Search PubMed⌕ Search

Biomedical subjects

D D Koch

Publications and source records attributed to D D Koch.

At least 145 records · Page 8Linked to original sources
PubMed1983

Evaluation of a direct potentiometric method for sodium and potassium used in the Du Pont aca.

We evaluated an accessory that enables the Du Pont aca discrete analyzer to measure Na+ and K+ by direct potentiometry (aca/ISE). Na+ and K+ gave linear responses in both the blood and urine modes, with no carryover. No interfering species were identified in the blood mode. Intra-assay and interassay precision for Na+ and K+ were more than adequate and analytical recoveries comparable to those with flame photometry were found for plasma. The Na+ and K+ values for plasma were comparable with those obtained by use of another direct potentiometric analyzer (the Orion SS-30), but slightly higher than flame-photometric values. Samples from patients with hyperlipemia and multiple myeloma gave clinically relevant values with the aca/ISE, but the flame photometric values were artefactually low. Whole blood could not be accurately analyzed. The aca/ISE is a precise, easy-to-use instrument, which gives values for plasma similar to those obtained with direct potentiometric analyzers. For analysis of urine, certain precautions are necessary.

Autoanalysis↗
PubMed1982

Sodium measurements in multiple myeloma: two techniques compared.

Sodium was determined by flame photometry and by direct potentiometry in 56 serum or plasma samples from 24 patients with multiple myeloma or macroglobulinemia. We observed differences between the two techniques as large as 17 mmol/L (12%). The flame-photometric values decreased relative to the direct-potentiometric values as protein increased or water content decreased. Moreover, the two sodium measurements could not be interconverted simply on the basis of correcting for protein or water content. There was significantly lower residual variance (p less than 0.005) when the direct-potentiometric sodium values were compared with the osmolality (corrected for the influence of glucose and urea nitrogen) than when the flame-photometric values for sodium were so compared. We conclude that direct potentiometric measurements of sodium in patients with multiple myeloma gives clinically relevant results but flame photometry does not. Clearly, the method by which sodium is measured in patients with multiple myeloma must be considered if results are to be interpreted correctly.

False Negative Reactions↗
PubMed1982

Biochemical features of urinothorax.

In three patients with obstructive uropathy and retroperitoneal urine collections, rapidly accumulating pleural effusions developed. The diagnosis of urinothorax was confirmed when chemical analysis of pleural fluid disclosed higher creatinine concentrations than found in simultaneously obtained serum samples. Similar determinations made in 71 specimens from control patients with pleural effusions showed that pleural creatinine concentration did not exceed the serum level in other conditions. We conclude that elevated pleural fluid creatinine level is specific for the diagnosis of urinothorax. Low pleural fluid glucose concentration may also be seen in these patients.

Aged↗
PubMed1982

Relationship between direct-potentiometric and flame-photometric measurement of sodium in blood.

The relationship between direct-potentiometric and flame-photometric measurements of sodium has been studied in human sera and other, simpler systems. When water content was varied by using an inert substance (silica), de-ionized sera, or de-ionized individual proteins, the percentage that the flame photometric values were of the direct potentiometric Na+ values was identical to the measured water content. However, in 35 patients the percentage of Na+ values was 99.1% and the water content was 92.0%, a discrepancy of 7.1%. De-ionization of sera removed this discrepancy, apparently because of the lower pH of the de-ionized sera. The percentage of flame-photometric to direct-potentiometric Na+ values varied as a function of pH in pooled sera; in lyophilized and reconstituted sera; and in de-ionized, lyophilized, and reconstituted sera. Four explanations for the discrepancy between the percentage of Na+ values and the water content are discussed: a calibration problem, a measurement artifact, Na+ binding, and water binding. At this time there are no definitive data concerning which explanation is correct. We expect that our finding of a pH dependency for the percentage of measured Na+ values can be used to develop model systems to elucidate the mechanism producing the discrepancy between the percentage of Na+ values and the water content.

Bicarbonates↗
PubMed1981

Intrathoracic extension of retroperitoneal urine collections.

