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Biomedical subjects

D Geiger

Publications and source records attributed to D Geiger.

At least 55 records · Page 3Linked to original sources
PubMed1996

Corneal optical irregularity after excimer laser photorefractive keratectomy. The Summit Photorefractive Keratectomy Topography Study Group.

PURPOSE: To assess the influence of corneal surface microirregularities on objective and subjective visual performance after photorefractive keratectomy (PRK). SETTING: Multicenter clinical trial. METHODS: The alpha version of the Potential Corneal Acuity (PCA) computer program, currently under development, was used to qualitatively and quantitatively analyze the corneal surface of 176 eyes of 176 patients 1 year after PRK. Color maps of corneal surface irregularities were reviewed and quantitative values (PCA) predicting best spectacle-corrected visual acuity (BSCVA) as limited by the cornea were evaluated for associations with qualitative topography patterns, optical zone decentration, and clinical outcomes of BSCVA, uncorrected visual acuity (UCVA), subjective patient satisfaction, and a subjective glare/halo index. RESULTS: Qualitatively, corneas after PRK were generally characterized by a ring of optical irregularity at the juncture of the ablation zone and untreated cornea. Standard corneal topography maps graded as irregular after PRK had a significantly higher PCA value than those graded as regular. There was a trend toward higher PCA values with greater optical zone decentration that was not statistically significant. Actual BSCVA was identical to that which the PCA value predicted in 32% of patients and was within one Snellen line in 71%, within two lines in 89%, and within three lines in 94%. The correlation between the PCA and the glare/halo index and with subjective patient satisfaction was statistically significant. The relationship between PCA and UCVA was not significant. CONCLUSIONS: A ring of optical microirregularity of the corneal surface can appear at the juncture of the treated and untreated cornea after PRK, indicating that the optical zone edge might affect objective and subjective postoperative visual outcomes. Further understanding of corneal surface topography and refinement of the PCA program should help explain visual outcome after PRK.

Adult↗
PubMed1996

Segmental variations of in vitro mechanical properties in equine superficial digital flexor tendons.

OBJECTIVE: To determine the local variations of mechanical properties of the equine superficial digital flexor tendon (SDFT). SAMPLE POPULATION: 10 SDFT of adult horses, selected for absence of abnormality. PROCEDURE: Needles (with a dark marker at both ends) pinned perpendicularly through each tendon to delimit 7 segments. Each tendon was tested in traction until rupture; test was filmed, using an 8-mm video camera. For each image, the coordinates of the center of mass of each marker and the corresponding force were registered. The third-degree polynomial that best fits the stress-strain curve thus obtained was calculated by a least squares approximation. The modulus of elasticity (Emax) of each segment was evaluated as the maximum of the derivative of this polynomial. RESULTS: Mean rupture load of the 10 SDFT was 12,356 +/- 1,333 N. The strain at tendon rupture and Emax varied, respectively, from 8.1 +/- 1.3% and 1,002 +/- 161 MPa (sesamoidean region) to 12.5 +/- 1.7% and 1,189 +/- 63 MPa (metacarpal region). The values of the strain corresponding to Emax were remarkably similar along the SDFT (approx 5%). CONCLUSIONS: Emax appeared early homogeneous along an SDFT, although being slightly higher in the metacarpal region. The 5% strain corresponding to Emax could be the limit strain beyond which microlesions of the tendinous fibers begin to appear, this threshold being first reached during the traction test by the metacarpal segments.

Animals↗
PubMed1996

[The risk of needle-stick-injuries during abdominal closure].

A randomized study is being presented, which compares closure of laparotomy with 2 different needles (sharp: HR48, blunt: HR48PP = protect point). Handling and glove perforation rate is to be compared. 400 gloves in 100 laparotomies have been tested. Slightly more effort was reported from the surgeon to perforate the fascia with the blunt needle, but there was also a significantly lower perforation rate in the glove of his non-dominant hand. To avoid a contamination during operation the use of blunt needles has to be recommended.

Abdomen↗
PubMed1994

[Technique and significance of the Kock pouch].

