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C B Bargeron

Publications and source records attributed to C B Bargeron.

At least 19 recordsLinked to original sources
PubMed2001

Epithelial damage thresholds for multiple-pulse exposures to 80 ns pulses of CO2 laser radiation.

Corneal epithelial damage thresholds for exposures to 80 ns pulses of 10.6 microm infrared radiation produced by a CO2-TEA laser were investigated. Thresholds were determined for sequences of 1, 2, 8, 32, 128, and 1,024 pulses at pulse repetition frequencies of 10 and 16 Hz. Threshold damage is correlated by an empirical power law of the form EDth = CN(-alpha) in which EDth, is the threshold radiant exposure per pulse, and N is the number of pulses. The constants C and alpha are similar for the two pulse repetition frequencies. For the combined data set, C = 2,955 J m(-2) pulse(-1) (295.5 mJ cm(-2) pulse(-1) and alpha = 0.178. This value of the constant C is within 5% of the measured damage threshold for a single 80 ns pulse exposure. Temperature calculations reveal that the maximum temperature increase on the beam axis, 10 microm beneath the anterior tear surface, resulting from the different threshold exposures is constant to within +/-10% of the mean values. This result is consistent with a critical temperature damage model. Damage threshold measurements on cooled corneas indicate that the damage mechanism indeed has a substantial thermal component.

Animals↗
PubMed2000

An automated, handheld biosensor for aflatoxin.

A new immunoaffinity fluorometric biosensor has been developed for detecting and quantifying aflatoxins, a family of potent fungi-produced carcinogens that are commonly found in a variety of agriculture products. They have also been cited as a biological agent under weapons development. The handheld, self-contained biosensor is fully automatic, highly sensitive, quick, quantitative, and requires no special storage. Approximately 100 measurements can be made before refurbishment is required, and concentrations from 0.1 parts per billion (ppb) to 50 ppb can be determined in <2 min with a 1 ml sample volume. The device operates on the principles of immunoaffinity for specificity and fluorescence for a quantitative assay. The analytic procedure is flexible so that other chemical and biological analytes could be detected with minor modifications to the current device. Advances in electro-optical components, electronics, and miniaturized fluidics were combined to produce this reliable, small, and versatile instrument.

Aflatoxins↗
PubMed1992

Cornea epithelial damage thresholds in rabbits exposed to Tm:YAG laser radiation at 2.02 microns.

We have determined exposure conditions for minimal damage to the corneal epithelium in rabbit using a continuous wave Tm: YAG laser operating in the TEM00 mode at incident powers between 80 and 450 mW. The 1/e beam diameter was 0.94 mm and exposure durations for threshold damage ranged from 4.3 to 0.08 sec. Calculated temperature increases on the beam axis 10 microns beneath the surface at the measured thresholds were essentially constant and averaged 44 degrees C. This is basically the same temperature increase found for threshold CO2 laser damage and suggests that the critical temperature damage model, which correlates CO2 laser damage, can predict damage thresholds for mid-infrared laser radiation. We also showed that reliable thresholds can be determined in freshly enucleated eyes, thus opening up the possibility of using available laser sources in laboratories not equipped and approved for animal experiments to determine damage thresholds.

Animals↗
PubMed1992

Effects of arterial compliance and non-Newtonian rheology on correlations between intimal thickness and wall shear.

A minimally diseased (mean intimal thickness = 56 microns) human aortic bifurcation was replicated in rigid and compliant flow-through casts. Both casts were perfused with physiological flow waves having the same Reynolds and unsteadiness numbers; the pulse pressure in the compliant cast produced radial strains similar to those expected from post-mortem measurements of the compliance of the original tissue. The compliant cast was perfused with a Newtonian fluid and one whose rheology was closer to that of blood. Wall shear rate histories were estimated from near-wall velocities obtained by laser Doppler velocimetry at identical sites in both casts. Intimal thickness was measured at corresponding sites in the original vessel and linear regressions were performed between these thicknesses and several normalized shear rate measures obtained from the histories. The correlations showed a positive slope--that is, the intima was thicker at sites exposed to higher shear rates--consistent with earlier results for relatively healthy vessels, but their significance was often poor. There was no significant effect of either model compliance or fluid rheology on the slopes of the correlations of intimal thickness against any normalized shear rate measure.

