 mm to several kilobar at 1 mm. Above a certain threshold value the energy of the cavitation bubble and of the shock waves is approximately proportional to the energy of the laser pulses with which they are generated. At the same time pulse energy the diameter of the bubbles generated by Q-switched lasers is around 1.5 times as large as those generated by model-locked lasers--the bubble energies are more than three times as great. The shock wave amplitudes after O-switched pulses are likewise 1.5 times as great as after mode-locked pulses and the energy of the shock waves is approximately double. Nevertheless, the size of the holes caused in a polyethylene membrane with a pulse energy of 2 mJ to 5 mJ does not depend on the laser operating mode. Thus, with the polyethylene membrane, no great correlation was found between the mechanical energy acting on it and the size of the holes thus created.(ABSTRACT TRUNCATED AT 250 WORDS)

Cataract Extraction↗
PubMed1985

Inhibitors of retroviral DNA polymerase: their implication in the treatment of AIDS.

Compared to other T-lymphotropic human retroviruses, human T-cell leukemia (lymphotropic) virus I (HTLV-I) and HTLV-II, the acquired immunodeficiency syndrome (AIDS)-associated virus, HTLV-III, is a nontransforming cytopathic virus without immortalizing activity. Thus the virus replication is an important event in the manifestation of this disease, and the interruption of viral replication offers an important strategy for the control of AIDS. For this reason we have purified the reverse transcriptase (RT) from HTLV-III and from HTLV-III infected cells to study the structure-activity relationship of RT inhibitors developed in our laboratory. The cellular DNA polymerases from H9 cells were also purified to study the selectivity of RT inhibitors. Purified HTLV-III RT has several distinguishing features: (a) unlike the HTLV-I enzyme it is highly stable and can be kept for several weeks without any loss of activity; (b) using identical procedures of isolation the HTLV-III enzyme shows a much higher activity than does the enzyme from HTLV-I; (c) the Vmax for HTLV-III RT is by severalfold higher than that for the HTLV-I enzyme in the presence of (rC)n X (dG)12 and (rCm)n X (dG)12, and besides the usual template-primers used for RT assay this enzyme has a relatively high affinity for (rAm)n X (dT)12; and (d) the cationic requirements for the transcription of various template-primers are unusual. The purified enzyme has a molecular weight of 95,000-98,000, as judged by the gel filtration method. The purified HTLV-III RT was inhibited by a partially thiolated polycytidylic acid (5-mercaptopolycytidylic acid); the cellular DNA polymerase beta from H9 cells was not sensitive to 5-mercaptopolycytidylic acid. Germanin (synonym, suramin), an antiprotozoan drug, also inhibits HTLV-III RT activity, but the DNA polymerase alpha activity was also sensitive to Germanin. The nonspecific effect of Germanin is probably due to the high content of sulfonic acid residues. This paper describes new approaches for designing specific inhibitors of retroviral reverse transcriptases which may be useful in developing a potential drug against AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1985

[Clinical aspects and genetics of pseudoxanthoma elasticum].

Eighteen cases of Pseudoxantoma elasticum (PXE) were analysed using clinical and genetic criteria. We observed great intra- and interfamiliar variations in the manifestations of the disease as well as mono-, bi- and trisymptomatic cases (skin + eyes + vessels). We lack reliable indications for the existence of more than one recessive type of PXE and hence for heterogeneity. In family 9, PXE was inherited in an autosomal-dominant mode, and the discrete symptoms were restricted to the skin.

Aged↗
PubMed1985

[Light and electron microscopy of pseudoxanthoma elasticum].

Five patients with recessive pseudoxanthoma elasticum (PXE-R) and four with dominant transmission of the disease (PXE-D) belonging to the same family were studied by light and electron microscopy. In PXE-R, calcification in the elastic fibres causes their enlargement, excavation and fragmentation. On the other hand, in PXE-D irregularly shaped and unevenly lined elastic strands may form an anastomotic wickerwork intimately intermingled with the collagenous texture. In other places, elastic bundles seem to be composed of very tiny elements. Both aspects represent a dysplasia of the elastic tissue. Independently of the mode of inheritance, a variable proportion of enlarged collagen fibrils exhibit a "flower-like" structure. Additionally, in PXE-D alone a peculiar aggregation of small and large collagen fibrils is observed. Granulofilamentous material mixed with tiny collagen fibrils is found in both groups of patients. On the basis of our observations, PXE-R and PXE-D may be identified by light and electron microscopy.

