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Biomedical subjects

M K Schmehl

Publications and source records attributed to M K Schmehl.

14 recordsLinked to original sources
PubMed1993

Effects of antibiotics on the endothelium of fresh and cryopreserved canine saphenous veins.

To determine if antibiotic solutions for potential use in antimicrobial treatment of tissues were detrimental to cell viability, canine saphenous veins were exposed to three different antibiotic solutions at 37 degrees C for 12 h. Viability was determined by tissue culture, utilizing a limiting dilution assay. The antibiotic series included two formulations currently used for the preservation of heart valves and a new formulation containing imipenem, a broad spectrum beta-lactam. Currently used antibiotic regimes and imipenem with gentamicin resulted in a decrease of 30 to 50% of the viable endothelial cells within 12 h. Exposure of the saphenous veins to imipenem or imipenem combined with amphotericin B had no adverse effects on the viability of the endothelial cells with 12 h exposure. However, veins exposed to amphotericin B were more susceptible to subsequent damage during freezing and thawing than veins frozen after incubation with either imipenem alone or imipenem combined with flucytosine. These studies indicate that imipenem combined with flucytosine is suitable for use with vein grafts.

Animals↗
PubMed1991

Transplantation of cryopreserved canine venous allografts.

Local vascular reconstructions frequently require the use of vein grafts to bridge arterial or venous defects. Most previous studies on the use of cryopreserved veins have used relatively large caliber vessels. There have been few studies on the effectiveness of cryopreserved micro- or small-venous allografts. Here, we tested two types of cryopreserved venous allografts: (1) 1.5- to 1.9-mm diameter microvenous grafts (MVG); and (2) 4- to 5-mm diameter small venous grafts (SVG). Cryopreserved MVG allografts were placed into saphenous arteries of six experimental dogs and SVG cryopreserved allografts were placed into femoral arteries of six experimental dogs for 3 to 6 weeks. Two fresh MVG autografts were also transplanted into experimental dogs as controls and autografts were transferred to the contralateral side in SVG dogs as controls. None of the six cryopreserved MVG grafts retained patency but three/six cryopreserved SVG allografts were patent at harvest. Histological examination of grfts revealed control autografts were undergoing arterialization with an intact intima. Experimental cryopreserved allografts showed extensive medial fibrosis, significant lymphocytic infiltrates, and sporadic areas of intact intima for both patent and nonpatent grafts.

Animals↗
PubMed1990

Thermographic studies of phantom and canine kidneys thawed by microwave radiation.

Whole organs, such as kidneys, must be thawed quickly and uniformly to prevent damage during thawing due to excessive heating. Electromagnetic heating with microwaves thaws the kidneys quickly but frequently produces "hot spots" with heat damage. To study heat damage, phantom gelatin kidneys with different dielectric constants and canine kidneys perfused with 12.5% glycerol, ethylene glycol, or dimethyl sulfoxide before freezing were microwave thawed, and the interior temperature was measured by thermography. Phantom kidneys were thawed free standing and canine kidneys were either free standing or packed in a gel mixture. Both phantom and canine kidneys were split symmetrically and separated with a sheet of Styrofoam to facilitate immediate separation and evaluation of the halves after thawing (approximately 3 sec). All the phantoms, regardless of dielectric properties, had areas less than 0 degrees C or greater than 37 degrees C after thawing. The free-standing canine kidneys and the gel-packed ethylene glycol-perfused kidneys had frozen areas (less than 0 degrees C) and hot spots (greater than 37 degrees C). However, glycerol- and dimethyl sulfoxide-perfused kidneys packed in gel before thawing had no areas less than 0 degrees C or greater than 37 degrees C. Altering the geometry from a "kidney shape" to a cylindrical shape with increased volume improved the uniformity of thawing and was more effective than altering the dielectric constant over the range evaluated.

Animals↗
PubMed1990

Bactericidal effectiveness of modulated UV light.

Studies were designed to evaluate the effectiveness of pulsed modulated UV light waveforms for killing bacteria. Exposure of five strains of bacteria to the modulated information encoded in the light decreased the colony population from a confluent lawn to less than 20 colonies. However, approximately 2,000 colonies survived treatment with the same intensity and time of exposure to UV light lacking the modulated information.

Bacteria↗
PubMed1989

Power analysis of statistical methods for comparing treatment differences from limiting dilution assays.

