John I. Peterson

Retinal oxygenation and laser treatment in patients with diabetic retinopathy.

The oxygen tension in the preretinal vitreous cavity was measured in human patients undergoing vitreous operations for proliferative diabetic retinopathy. The oxygen tension was significantly higher (P = .004) over areas of retina that had been treated with panretinal photocoagulation than it was over untreated areas in the same retina. This confirmed previous results in animals that showed that panretinal photocoagulation increases the inner retinal oxygen tension. We concluded that panretinal photocoagulation improves the oxygen supply to the inner retina and thereby minimizes the influence of retinal ischemia in diabetic retinopathy.

Evaluation of the hexokinase-glucose-6-phosphate dehydrogenase method of determination of glucose in urine.

Abstract The two-step enzymic method for determination of glucose, using hexokinase for phosphorylation of the glucose and glucose-6-phosphate dehydrogenase for the subsequent reduction of triphosphopyridine nucleotide to its reduced form measurable at 340 nm, was evaluated for its suitability for urine analysis. The glucose oxidase method, previously considered the best available, is subject to serious interference which cannot be removed without destroying the accuracy of the method. The hexokinase/G6PD method is highly specific and interference-free. The only possible urinary interference that could be found is a diminution of the glucose indication in the presence of extremely abnormal fructose concentrations. The method was tested for recovery on 100 clinical urine samples. A normal range of 0 to 20 mg 100 ml glucose was indicated by these samples. The method may also be used for blood analysis as normal concentrations of preservative did not interfere. The general analytical and kinetic characteristics of the method were examined, showing that the method may be used accurately at ambient temperatures, with a straight line standard curve, at an incubation time of 10 min, for sample concentrations up to 100 mg 100 ml . The method may be used for screening purposes without determining the background ultraviolet absorbance of the sample.

New technique of surface flow visualization based on oxygen quenching of fluorescence

A surface pattern flow visualization technique is demonstrated based on the principle of oxygen quenching of dye fluorescence. The technique uses visible light excitation and streams of oxygen or nitrogen, which are inexpensive and nontoxic. A sensitive material can be spray coated on shapes of interest to study flow at surfaces.

A system for convenient combustion preparation of tritiated biological samples for scintillation analysis

Abstract A combustion system is described which makes possible the routine preparation of large numbers of biological samples for scintillation counting. The system accepts a variety of sample materials, and a method is provided for evaporating tissue homogenate in gelatin or plastic capsules. An operator drops a capsule in the furnace and collects the combustion products in scintillation solvent, ready for counting, at a rate of 1 sample every 3 min. The system accepts samples of at least 500 mg, limited by solvent capacity for water. A favorable comparison with the oxygen flask method is shown and there is minimum carryover of activity in successive samples. The method has a collection recovery of 96%, is calibrated by internal standards, and shows a coefficient of variation of 2.9%.

A carbon dioxide collection accessory for the rapid combustion apparatus for preparation of biological samples for liquid scintillation analysis

Abstract A carbon dioxide collection accessory is described for the previously reported combustion system for preparation of biological samples for liquid scintillation counting. A sample can be burned and collected every 3 min. Sample size is limited by the capacity of the solvent to absorb carbon dioxide without precipitation. The system can be used for collecting water as well as carbon dioxide, for double isotope counting. The method has a collection recovery of 97%, is calibrated by internal standards, and shows a coefficient of variation of 1.1%.

A fiber-optic broad-range pH sensor system for gastric measurements

Abstract The construction and performance of a fiber-optic broad-range pH sensor system are described. The general construction of the sensor is similar to the original fiber-optic pH sensor, but two dyes with three p K values have been immobilized to provide resonse over the pH range of 0.5–7 with a precision better than 0.1 pH unit. The range extends to pH9 with less precision. The primary objective of the design is for gastric measurements. The system is based on absorbance dyes bound to polyacrylamide gel containing light-scattering particles. The sensor is constructed on a single 0.25-mm diameter plastic optical fiber. The optical system consists of a tungsten lamp, fiber-optic splitter and CCD/grating detector connected to a computer for spectral analysis, using two wavelength regions. The computer displays the pH graphically over 24 h. The system shows stability within 0.2 pH unit over 24 h, and has been tested with gastric samples in a dog.

A gel slicer for the transverse sectioning of cyclindrical polyacrylamide gels

Abstract A transverse sectioning device for cylindrical polyacrylamide gels has been constructed which provides 1 mm-thick gel slices with a precision from 13 to 34%, depending on the gel type and operator skill: 1. a—without freezing or other pretreatment of the gel 2. b—on materials varying widely in gel concentration, in the degree of crosslinking and in the nature of the crosslinking agent 3. c—with sufficient speed of slicing to allow analysis of 20 or more samples/day per operator.

A Miniature Fiberoptic pH Sensor Potentially Suitable for Glucose Measurements

A fiberoptic sensor that we have developed for measuring physiologic pH is a potentially useful model for similar probes for other important applications such as monitoring glucose in the body. A fiberoptic probe has important advantages over an electrode in safety, reliability, applicability, and cost. The pH probe is described, with suggested approaches for making a device for glucose measurement.

An instrument for performing laser capture microdissection of single cells

We have developed a new form of laser capture microdissection (LCM) optimized for isolating and concentrating single cells from a tissue slide for subsequent molecular analysis. In LCM an infrared laser diode is used together with a microscope to locally melt a thin film of ethylene vinyl acetate (EVA) placed in contact or close proximity to microscopically targeted cells. Since the desired cells adhere to the film where it has been melted, they are extracted from their adjacent tissue in the specimen when the film is separated from the slide. In our system the EVA is bonded to a cylindrical substrate resulting in a very small area of contact between the EVA and the slide which minimizes contamination to levels consistent with analyzing a few cells of a selected cell type. By collecting cells at different portions about the cylinder periphery, the novel geometry also allows the concentration of cells from different slides onto a single substrate, enabling very sensitive molecular analysis to be performed ...

Fiber optic pH sensor for gastric measurements: preliminary results

This paper describes preliminary results on the development of a fiber optic pH sensor for gastric measurements. As the pH values in the gastric system vary from approximately 1 to 7, a combination of appropriate dyes to cover this broad range should be used. pH colorimetric indicators bound in polyacrylamide microspheres and light scattering particles are packed in a cellulosic dialysis tubing at the end of a pair of plastic optical fibers. The experimental setup uses a CCD spectrometer as a detector and a 386 compatible personal computer. All parameters can be set by software. Results with both one-dye and two-dye pH sensors are presented.