Five patients with retroperitoneal urine collections (urinomas) had clinical and radiographic evidence of intrathoracic disease. All five patients rapidly accumulated pleural fluid, documented chemically in three patients to be urine. Two patients developed acute mediastinal widening which rapidly cleared after surgical drainage of the retroperitoneal urinoma. Although rare, thoracic collections of urine should be considered when pleural effusions or mediastinal widening occur in patients with urinary tract obstruction or retroperitoneal urinomas.

Aged↗
PubMed1979

Determination of tryptophan and several of its metabolites in physiological samples by reversed-phase liquid chromatography with electrochemical detection.

A new method for the concurrent assay of three tryptophan metabolites at the picomole level is described. The method has been developed for blood, urine, cerebrospinal fluid, and tissue samples such as whole brain, brain parts, and endocrine glands. Tryptophan itself, serotonin, and 5-hydroxyindoleacetic acid are isolated initially on extraction columns, eluted with a suitable solvent, and injected onto a liquid chromatograph with an amperometric detector. This general approach may be applicable to a variety of other tryptophan metabolites and should be useful in both research and clinical investigations.

Adult↗
PubMedDate not supplied

Laboratory evaluation of new reusable blood glucose sensor.

An enzyme-electrode sensor designed specifically for pocket-portable self-monitoring of blood glucose is described. The sensing device in this instrument is unique because it is reusable for at least 30 days, at which time it is easily replaced by placing a new enzyme-membrane cartridge over the electrode. As little as 7 microliters of undiluted whole blood, plasma, or serum is applied directly to the sensor, and glucose is automatically determined in 30 s. No manual timing or wiping step is required after sample application. On eight production instruments, plasma glucose concentration was determined (n = 20) at 57, 125, 246, and 347 mg/dl. The average coefficient of variation for the 80 determinations for each instrument ranged from 2 to 5%, averaging 3.7%. The instrument is inherently linear, independent of hematocrit, and without oxygen limitation when dissolved oxygen concentration is greater than 35 mmHg. No interferences were found from plasma constituents, heparin, or acetaminophen.

Biosensing Techniques↗
PubMedDate not supplied

Histologic changes and wound healing response following 10-pulse noncontact holmium:YAG laser thermal keratoplasty.

BACKGROUND: Noncontact holmium:YAG laser thermal keratoplasty (Ho:YAG LTK) is a promising new technology for correction of hyperopia and astigmatism. We studied the acute histologic changes and wound healing response following Ho:YAG LTK performed with treatment parameters encompassing those used in clinical studies. METHODS: We performed 10-pulse noncontact Ho:YAG LTK on three human corneas 1 day before their removal at penetrating keratoplasty and on six New Zealand white rabbit corneas followed for up to 3 months. Tissues were studied with light and transmission electron microscopy and immunohistochemistry. RESULTS: The amount of acute tissue injury increased according to the pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death, loss of fine filamentous structure in Bowman's layer, disruption of stromal lamellae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbits included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation. CONCLUSIONS: Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response.

Animals↗
PubMedDate not supplied

Photoastigmatic refractive keratectomy in myopes. Nidek US Investigators Group.

PURPOSE: Photoastigmatic refractive keratectomy (PARK) was studied in a multi-center clinical trial. The Nidek EC-5000 excimer laser was evaluated for its effect on refraction, visual acuity, and safety measures as part of a U.S. Food and Drug Administration (FDA) regulated study. METHODS: Eight U.S. centers enrolled adults with eyes having refractive astigmatism up to 4.00 D and a myopic spherical equivalent refraction up to -8.00 D. Results are reported for 749 eyes of 486 patients with at least 6 months follow-up. The rectangular beam scanning Nidek EC-5000 used a 5.5-mm-diameter treatment zone, a 7.0-mm-diameter peripheral blend zone, and a 40 Hz pulse rate for surface treatment of myopic astigmatism. Nomogram corrections to machine settings were required to achieve the desired results. RESULTS: Preoperative average spherical equivalent refraction of -4.90+/-1.74 D was reduced to -0.02+/-0.79 D at 6 months. Refractive stability was established at 3 months. Over 62% of eyes were within +/-0.50 D of desired correction at 6 months, with over 86% within +/-1.00 D. Uncorrected visual acuity improved by an average of 10 Snellen lines; over 64% of eyes saw 20/20 or better uncorrected and over 93% saw 20/40 or better uncorrected at 6 and 12 months. PARK treatment effectively reduced astigmatism with little average axis error or magnitude error. Corneal haze and safety concerns were minimal. CONCLUSIONS: Photoastigmatic refractive keratectomy using the Nidek EC-5000 excimer laser provided significant reduction of myopia and astigmatism, with minimal complications.

