Biomedical subjects

David J Weiss

Publications and source records attributed to David J Weiss.

9 recordsLinked to original sources

PubMed2006

Dehydrogenase based reagentless biosensor for monitoring phenylketonuria.

Phenylketonuria (PKU) is a disease characterized by an inability to metabolize the amino acid l-phenylalanine. The resulting buildup leads to brain damage and ultimately mental retardation in children if their phenylalanine intake is not carefully controlled. The National Institutes of Health recently suggested that people with PKU monitor their phenylalanine levels throughout their life and be put on a low phenylalanine diet. As an alternative approach to analysis using blood, this paper describes the first reagentless dehydrogenase based sensor for the determination of phenylalanine in human urine. The clinical range of phenylalanine in human urine is 20-60mM for people with PKU. Although most clinical analysis is performed using blood, urine was chosen due to its high concentrations of phenylalanine in phenylketonurics, as well as its simple, safe, and painless collection. The sensor is comprised of a carbon paste electrode with nicotinamide adenine dinucleotide (NAD(+)), phenylalanine dehydrogenase (PDH), uricase, and an electron mediator, 3,4-dihydroxybenzaldehyde (3,4-DHB), all mixed into the paste. The electron mediator reacts with the electrode surface to produce two redox species, which catalytically oxidize NADH. The behavior of the electron mediator mixed into a carbon paste electrode has not been previously investigated. Cyclic voltammetry was used to characterize the sensor's response to NADH, and with the addition of PDH and NAD(+) to the paste, its response to phenylalanine in human urine. The limit of detection for phenylalanine is 0.5mM (S/N=3).

Amino Acid Oxidoreductases↗

PubMed2006

Analysis of green tea extract dietary supplements by micellar electrokinetic chromatography.

Dietary supplements are growing in popularity as a source of catechins such as epigallocatechin gallate (EGCG). The first determination of five catechins in green tea extract dietary supplements using an extraction followed by micellar electrokinetic chromatography (MEKC) with UV detection is presented here. The optimum run buffer is 5 mM borate-60 mM phosphate with 50 mM SDS at pH 7.00 with detection at 210 nm. The limit of detection is 2-3 microg/mL (S/N=3) and the limit of quantitation is 6-8 microg/mL (S/N = 10). Results indicate that the amount of catechins varies greatly among manufacturers, between capsules of the same manufacturers, and between batches.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2005

Motivation to quit as a mediator of tobacco cessation among at-risk youth.

The purpose of this study is twofold: 1) to evaluate the effects of a smoking cessation clinic (Project EX) on changing motivation to quit smoking, and 2) to assess differences in quit rates based on these changes in motivation. Student smokers in 18 continuation high schools in the Los Angeles county area were invited to participate in a tobacco cessation clinic designed to enhance motivation to quit tobacco use. The 18 schools were randomly assigned to one of three conditions. Compared to students in the control group, students who participated in the program conditions were more likely to express higher motivation to quit tobacco use. Higher motivation was also significantly related to higher quit rates. Motivation to quit as defined by constituents of the energy/direction model of motivation appears to be a plausible mediator of cessation program effects.

Adolescent↗

PubMed2005

Analysis of natural flavonoids by microchip-micellar electrokinetic chromatography with pulsed amperometric detection.

Catechins (catechin and other derivatives) are naturally occurring flavonoids present in a number of plants and foods. They are also part of numerous nutraceutical formulations because they are believed to have antioxidant, cancer chemo-preventative, anti-inflammatory and antimicrobial properties. The determination of catechins has traditionally been performed by HPLC. However, this methodology is both time and sample intensive and generates large amounts of organic solvent waste. In the current report, an application of MEKC using a PDMS microchip is presented for the analysis of catechins. The system uses pulsed amperometric detection for direct analysis of important naturally occurring catechins. The effect of pH, surfactant concentration, detection potential and signal stability were analyzed. Linear relationships were found between the concentration and peak current, with good stability and limits of detection of 8 [micro sign]M for catechin, epigallocatechin gallate and epicatechin, and 14 [micro sign]M for epicatechin gallate. Optimum conditions were applied to the detection of selected catechins in a commercially available green tea extract nutraceutical and the results were compared to HPLC analysis. The analysis using microchip micellar electrokinetic chromatography and pulsed amperometric detection was completed in 4.5 min, 10 times faster than the HPLC analysis.

