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Biomedical subjects

L C Clark

Publications and source records attributed to L C Clark.

At least 73 records · Page 4Linked to original sources
PubMed1984

Rapid electroenzymatic measurement of lactate in microsamples of spinal fluid.

A lactate sensor, which makes possible rapid direct measurement of L-lactate in small samples of spinal fluid, has been developed. This enzyme electrode gives a linear current output as a function of hydrogen peroxide generated by a lactate oxygen oxidoreductase sandwiched between two membranes. The membranes serve to support the oxidase, prevent the diffusion of soluble electroactive species such as urate, ascorbate, and phenolic drugs such as acetaminophen, and to form a diffusion-limited path for the lactate. A 10 or 25 microL sample of spinal fluid is injected into a 350 microL thermostated chamber containing a suitable buffer and the electrode's sensing surface. The method has been tested by analysis of spinal fluid, with amounts of lactate up to 15 mmol/L, by comparison with a photoenzymatic method. A correlation coefficient of 0.999 was found. With a new cellulose ester membrane, acetaminophen levels up to 10 mmol/L did not interfere. A YSI glucose analyzer can be converted to a lactate analyzer by changing the O-ring mounted enzyme transducer membrane.

Electrodes↗
PubMed1984

Rapid micromeasurement of lactate in whole blood.

A new lactate sensor makes it possible to measure the lactate content of whole blood directly in less than 1 min, using only a 10-microL blood sample. The procedure works equally well with plasma, serum, spinal fluid, other body fluids, or tissue homogenates. The instrument is calibrated with lactate standards between 0 and 15 mMol/L. The sensor, a polarographic enzyme electrode, gives a current which is a linear function of the lactate concentration. There is no interference from glucose, pyruvate, alcohol, ascorbate, anticoagulants, lidocaine, acetaminophen, or other drugs and metabolites commonly encountered in critically ill patients. The lactate sensor is composed of a peroxide sensor and an enzyme transducer membrane. The lactate is stoichiometrically converted to pyruvate and hydrogen peroxide by lactate oxygen oxidoreductase derived from Pediococcus species. The oxygen required for the enzymatic oxidation is supplied via an air-permeable silicone elastomeric membrane used for stirring. Comparison of our new electroenzymatic method with the Boehringer-Mannheim photoenzymatic method gives correlations of 0.997 for both whole blood and plasma.

Alcohol Oxidoreductases↗
PubMed1984

Plasma selenium and skin neoplasms: a case-control study.

Although experimental studies in animals show that selenium may prevent cancer, case-control studies of internal human cancers have been difficult to interpret because neoplastic tissue sequesters selenium. We therefore conducted a case-control study to examine the association between plasma selenium level and skin cancer, a neoplasm with minimal tumor mass at the time of diagnosis. The mean selenium level among patients with either basal cell epithelioma (N = 142), squamous cell carcinoma (N = 48), or both (N = 50), was 0.141 micrograms/g. This was significantly lower than the mean plasma selenium level of the 103 control subjects, which was 0.155 micrograms/g. The noncancer control groups were drawn from current clinic patients and past clinic patients. The logistic estimate of the odds ratio for the lowest versus the highest decile of selenium for all cases combined versus the group of current patient controls was 4.39; for all cases combined versus the past patient controls, the logistic estimate of the odds ratio was 5.81.

Adult↗
PubMed1981

Fluorocarbons reduce myocardial ischemic damage after coronary occlusion.

Open-chest, anesthetized dogs with occlusions of the left anterior descending coronary artery breathed 100 percent oxygen while they were bled to a hematocrit of 25 percent and infused with an approximately equal volume (40 milliliters per kilogram) of fluorocarbon preparation or Ringer solution. Dogs breathing room air and receiving no treatment served as controls. After undergoing 6 hours of coronary occlusion, animals bled and treated with fluorocarbons developed smaller infarctions than those receiving Ringer solution or no treatment.

Animals↗
PubMed1981

One-minute electrochemical enzymic assay for cholesterol in biological materials.

In this rapid and specific micro-scale electrochemical enzymic assay for cholesterol and cholesterol esters, 10 microL of standard or sample is injected directly into a heated (50 degrees C) thermostated, oxystated cuvet containing pH 7.25 buffer, cholesterol oxidase (EC 1.1.3.6), and cholesterol esterase (EC 3.1.1.13). The cholesterol esters are hydrolyzed by the esterase, and the cholesterol is simultaneously oxidized by the oxidase. The hydrogen peroxide produced from oxidation of the unesterified cholesterol is measured by a polarographic anode covered with an acetate/polycarbonate membrane. The membrane allows hydrogen peroxide to diffuse to the platinum anode, where it is oxidized, but prevents the diffusion of ascorbic acid, uric acid, and bilirubin to the electroactive surface. Turbidity does not interfere. The correlation (r) between results by our method and the Abell-Kendall method for 105 samples of serum was 0.9994 and for 105 samples of plasma was 0.9997. Our method is convenient for the analysis of high-density lipoprotein cholesterol in plasma and serum supernates and in many kinds of tissue homogenates. Its limitations are also described.

Cholesterol↗