The development of the continent ileostoma (Kock pouch) is delineated and its results are reviewed. Leading centers achieved continence in more than 90%. High rates of complications and relaparotomies in the early phase could be significantly reduced by technical modifications. Development of ileoanal pouch procedures have, however, confined the continent ileostomy to special indications.

Adenomatous Polyposis Coli↗
PubMed1992

[The use of Sorbsan in the treatment of the donor site of skin transplantations].

Sorbsan is a new dressing composed of alginate fibers extracted from seaweed. It is claimed to have important hydrophilic, haemostatic and biocompatible qualities. Sorbsan was used in the treatment of the donor site of split skin grafts in 52 patients operated in this department from 1988 to 1990. The patients of this series required a skin graft for various reasons as detailed below: a) skin burns in 24 cases; 2) covering of a muscle flap used in the treatment of sacral pressure sores in 15 cases; c) 13 cases of loss of substance from other various causes. Healing time averaged 16.8-13.4 and 9.3 days respectively in the three groups reported above. In 85% of cases, healing was achieved in a period variable between one and two weeks and a half, varying in accordance with patient age and general conditions. The speed of healing, particularly where thin grafts were taken, allowed multiple split skin grafts to be taken from the same donor site, facilitating the treatment of extensive skin burns. The dressing can be removed with ease with only minimal discomfort to the patient. The incidence of side effects such as itching and scar hypertrophy or pigmentation is low. We haven't noticed any allergic reaction in this series. We found the use of this dressing satisfying in the treatment of donor sites of split skin grafts, particularly in terms of patient comfort and speed or healing.

Adolescent↗
PubMed1992

Use of bioluminescence for detection of genetically engineered microorganisms released into the environment.

The persistence and movement of strain JS414 of Xanthomonas campestris pv. campestris, which was genetically engineered to bioluminesce, were monitored during a limited field introduction. Bioluminescence and traditional dilution plate counts were determined. Strain JS414 was applied to cabbage plants and surrounding soil by mist inoculation, by wound inoculation, by scattering infested debris among plants, and by incorporating bacteria into the soil. Bioluminescent X. campestris pv. campestris was detected in plant samples and in the rhizosphere up to 6 weeks after inoculation. Movement to uninoculated plants was detected on one occasion, but movement from the immediate release area was not detected. Strain JS414 was detected in soil samples beneath mist- and wound-inoculated plants only at intentionally infested locations and in aerial samples only on the day of inoculation. Our bioluminescence methods proved to be as sensitive as plating methods for detecting the genetically engineered microorganisms in environmental samples. Our results demonstrate that transgenic incorporation of the luxCDABE operon provides a non-labor-intensive, sensitive detection method for monitoring genetically engineered microorganisms in nature.

Containment of Biohazards↗
PubMed1992

[Lift mask with use of a malleable implant: BOP S.P. Initial results].

The mask lift, the latest technique for facial rejuvenation, comprises a large remodelling of the frontal and orbito-malar area. The modelling resections by bone-grinding are essentially designed to taise the superior orbital rim, but by the onlay grafts on the malar bone as well as the ones on the superior orbital rim many problems occur due to the donor site (autogenous bone), their biocompatibility and eventual resorption or integration. It is therefore proposed to use BOP S.P. as an onlay graft, a synthetic and biocompatible material already used in neurosurgery for cranioplasties with good results. Its essential advantage over other implants is its wax like consistency and its progressive adhesion to the bone, which allows onlay grafts to be placed wherever required; the modelling is fast, the result are immediately controllable and it is stable after a few hours hardening. BOP S.P. is essentially used as onlay graft material for mask lifts, but has also been successfully tested on 4 facial contour reconstructions for corrections after major traumatic injuries. No complication has been observed in a series of 9 cases but a one year follow-up is too short.

Biocompatible Materials↗
PubMed1989

Potassium depletion and hypertonic medium reduce "non-coated" and clathrin-coated pit formation, as well as endocytosis through these two gates.