Adult↗
PubMedDate not supplied

Analytical performance characteristics of the T4 method in the Abbott AxSYM immunoassay analyzer.

OBJECTIVE: To evaluate the tetraiodothyronine (T4) method in the Abbott AxSYM immunoassay analyzer. DESIGN: The single-value criteria proposed by Westgard et al. were employed. Assays of control materials established random error (RE) analytical sensitivity, and linearity. Constant error (CE) was established by studying the effects of interferents on T4 quantification. The AxSYM random access immunoassay analyzer was compared with TDx batch analyzer to determine systematic error (SE). Critical concentrations of T4 are 3.0 micrograms/dL and 13.0 micrograms/dL, as these concentrations represent medical decision points. Allowable error at these critical concentrations are 1.0 and 2.6, respectively. SETTING: Peninsula Regional Medical Center Clinical Laboratories. RESULTS: Based on Health Care Financing Administration [HCFA] allowable error goals, RE, SE, and CE were acceptable for concentrations of T4 ranging from 3.0 micrograms/dL to 13 micrograms/dL. PE was virtually absent. Total error (TE) = RE + SE was acceptable at 13 micrograms/dL but exceeded allowable error at the lower critical value of 3.0 micrograms/dL. Abbott AxSYM was sensitive to T4 at a concentration of 0.34 microgram/dL. Linearity was excellent and consistent with the manufacturer's claim over a range 1.0 microgram/dL to 24 micrograms/dL. Of the interferents studied only hemoglobin caused a > 15% change in the measurement of T4. CONCLUSION: The AxSYM immunoasssay analyzer performed to manufacturer's specifications and met HCFA allowable error limits for quantifying T4.

Bias↗
PubMedDate not supplied

The Corneal EyeSys System: accuracy analysis and reproducibility of first-generation prototype.

The EyeSyS Corneal Topography System manufactured by EyeSys Laboratories, Inc., Houston, Tex utilizes a unique data-acquisition design to perform rapid, cost-effective quantitative photokeratoscopy. We evaluated a first-generation prototype system. Repeated testing with this prototype demonstrated an accuracy and reproducibility to within 0.25 D on spherical surfaces. Similar results were obtained in testing aspherical surfaces without refocusing. Data from preliminary clinical studies are displayed for the following corneal conditions: normal, keratoconus, post-keratoplasty, and post-keratoplasty with wound ectasia. Advantages of the EyeSys System include rapid data analysis and display, ease of operation, and compact table-top size.

Adult↗
PubMedDate not supplied

Irregular astigmatism induced by annular tinted contact lenses.

Three patients developed irregular corneal astigmatism while wearing annular tinted soft contact lenses on a daily basis for 1.5 to 3 years. There was severe keratometer mire distortion, and photokeratoscopy revealed central and midperipheral corneal topographical irregularities in four of six eyes. In a masked protocol, scanning electron microscopy of four contact lenses revealed physical deformations in three lenses worn on affected eyes. We propose that latent stress vectors were created when the affected contact lenses were tinted. With patient usage, the stress vectors matured into physical deformations that induced irregular astigmatism. The astigmatism resolved upon discontinuing wear of these lenses, and the patients were able to wear other lenses with no recurrence of symptoms.

Adult↗
PubMedDate not supplied

High altitude corneal endothelial decompensation.

A 77-year-old patient with low endothelial cell counts sustained acute unilateral endothelial decompensation when he traveled to an elevation of 12,500 feet. The corneal edema gradually increased after his return to sea level, and penetrating keratoplasty was required to restore vision. To our knowledge, this is the first reported case of hypoxia-induced corneal endothelial decompensation.

Aged↗