Quality specifications for evaluation and comparison of performance among external quality assessment schemes in occupational and environmental laboratory medicine

Quality specifications (QS) are proposed for lead in blood and for aluminium, copper, selenium and zinc in serum as part of the aim to set standards of performance for laboratories so that results can be demonstrated to be fit for the purpose to which they are applied. The QS were established taking account of the analytical state-of-the-art, physiological variations in the concentrations of the analyte and the clinical purpose for which the assay is to be used. A procedure was devised that uses these QS to give equivalence of assessment among external quality assessment schemes (EQAS), thus avoiding conflicting information which has been demonstrated in the past. Advantages of this procedure are: to provide direct comparison of performance of laboratories taking part in different schemes, to provide equivalence of assessment of laboratory performance necessary to establish mutual recognition agreements, and to demonstrate the fitness for purpose of results from participants.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Microcalorimetric study of the growth of Enterococcus faecalis, Klebsiella pneumoniae and their mixtures in an enriched culture medium

In the last few years there has been a growing interest in microcalorimetric investigations of microbial processes. Microcalorimetry is a technique based on heat output of bacterial metabolism which can be applied to detect bacterial growth in a few hours. However, there are few studies that attempt to investigate the interactions between two or more bacteria. In this study, we researched the interaction relationship of Enterococcus faecalis and Klebsiella pneumoniae, which are important pathogens responsible for infections in humans. The measures were carried out using a Calvet microcalorimeter, that contains two stainless steel cells of approximately 10 cm³ (reference and experimental). Experiments were carried out at concentration of 10³ CFU mL^?1 and a constant temperature of 309.65 K. The differences in shape of the heat flow-time curves of E. faecalis and K. pneumoniae and their mixtures were compared. Curves of E. faecalis and K. pneumoniae and their mixtures were analyzed mathematically allowing to calculate thermokinetic parameters such as growth constant (k), generation time (G), detection time (t _d) and the amount of heat released (Q). The results revealed that when E. faecalis and K. pneumoniae were put together in the same proportion, the growth character of E. faecalis was not present, due to the inhibitory effects of K. pneumoniae on E. faecalis. Microcalorimetric investigations of microbial interactions is possible and promising.     

The traceability chain in medical laboratories: a long and winding road, the example of HbA1c

In medical laboratories, a metrological basis for quantitation is missing for many tests. This is recognised by the profession and over the last decade the concept of metrological traceability is advocated. However, daily practice is refractable: for many analytes reference measurement procedures are missing and once in place, clinicians obstruct the new units. This wearisome process is described in general terms and illustrated by the specific case of HbA_1c. A working group of the scientific division of the IFCC developed a reference system for this key parameter in diabetes management. This system is worldwide accepted as the analytical anchor. However, clinicians objected the new units. A debate of years followed. This urged the international diabetes organisations IDF, EASD and ADA to find a solution to avoid confusion. They came up with a consensus statement, but this compromise—report of HbA_1c in three units—was unpractical and not accepted. Finally, decisions were made at a national level: the European Union and Japan will report in the new units, the US in their old national units and an additional unit, the estimated average glucose.     

High-Throughput Griess Assay of Nitrite and Nitrate in Plasma and Red Blood Cells for Human Physiology Studies under Extreme Conditions

The metabolism of nitric oxide plays an increasingly interesting role in the physiological response of the human body to extreme environmental conditions, such as underwater, in an extremely cold climate, and at low oxygen concentrations. Field studies need the development of analytical methods to measure nitrite and nitrate in plasma and red blood cells with high requirements of accuracy, precision, and sensitivity. An optimized spectrophotometric Griess method for nitrite–nitrate affords sensitivity in the low millimolar range and precision within ±2 μM for both nitrite and nitrate, requiring 100 μL of scarcely available plasma sample or less than 50 μL of red blood cells. A scheduled time-efficient procedure affords measurement of as many as 80 blood samples, with combined nitrite and nitrate measurement in plasma and red blood cells. Performance and usefulness were tested in pilot studies that use blood fractions deriving from subjects who dwelt in an Antarctica scientific station and on breath-holding and scuba divers who performed training at sea and in a land-based deep pool facility. The method demonstrated adequate to measure low basal concentrations of nitrite and high production of nitrate as a consequence of water column pressure-triggered vasodilatation in deep-water divers.     