Collagen↗
PubMed1985

[Changes in the fine structure of the masseter muscle as affected by unilateral occlusal disorders].

Biopsy specimens from the masseter muscle of the miniature pig "Mini-LEWE" were analysed histochemically before and after unilateral occlusal disturbances. The percentages of different fibre types and the cross-sectional area of fibres were determined with the myosin-ATPase reaction after acid preincubation. The capillary membranes were visualized by means of modified PAS-reaction. There was demonstrated a significant increase from the percentage portion of ST-fibre types, especially of the side of occlusal disturbance, under experimental conditions. This indicates an increased isometric contraction of the masseter muscle. The size of FT-fibre types and the capillarity increase significantly on the side without occlusal disturbances, due to the dislocation of the masticatory efforts to this side. The masseter muscle fine structure is shown to be adapted good to the disturbed functional conditions. No significant side differences were found in the dry mass of the masticatory muscles, at the end of experiments.

Animals↗
PubMed1984

Cysteine in the triple-helical domain of one allelic product of the alpha 1(I) gene of type I collagen produces a lethal form of osteogenesis imperfecta.

We studied tissue and cultured skin fibroblasts from a newborn with the lethal perinatal form of osteogenesis imperfecta born to a mother with the Marfan syndrome and her unrelated husband. Dermis from the infant was thinner and fibril diameter smaller than control; dermal fibroblastic cells had dilated endoplasmic reticulum. His fibroblasts in culture synthesized two different species of pro alpha 1(I) chains in about equal quantity. One chain was normal, the other contained cysteine within the triple-helical portion of the COOH-terminal cyanogen bromide peptide alpha 1(I)CB6. Molecules which contained two copies of the mutant chain formed alpha 1(I)-dimers linked through interchain disulfide bonds. Molecules which contained either one or two mutant chains were delayed in secretion and underwent excessive lysyl hydroxylation and hydroxylysyl glycosylation of all chains in the molecule, probably as a result of delayed triple-helix formation. Molecules containing either one or two copies of the mutant chain melted at 38 degrees C instead of 41 degrees C. The most likely explanation for these findings is that a cysteine is substituted for a glycine in the triple-helical domain of the products of one of the alpha 1(I) alleles. Such a substitution would interfere with triple-helix formation and stability and thus explain 1) the decreased melting temperature, 2) the increased post-translational modification, 3) the altered rate of secretion and accumulation of intracellular material, 4) the increased intracellular degradation of newly synthesized collagen, and 5) the decreased collagen production. Since neither parental cell strain produced the same mutant chain, the findings are best explained by a new mutation in one of the alpha 1(I) genes. The role of the uncharacterized "Marfan" gene in modifying the phenotype in this patient is unclear.

Alleles↗
PubMed1984

Production of platelet-derived growth factor-like molecules and reduced expression of platelet-derived growth factor receptors accompany transformation by a wide spectrum of agents.

A series of nontransformed human and murine cells and derivative cell lines transformed by methylcholanthrene; by simian virus 40, Kirsten and Moloney murine sarcoma viruses, simian sarcoma virus, and adenovirus; and by a "spontaneous" event in culture were examined for the expression of receptors for the platelet-derived growth factor (PDGF) and for production of substances able to compete with 125I-labeled PDGF for binding to the cell-surface PDGF receptor. In each case, transformation resulted in a 50-100% decrease in available PDGF receptors. All transformed cells except the methylcholanthrene-transformed mouse cells produce a PDGF competitor into the conditioned medium. Levels of PDGF competitor in conditioned medium at the end of a 48-hr collection were as high as 2 ng/ml--high enough to be measured by radioreceptor assay diluted 1:30 and to maximally stimulate [3H]thymidine incorporation by human fibroblasts. The PDGF competitor activity detected in a radioreceptor assay does not reflect irreversible (e.g., proteolytic) damage to the receptor of test cells since its effects are reversed by acetic acid dissociation. Antiserum against human PDGF neutralizes 20-80% of the PDGF competitor found in conditioned medium from different transformed human cells and 100% of the activity from normal human endothelial cells. The possibility that induction of expression of the cellular PDGF gene may be involved in the mechanism of transformation of PDGF-responsive mesenchymal cells is discussed.

Animals↗