Catechin↗

PubMed2005

A mean for all seasons.

The averaging of scores differs from the averaging of numbers in that behavioral issues are built into scores. The behavioral issues are the weight attached to a score and the metric on which the scores have been gathered. A single equation is proposed, derived from Aczél's (1966) model of the quasilinear mean, that encompasses the standard measures of central tendency. The equation allows for differential weighting of scores and also addresses the metric issue by incorporating response transformation.

Body Weight↗

PubMed2004

Haptic rendering of tissue cutting with scissors.

Current surgical simulations that involve cutting with scissors lack display of forces "between the fingers" of the operator. The objective of this work is to develop a fast, realistic haptic rendering technique for scissor cutting that can be easily integrated into soft tissue models commonly used in surgical simulators. A virtual environment was created for combined graphic and haptic display of cutting. Two 2-dimensional deformable mass-spring-damper models were developed: The first is a large mesh that is used to calculate translational forces. The second is a smaller, one-element-thick mesh that is used to calculate cutting (angular) forces. This technique was implemented on the haptic scissors, a haptic interface that allows motion and force feedback in translation and cutting.

Computer Graphics↗

PubMed2003

Determination of catechins in matcha green tea by micellar electrokinetic chromatography.

Catechins in green tea are known to have many beneficial health properties. Recently, it has been suggested that matcha has greater potential health benefits than other green teas. Matcha is a special powdered green tea used in the Japanese tea ceremony. However, there has been no investigation to quantitate the catechin intake from matcha compared to common green teas. We have developed a rapid method of analysis of five catechins and caffeine in matcha using micellar electrokinetic chromatography. Results are presented for water and methanol extractions of matcha compared with water extraction of a popular green tea. Using a mg catechin/g of dry leaf comparison, results indicate that the concentration of epigallocatechin gallate (EGCG) available from drinking matcha is 137 times greater than the amount of EGCG available from China Green Tips green tea, and at least three times higher than the largest literature value for other green teas.

Catechin↗

PubMed2003

Vastus lateralis strain associated with patellofemoral pain syndrome: a report of 2 cases.

Muscle strains of the quadriceps group are common, and occur mostly in the rectus femoris. Strains occur most often when muscles are suddenly activated while on stretch, during either eccentric or concentric contraction. We report 2 cases of vastus lateralis strain that occurred in association with clinical histories of patellofemoral pain syndrome. Symptoms described included anterior knee pain associated with prolonged sitting with the knee flexed, and anterior knee pain associated with running, stair climbing, and jumping. These symptoms preceded the acute strain by at least 1 year. These cases emphasize a clinician's need to understand knee biomechanics, and the need to consider the entire kinetic chain when managing pain and injury in an extremity.

Adult↗

PubMed2003

Empirical assessment of expertise.

The assessment of expertise is vital both in practical situations that call for expert judgment and in theoretical research on the psychology of experts. It can be difficult, however, to determine whether a judge is in fact performing expertly. Our goal was to develop an empirical measure of expert judgment. We argue that two necessary characteristics of expertise are discrimination of the various stimuli in the domain and consistent treatment of similar stimuli. We combine measures of these characteristics to form a ratio we call the Cochran-Weiss-Shanteau (CWS) index of expertise. The proposed index was demonstrated using two studies that distinguished experts from nonexperts based on their judgmental performance. The index provides new insights into expertise and offers a partial definition of expertise that may be useful in a variety of theoretical and applied settings. Potential applications of this research include selection, training, and evaluation of experts and of expert-machine systems.

Behavior↗