A two-stage model for a day-ahead paratransit planning problem

We consider a dynamic planning problem for paratransit transportation. The focus is on a decision to take one day ahead: which requests to serve with own vehicles, and which requests to subcontract to taxis? We call this problem the day-ahead paratransit planning problem. The developed model is a non-standard two-stage integer recourse model. Both stages consist of two consecutive optimization problems: the clustering of requests into routes, and the assignment of these routes to vehicles. To solve this model, a genetic algorithm approach is used. Computational results are presented for randomly generated data sets.     

Measurement of the properties of a CO2 laser induced air-plasma by double floating probe and spectroscopic techniques

The laser-induced breakdown spark has recently been advanced as a method for real-time, in-situ spectrochemical analysis of gases. Many of these analyses take place in ambient air. To better characterize this source, we have measured the temporal variation of temperature and electron density in an air plasma induced by a CO₂ laser operating at 0.5 and 0.8 J/pulse. The electron temperature was measured by the double floating-probe technique (DFP). An excitation temperature for oxygen atoms was determined spectroscopically by Boltzmann plots. Electron density in the plasma was measured from the Stark broadening of the 715.6-nm line of 01. At 0.5 J/pulse, the DFP temperature ranged from 175000 K at 5 μs to less than 10000 K at 25 μs, while the 01 excitation temperature ranged from 19000 K at 1 μs to above 11 000 K at 25 μs. The excitation temperature and electron density agree with values calculated by others from local thermodynamic equilibrium models of an air plasma. While the electron temperature from the DFP method is much higher than the excitation temperature at 5 μs, at times greater than 25 μs the two have converged, implying thermodynamic equilibration between the species.     

The Voice Handicap of Student-Teachers and Risk Factors Perceived to Have a Negative Influence on the Voice

A cross-sectional questionnaire survey was performed. The objectives of the study were to assess the psychosocial impact of current voice complaints as perceived by student-teachers with voice complaints in comparison with student-teachers without voice complaints, and to observe the pattern of risk factors in relation to their voice handicap. Subjects in the general population without a voice-demanding profession were selected as a reference group for limited comparison with the total group of student-teachers (future professional voice users). The respondents to the questionnaires were anonymous. Among the student-teachers, 17.2% reported current voice complaints in comparison with 9.7% of the reference group, and the odds ratio was 1.94, which showed the relative risk. Student-teachers had significantly greater total Voice Handicap Index (VHI) scores than the reference group (P = 0.034). The VHI subscale scores were not significantly different (P > 0.05). Student-teachers who reported current voice complaints had a significantly higher total VHI and subscale scores than student teachers without voice complaints (P < 0.001). Of the student-teachers without voice complaints, 17.0% had VHI scores greater than the 75th percentile. These persons may be neglecting their voice handicap and probably represent the false-negative cases in the estimation of voice complaints. Logistic regression analysis of each of the given risk factors with the VHI as the independent variable showed that the perceived negative influence of the given risk factors on their voices was significantly greater with increasing VHI scores across the VHI range. A significant correlation was observed between the number of perceived risk factors and increasing VHI scores across the VHI range. An increased awareness of risk factors in relation to their voice handicap would serve to motivate student-teachers to change factors that contributed to their voice problem. Attention to all risk factors, which the subjects perceive to be a risk, would aid in effective management of their voice handicap.     

A note on compactness in Banach spaces

Two simple concepts are presented for constructing necessary and sufficient compactness criteria in Banach spaces. The concepts are applied to the spaces lip(T), C(T), and L_p(µ), where T is a compact metric space.     

The pulsed optogalvanic effect in a low-pressure mercury discharge

Experiments are described in which a low-pressure mercury discharge is irradiated with a 10 ns dye laser pulse tuned resonant to one of 6 ³P-7 ³S₁ transitions. The time behaviour of the induced optogalvanic effect is found to be dependent on the value of the ballast resistance in the discharge circuit. The qualitative explanation for this phenomenon is that the ratio of the relative change in the electron temperature and the relative change in electron density depends on the value of the ballast resistance.