Intracellular potassium depletion inhibits receptor-mediated endocytotic processes occurring through clathrin-coated pits. Besides the clathrin-coated pit route, flask-shaped invaginations that do not bear a typical clathrin coat have been recently implicated in receptor-mediated endocytosis of cholera toxin. These invaginations are called "non-coated" to distinguish them from the typical clathrin-coated pits. In the present study, we have investigated whether "non-coated" invaginations are sensitive, as are clathrin-coated pits, to potassium depletion and whether hypertonic medium, which inhibits receptor-mediated endocytosis, also affects "non-coated" invaginations. We found that 1) both potassium depletion and hypertonic medium reduce "non-coated" invaginations on the cell surface; 2) similar to potassium depletion, hypertonic medium markedly decreases the number of clathrin-coated pits; 3) these changes are accompanied by an inhibition of the internalization (measured morphologically) of cholera toxin-gold through "non-coated" invaginations, as well as of alpha 2-macroglobulin-gold taken up by clathrin-coated pits; and 4) in addition, both the hypertonic medium and potassium depletion inhibit the uptake of horseradish peroxidase, a marker of fluid-phase endocytosis.

Animals↗
PubMed1989

Stereo and eye movement.

We describe a method to solve stereo correspondence using controlled eye (or camera) movements. Eye movements supply additional image frames and monocular depth estimate, which can be used to constrain stereo matching. Because the eye movements are small, traditional stereo techniques of stereo with multiple frame will not work. We develop an alternative approach using a systematic analysis to define a probability distribution for the errors. Our matching strategy then matches the most probable points first, thereby reducing the ambiguity for the remaining matches. We demonstrate this algorithms with several examples.

Computer Simulation↗
PubMed1989

Down-regulation of insulin receptors is related to insulin internalization.

In the present study, we have tested the influence of inhibition of endocytosis by hypertonic medium on the regulation of cell surface insulin receptors. We show that active internalization of 125I-insulin is markedly inhibited by hypertonic media and that, in parallel, cell surface invaginations are significantly diminished. These two events are accompanied by a marked inhibition of cell surface insulin receptor down-regulation. These data provide further strong evidence that receptor-mediated endocytosis is the major mechanism by which insulin receptors are regulated at the surface of target cells.

Cell Line↗
PubMed1989

Receptor-mediated endocytosis of insulin: inhibition of [125I]iodoinsulin internalization in insulin resistant diabetic states of man.

We have used electron microscopic autoradiography to quantitatively study receptor-mediated endocytosis of [125I]insulin in freshly isolated monocytes from patients with non-insulin-dependent diabetes mellitus. In obese, non-obese, and lipoatrophic patients with diabetes, internalization of [125I]insulin was impaired at 30 min of incubation at 37 degrees C. By 60 min of incubation, however, internalization was indistinguishable from that of normals. In obese non-diabetic controls, internalization at 30 min was slightly less than internalization in normals but greater than that of the diabetic group. Dieting was associated with normalization of internalization in the obese group. We conclude that the rate of [125I]insulin internalization is impaired in non-insulin-dependent diabetes and compare this to previously reported results in insulin-dependent diabetes mellitus.

Adult↗
PubMed1986

Intracellular potassium depletion in IM-9 lymphocytes suppresses the slowly dissociating component of human growth hormone binding and the down-regulation of its receptors but does not affect insulin receptors.

We have investigated whether the slowly dissociating component of insulin and human growth hormone (hGH) binding and the homologous down-regulation of their receptors in IM-9 cultured human lymphocytes are due to distinct conformations of the receptor or, rather, to a redistribution within the cell. To do so, we used intracellular K+ depletion, which has been shown to inhibit reversibly coated-pit formation and ligand internalization in some cell lines. IM-9 cells incubated in K+-free buffer after a hypotonic shock rapidly lost their K+, which was stabilized at +/- 50% of control by incubation in K+-free binding assay buffer. In K+-depleted cells, the hGH dissociation kinetics became monoexponential and, in contrast with control cells, compatible with the equilibrium constant derived from saturation and association data using a simple model. The loss of hGH receptors during competition studies was abolished. The down-regulation by unlabeled hGH was decreased by 80%. In contrast, insulin receptor kinetics remained unchanged (non-first-order) in the K+-depleted cells; the negative cooperativity and the down-regulation (60%) were identical to those of control cells. Quantitative electron microscopic autoradiography showed a decrease of +/- 50% in the fraction of 125I-labeled hGH internalized. The number of visible coated pits in the membrane was reduced by 80%. Thus, in IM-9 cells, association with coated pits and endocytosis appear to play a major role in the kinetics of hGH binding and in the down-regulation of its receptors, but not in insulin-receptor binding kinetics and down-regulation.