Aorta↗
PubMed1990

The effect of compliance on wall shear in casts of a human aortic bifurcation.

Rigid and compliant casts of a human aortic bifurcation were subjected to physiologically realistic pulsatile fluid flows. At a number of sites near the wall in the approximate median plane of the bifurcation of these models, fluid velocity was measured with a laser Doppler velocimeter, and wall motion (in the case of the compliant cast) was determined with a Reticon linescan camera. The velocity and wall motion data were combined to estimate the instantaneous shear rates at the cast wall. Analysis showed that at the outer walls the cast compliance reduced shear rates, while at the walls of the flow divider the shear rate was increased.

Aorta↗
PubMed1989

Variations in geometry and shear rate distribution in casts of human aortic bifurcations.

Shear rates measured at sites along the walls of ten casts of human aortic bifurcations are presented to provide an indication of the variability in the shear rate distribution that can occur among individuals. The geometric characteristics and flow parameters for each of the casts are also given. Much of the variability in wall shear distribution seen here results from variations in arterial geometry; variations in flow parameters can widen further the normal range of shear distributions.

Aorta, Abdominal↗
PubMed1989

Epithelial damage in rabbit corneas exposed to CO2 laser radiation.

Corneal injury thresholds are determined for conditions not previously explored for CO2 laser radiation, including multiple-pulse exposures and a systematic investigation of the effect of beam diameter on single-pulse damage thresholds. Multiple-pulse exposures from pulse trains up to 999 pulses, having pulse repetition frequencies between 1 and 100 Hz and individual pulse durations between 10(-3) and 0.5 s, were explored. Damage thresholds are discussed in terms of an approximate critical temperature model, the damage integral model and other empirical correlations. Single-pulse exposures are accurately correlated by an empirical critical temperature model in which the critical temperatures have a weak dependence on exposure duration. However, certain aspects of the single-pulse damage data led us to propose a new thermal damage model that incorporates an endothermic phase transition as the damage mechanism. This physical model accurately correlates single-pulse damage for exposures between 10(-3) and approximately 10 s.

Animals↗
PubMed1988

Effect of flow partition on wall shear in a cast of a human coronary artery.

The effect of flow partition on wall shear was determined in a cast of a human coronary artery. A laser Doppler anemometer was used to measure the time varying velocities at selected sites close to the walls of the cast. Shear rates were derived by dividing the measured velocities at each site by the perpendicular distance from measurement site to the wall. At the bifurcation of the left main coronary artery into its anterior descending and circumflex branches the shear at sites near the outer walls of the two branches was more strongly affected by the flow partition than at sites on the flow divider and near the walls of the left main coronary artery.

Blood Flow Velocity↗
PubMed1987

Correlation between wall shear and intimal thickness at a coronary artery branch.

Pulsatile velocities were measured by laser Doppler anemometry at fourteen sites near the walls of a cast of a minimally diseased human left coronary artery bifurcation. The flow wave used in the experiments was physiologically realistic. The sites selected for hemodynamic measurement were at the outer walls of the left main artery and its anterior descending and circumflex branches, and along the flow divider. The intimal and medial thicknesses at corresponding sites in the original branch were also measured. Wall shear rates were derived from the velocity data. The correlations between time-average or maximum instantaneous wall shear rate and intimal thickness had negative slopes (P less than 0.005); that is, the intima was generally thicker at sites exposed to lower shears. These results are consistent with those obtained earlier using other human arterial bifurcations.

Biomechanical Phenomena↗
PubMed1986

Shear-dependent thickening of the human arterial intima.

Hemodynamic data were obtained by laser Doppler anemometry at 163 sites in 10 flow-through casts of minimally diseased human aortic bifurcations, and the intimal thickness at each of these sites in the original vessels was measured (mean = 208 micron, range = 10-967 micron). Analysis of the results suggests that the intimal thickness at sites exposed to high shear stresses increases quickly to a modest value, growing slowly thereafter, while the thickness at sites exposed to low shears rises more slowly but, after time, reaches higher values. Thus the intima of younger vessels is thicker where shear is high, and that of older vessels is thicker where shear is low. This behavior is rationalized by a parsimonious model in which a substance from the lumen enters the wall and is catabolized or otherwise removed. The intimal permeability and removal rate both increase as the shear stress is raised. Intimal thickness is related to the amount of the substance in the wall. This model fits the experimental data with an overall standard error of estimate of 105 micron. Although the model is an extreme simplification of the actual thickening process, it shows that the observed results can be the consequence of competing shear-dependent processes.