Six different statistical methods for comparing limiting dilution assays were evaluated, using both real data and a power analysis of simulated data. Simulated data consisted of a series of 12 dilutions for two treatment groups with 24 cultures per dilution and 1,000 independent replications of each experiment. Data within each replication were generated by Monte Carlo simulation, based on a probability model of the experiment. Analyses of the simulated data revealed that the type I error rates for the six methods differed substantially, with only likelihood ratio and Taswell's weighted mean methods approximating the nominal 5% significance level. Of the six methods, likelihood ratio and Taswell's minimum Chi-square exhibited the best power (least probability of type II errors). Taswell's weighted mean test yielded acceptable type I and type II error rates, whereas the regression method was judged unacceptable for scientific work.

Cell Survival↗
PubMed1989

Comparison of statistical methods for the analysis of limiting dilution assays.

This study reports the results of a critical comparison of five statistical methods for estimating the density of viable cells in a limiting dilution assay (LDA). Artificial data were generated using Monte Carlo simulation. The performance of each statistical method was examined with respect to the accuracy of its estimator and, most importantly, the accuracy of its associated estimated standard error (SE). The regression method was found to perform at a level that is unacceptable for scientific research, due primarily to gross underestimation of the SE. The maximum likelihood method exhibited the best overall performance. A corrected version of Taswell's weighted-mean method, which provides the best performance among all noniterative methods examined, is also presented.

Cell Survival↗
PubMed1989

Parameters for evaluation of viability assays: accuracy, precision, specificity, sensitivity, and standardization.

The selection of appropriate viability assays is critical in evaluating the efficacy of any cryopreservation procedure. The appropriateness of a given assay depends on the specific tissue and the function which is being optimized. Although a broad range of "viability" assays have been used, these assays can be classified in seven principle groups: (i) Morphological procedures, including routine histology, surface antigen localization, and transmission electron or scanning microscopy; (ii) proliferation studies; (iii) metabolic assays; (iv) implantation; (v) mechanical assays; (vi) motility; and (vii) DNA or RNA synthetic assays. Regardless of the class of assay, each assay may be further characterized as qualitative, quantitative, or quantal and each type may vary in the degree of subjectivity. In selecting a specific viability assay, biological variability, assay bias, and the statistical probability of both Type I and Type II errors should be considered crucial. Here we discuss a number of critical factors involved in validating viability assays, including accuracy, precision, standardization, specificity, sensitivity, selection of statistical methodology, and range of the assay.

Animals↗
PubMed1987

Comparative ultrastructure of the zona radiata from eggs of six species of salmonids.

The zona radiata from unactivated and activated eggs from chinook salmon (Oncorhynchus tshawytscha), chum salmon (O. kisutch), pink salmon (O. gorbuscha), brown trout (Salmo trutta), rainbow trout (S. gairdneri) and lake trout (Salvelinus namaycush) were examined using scanning and transmission microscopy. The zona radiata in all species examined consisted of an outer adhesive coating, a thin densely staining zona radiata externa with pore canal plugs and a thick, fibrous zona radiata interna with a fibrous network on the inner surface. There was a two-layer adhesive coating over the zona radiata externa in all species except pink salmon in which only one layer was observed. There were structural differences among species in the adhesive layer, zona radiata externa and plugs in the pore-canal openings.

Animals↗
PubMed1986

The effect of dialysis of extended ram semen prior to freezing on post-thaw survival and fertility.

The effect of dialysis on extended ram semen prior to cryopreservation was studied. Techniques were developed to improve post-thaw recovery of dialyzed semen and a fertility trial was used to evaluate the viability of dialyzed and frozen semen. Dialysis prior to freezing was shown to increase post-thaw recovery of motile cells and percentage of cells passing through a Sephadex filter. Freezing semen in pellets on dry ice was superior to freezing in French straws. Pellets were thawed in an aluminum thaw block at 42 to 45 degrees C before insemination of progestagen-PMSG synchronized ewes. Double inseminations were made at 12-hr intervals. Natural service of synchronized ewes was also made at 12-hr intervals as a control. There was no significant difference (P greater than 0.05) in fertility between naturally serviced ewes (44.4%) and ewes inseminated with frozen semen (44.7%).

Animals↗
PubMed1986

The effects of nonpenetrating cryoprotectants added to TEST-yolk-glycerol extender on the post-thaw motility of ram spermatozoa.