Cell Line↗
PubMed1986

Survey of genetic authenticity of commercially produced inbred rats.

Strain specific typing antisera (SSTA) were used to genetically monitor six inbred strains of rats from major US commercial producers. SSTA were used in both the hemagglutination test and the microcytotoxicity assay because results from a preliminary study showed that use of both tests gave more reliable results than either test used individually. Of 25 colonies tested (representing all six strains), one colony of LEW rats appeared to be contaminated genetically.

Animals↗
PubMed1985

Carbon-PGLA prostheses for ligament reconstruction. Experimental basis and short-term results in man.

The efficiency of a pure carbon prosthesis to reconstruct intra-articular ligamentous loss of substance was evaluated on 14 sheep with an 18-month follow-up study of recent and old ACL experimental injuries. Functional results showed a correlation between a tightened implant, the stability of the knee, and the absence of severe arthritis. The rupture strength of the newly formed ligament amounts to about 300 Newtons (N). That of the normal ACL amounts to 250-550 N. The structure gives a viscoelastic behavior to the prosthesis. This tissue was made of collagen fibers surrounding the carbon fibers and running generally in the direction of the ligament. In the osseous tunnels, the newly formed lamellar bone invaded and surrounded the implant. Carbon fiber fragmentation occurred, and fibers were found in the synovia and in the homolateral, inguinal, and paraaortic lymph nodes. No degeneration, necrosis of tissue, or cellular toxicity was found. On these bases, the carbon prosthesis was modified by adding a resorbable copolymer of polyglycollic (PGA) and polylactic acid (PLA) around the fibers and a resorbable sheath of the same polymer. This carbon-PGA/PLA prosthesis was used in 23 patients with a three- to 12-month follow-up period. Patients were evaluated by clinical tests and by functional control of the ligament. The indications for prosthetic replacement were: recent mop-end tears of the ACL, cruciate ligament reconstruction in chronic knee instability, and wide rotator cuff loss of substance. Five complications occurred because of hematomas and/or sepsis and prosthesis breakage. Eighteen of 23 patients had good clinical results with good function in five. The conclusions are that PGA/PLA produces a clean and flexible ligament, thus eliminating carbon fiber articular deposits and allowing a normal function. Inflammatory postoperative reactions seem to be more frequent than with other procedures and call for operative and clinical care in order to eliminate hematoma and sepsis. The efficiency of a rehabitable carbon-PGA/PLA prosthesis in intra-articular ligamentous defects in man will be confirmed only by controlled long-term clinical observations.

Adult↗
PubMed1984

Harmonic and impulse rheological tests of biomaterials.

Up to now, not so much attention has been paid concerning the dynamic rheological behaviour of soft tissues although non linear viscoelastic effects have often been reported when mechanical properties of biomaterials are concerned. In order to characterize such properties different rheological tests have been proposed, the two principal being the study of the sample stresses responses to applied strains which are either harmonic with time or of step function type. Two different apparatus have been designed in our laboratory which allow specific rheological tests on biological materials under controlled environmental conditions. With one of them, harmonic uniaxial extension tests are performed in a large domain of frequencies (.001 Hz to 100 Hz) and forces (up to 20 daN); with the other, the samples are submitted to relaxation tests in uniaxial elongation up to 5 cm deformation within time duration of the order of 20 ms. The principal characteristics, limitations and performances of such apparatus are presented and few examples of data thus obtained are given. On the basis of quasi linear viscoelasticity models, it can be shown that both two types of tests with their proper limitations are leading to the same rheological parameters.

Biocompatible Materials↗