Adult↗
PubMed1986

Sulfur and calcific keratopathy associated with retinal detachment surgery and vitrectomy.

We report an unusual case of extensive sulfur and calcium deposition in the cornea after retinal detachment surgery, vitrectomy, and use of topical sulfacetamide. There were no signs of anterior segment ischemia and intraocular silicone oil was not used. Light and electron microscopic examination and x-ray energy dispersive analysis are described. A possible mechanism for the pathogenesis of this condition is presented.

Adult↗
PubMed1986

Measurement of wall motion and wall shear in a compliant arterial cast.

Initial measurements of the time-varying wall shear rate at two sites in a compliant cast of a human aortic bifurcation are presented. The shear rates were derived from flow velocities measured by laser Doppler velocimetry (LDV) near the moving walls of the cast. To derive these shear rate values, the distance from the velocimeter sampling volume to the cast wall must be known. The time variation of this distance was obtained from LDV measurements of the velocity of the wall itself.

Aorta↗
PubMed1985

Blood staining of the cornea. Light microscopic and ultrastructural features.

Eleven blood-stained corneas were examined by light and transmission electron microscopy at intervals ranging from one month to seven years after initial staining occurred. Blood staining in each case was associated with focal loss of endothelial cells or endothelial degenerative changes and elevated intraocular pressure. Globules of erythrocytic breakdown products penetrated the discontinuous endothelium and intact Descemet's membrane. Large deposits, primarily extracellular, displaced but did not interrupt the stromal lamellae. Keratocytes in blood-stained corneas contained erythrocytic breakdown products and hemosiderin, and were remarkable for extensive degenerative changes in contrast to keratocytes in areas of cleared cornea, which contained smaller amounts of hemosiderin and were relatively normal. After one year, clearing could be seen to involve peripheral and posterior stroma, and to a lesser degree, the anterior stroma. We found no evidence to support the contention that blood-derived macrophages play a role in the clearing of erythrocyte debris. The stereotyped pattern of peripheral, posterior, and anterior stromal clearing observed seems to be consistent with diffusion of hemoglobin breakdown products out of the cornea as the primary mechanism of clearing.

Blood↗
PubMed1985

Nonquasi-steady character of pulsatile flow in human coronary arteries.

This experiment was conducted to determine if the pulsatile flow through the proximal portion of the left coronary artery system in man exhibits quasi-steady characteristics. Steady and pulsatile flows were passed through an idealized model whose dimensions were based on a vascular cast. The mean Reynolds number was 180 and the unsteadiness number was 2.7. Velocity profiles were measured by laser Doppler anemometry at several locations along diameters in the parent and both daughter channels in the neighborhood of the "left main" bifurcation. Analysis of the results along one diameter in the "left main" channel shows that unsteady flow in the larger coronary arteries may not be simulated by a series of steady flow experiments.

Biomechanical Phenomena↗
PubMed1985

Foreign body granulomas in normal ovaries.

In 100 consecutive cases in which grossly normal ovaries were removed at the time of pelvic surgery, 9% were found to contain crystalline foreign particles. An additional 9% contained cortical granulomas. In four of six cases, computer-assisted x-ray analysis of the crystalline foreign particles was successful and revealed magnesium and silicon.

Adult↗
PubMed1984

Comparison of steady and pulsatile flow near the ventral and dorsal walls of casts of human aortic bifurcations.

Steady and pulsatile flows were passed through casts of human aortic bifurcations and, by means of a laser Doppler anemometer, fluid velocities were measured at selected sites near the ventral and dorsal walls. At these sites, in the vicinity of the bifurcation, the influence of secondary flow is significant and therefore an appreciation of the phasic variation of secondary flow patterns is important. Results are presented comparing the flow direction in both steady and pulsatile flow at sites in three casts. The common features of the flow at these sites were the persistence of the flow direction during the accelerating and decelerating phases of the pulsatile cycle, and the consistently smaller angle (measured from the inlet centerline) of the pulsatile flow direction as compared to the angle of the flow direction in steady flow.

Aorta↗