The effects of adding five different concentrations of 17 polymeric compounds to TEST-yolk-glycerol extender on ram spermatozoa survival was studied. These were Aquacide (I, II, and III); dextran (0.8-1.6, 1.9, 15-20, 70, and 200-300 kDa); three types of Dri-Sweet; hydroxyethyl starch; methylcellulose, polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, and Supercol 912. All the compounds tested except the Dri-Sweet compounds and hydroxyethyl starch significantly (P less than 0.05) decreased percentages of motile cells in unfrozen samples. The use of dextran (0.8-1.6 kDa; hydrolyzed dextran separated by ethanol) and Aquacide II significantly (P less than 0.05) increased post-thaw motility of spermatozoa frozen in pellets. Dextran (15-20 kDa), dextran (0.8-1.6 kDa), Aquacide II, and hydroxyethyl starch significantly (P less than 0.05) increased the percentages of post-thaw motility of ram spermatozoa frozen in the presence of glycerol and egg yolk.

Animals↗
PubMed1982

Development of extender and techniques for frozen turkey semen. 1. Development.

An extender for turkey semen with a frozen-thawed recovery of greater than or equal to 50% motile spermatozoa and a vigorous swirl was developed. The effect of glucose, a comparison of 10 different sugars in the extender, the use of sodium acetate and potassium acetate, the ratio of dimethylsulfoxide to ethylene glycol, the percent total cryoprotectant, equilibration time, and osmotic pressure were all tested. Replacement of approximately half of the extender with an iso-osmolar glucose solution yielded higher percentages of motile spermatozoa with both fresh and frozen-thawed semen samples. Replacement of glucose with other carbohydrates did not enhance recovery of frozen-thawed semen. The proportion of sodium and potassium acetates to TESNaK2 in the extender had no effect on motility. Approximately equal proportions of ethylene glycol to dimethylsulfoxide, with a final concentration of 11.2% after dilution, produced at or near optimal recovery of spermatozoal motility after freezing. Twenty to 90 min equilibration times before freezing yielded significantly higher recovery of motile sperm postthaw than shorter periods. A wide range of extender osmotic pressures were compatible with recovery of spermatozoal motility postthaw. The final extender consisted of 4.70 g sodium acetate, 3.39 g potassium acetate 9.23 g TES, .353 g sodium hydroxide, .492 g potassium hydroxide, 32.00 g glucose, H2O q.s. 1000 ml, 370 mOsm/kg, pH 7.2. Ethylene glycol and dimethylsulfoxide were added (1:1 ratio) for a final concentration of 11.2% cryoprotectant after dilution. Semen was held undiluted for 6 min, extended 1:4 at 22 C, and equilibrated for 30 min at 0 C before pellet freezing.

Animals↗
PubMed1982

Development of extender and techniques for frozen turkey semen. 2. Fertility trials.

The effects of cryoprotectant concentrations, redilution, centrifugation, and dialysis techniques on fertility of fresh and frozen-thawed turkey semen were tested. Fresh extended semen with final concentrations of 4.8, 5.6, 9.6, and 11.2% cryoprotectant (dimethylsulfoxide and ethylene glycol, 1:1 ratio) showed a significant (P less than .05) decrease in fertility when compared to semen without cryoprotectant. Fertility of fresh semen extended with 4.8% cryoprotectant when centrifuged or rediluted and centrifuged, was unaffected when compared to cryoprotectant treated semen. Fertility of frozen-thawed semen after redilution and centrifugation was low, but samples rediluted one part semen for two parts extender yielded significantly (P less than .05) higher fertility than semen rediluted 1:1. Fresh semen extended with 11.2% cryoprotectant showed a highly significant (P less than .01) decrease in fertility despite dialysis, while semen with 9.6% cryoprotectant showed no difference when compared to dialyzed semen without cryoprotectant. Fertility of frozen-thawed semen dialyzed against blood plasma (approximately pH 7.9) and blood plasma adjusted with TES2 to pH 7.4 or pH 7.2 was not significantly different. Fertility of frozen-thawed semen dialyzed for 30 min was significantly higher (P less than .01) than semen dialyzed for 15 min or 0 min. Frozen-thawed semen dialyzed with a semen to dialysate ratio of 1:15 and 1:24 supported significantly higher (P less than .01) fertility than at 1:50 ratio. The AGPT3 dialysate yielded significantly higher (P less than .01) fertility than blood plasma adjusted to pH 7.2 with TES.

Animals↗