A second-generation constrained reaction volume shock tube.

We have developed a shock tube that features a sliding gate valve in order to mechanically constrain the reactive test gas mixture to an area close to the shock tube endwall, separating it from a specially formulated non-reactive buffer gas mixture. This second-generation Constrained Reaction Volume (CRV) strategy enables near-constant-pressure shock tube test conditions for reactive experiments behind reflected shocks, thereby enabling improved modeling of the reactive flow field. Here we provide details of the design and operation of the new shock tube. In addition, we detail special buffer gas tailoring procedures, analyze the buffer/test gas interactions that occur on gate valve opening, and outline the size range of fuels that can be studied using the CRV technique in this facility. Finally, we present example low-temperature ignition delay time data to illustrate the CRV shock tube's performance.

Parkinson's disease: the effect of L-dopa therapy on urinary free catecholamines and metabolites.

BACKGROUND: L-dopa is an important antiparkinsonian drug. It is a precursor of dopamine and the other catecholamines. Potentially, administration of L-dopa could lead to increased urinary excretion of catecholamines and their metabolites to abnormal amounts. The current study aimed to determine these excretions in patients with Parkinson's disease (PD) receiving L-dopa compared with suitable controls. This is the first assessment of the effect of exogenous administration of L-dopa on urinary free metadrenalines. METHODS: Using one-way analysis of variance (ANOVA), urine catecholamines and metabolites, expressed as mmol per mole creatinine, were compared in: patients with PD who were receiving L-dopa; patients with PD but not receiving L-dopa; and patients without PD who were being investigated for the presence of phaechromocytoma but were found not to have the disease. RESULTS: Significantly higher values for urinary dopamine, homovanillic acid, free normetadrenaline and free metadrenaline were found in patients with PD receiving L-dopa compared with the other two control groups. In all the patients with PD, these four analytes were significantly correlated with daily dose of L-dopa. CONCLUSION: L-dopa therapy can result in production of false positives for urinary excretion of dopamine, homovanillic acid, free normetadrenaline or free metadrenaline and thereby decrease the diagnostic value of these measurements in identifying phaeochromocytoma and related tumours.

EDTA analysis on the Roche MODULAR analyser.

BACKGROUND: Patient specimens can be subject to subtle interference from cross contamination by liquid-based, potassium-containing EDTA anticoagulant, leading to misinterpretation of results. A rapid method for EDTA analysis to detect such contamination is described. METHOD: An in-house EDTA assay on the Roche MODULAR analyser was assessed for accuracy and precision by comparison with an adjusted calcium difference measurement (atomic absorption and o-cresolphthalein complexone colorimetry). RESULTS: EDTA method versus adjusted calcium difference showed: slope = 1.038 (95% confidence interval [CI] 0.949-1.131); intercept = 0.073 (95% CI 0.018-0.132) mmol/L; r = 0.914; n = 94. However, inter-assay precision of the calcium difference method was estimated to be poorer (coefficient of variation 24.8% versus 3.4% for the automated colorimetric method at an EDTA concentration of 0.25 mmol/L). Unequivocal contamination was observed at an EDTA concentration of > or =0.2 mmol/L. The automated method showed positive interference from haemolysis and negative interference from oxalate. The method was unaffected by lipaemia (triglycerides <20 mmol/L), icterus (bilirubin <500 micromol/L), glucose (<100 mmol/L), iron (<100 micromol/L), and citrate, phosphate or fluoride (all <2.5 mmol/L). CONCLUSION: The automated colorimetric assay described is an accurate, precise and rapid (3 min) means of detecting EDTA contamination of unhaemolysed biochemistry specimens.

Shock-tube study of high-pressure H2O spectroscopy.

Water-vapor absorption features near 7117, 7185, and 7462 cm(-1) were probed at pressures to 65 atm (1 atm = 760 Torr) and temperatures to 1800 K in shock-heated mixtures of H(2)O in N(2) and Ar with a diode-laser source. Calculated absorbances based on Voigt line shapes and measured line parameters were in good agreement, within 10%, with measured absorbances at 7185.4 and 7117.4 cm(-1). We obtained temperature-dependent N(2) and Ar shift parameters for H(2)O absorption features by shifting the calculated spectra to match the recorded absorption scan. Absorbance simulations based on line parameters from HITRAN and HITEMP were found to be similar over the range of temperatures 600-1800 K and were within 25% of the measurements. The combined use of Toth's [Appl. Opt. 36, 4851 (1994)] line positions and strengths and HITRAN broadening parameters resulted in calculated absorption coefficients that were within 15% of the measurements at all three probed wavelengths.

Observations on the relationships between plasma free fatty acids, ketones and bicarbonate in acute hyperglycaemia.

Some of the initial biochemical findings, obtained from 141 randomly-selected cases of acute hyperglycaemia (admission plasma glucose > 20 mmol/L) were examined. When viewed in terms of their initial plasma bicarbonate concentration, three groups were identifiable. Plasma concentrations of free fatty acids (FFA), acetone and the sum of 3-hydroxybutyrate (3OHB) and lactate were different between these groups. However, there were no differences in plasma glucose or lactate concentrations. It was further observed that the relationship between the plasma FFA/albumin molar ratio, and ketone concentration could be described by a rectangular hyperbola, and the initial anion gap was linearly related to the sum of the 3OHB and lactate concentrations.

The Gluma bonding system: a clinical evaluation of its various components for the treatment of hypersensitive root dentin.

This study investigated the desensitizing effect of topically-applied Gluma on sensitive cervical erosion lesions. A total of 46 teeth exhibiting moderate to severe sensitivity to cold and instrumentation, in 15 patients, were included in the study. Mildly sensitive teeth and teeth with cervical caries lesions were excluded from the study. After each tooth was isolated with rubber dam, investigators applied cold air, as well as tactile stimuli using an explorer, and recorded the baseline responses. Nine of the 46 teeth then received Gluma primer only (group 1), 15 received cleanser followed by primer (group 2), 15 received cleanser followed by primer and sealer (group 3), and seven received a placebo (group 4). After two weeks, the teeth in group 4 were randomly placed in one of the other three groups. The responses of the teeth in each group to various stimuli were recorded immediately after the application of test materials, and subsequently at one week, two weeks, one month, three months, six months and one year. Statistical analysis indicates that the three treatment groups all showed significant differences compared to the untreated control group (p < .001). A reduction of sensitivity was noted immediately after primer, cleanser-primer, or cleanser-primer-sealer was applied. Treatment groups 2 and 3 demonstrated less sensitivity than group 1 (p = .02; p = .03, respectively). At the one-year recall, the observed order of treatment effectiveness by group was 2, 3, 1. In approximately 50 per cent of the teeth treated in the study, remission of sensitivity was seen after one year. All of the remaining teeth exhibited some relief of sensitivity. The treatments' success was found to be inversely proportional to the severity of the initial response.

Development of indices for determining extracellular fluid sodium and water status in acute diabetic ketoacidosis: possible tools for clinical audit.

The limitation of plasma sodium concentration as an indicator of extracellular hydration status in cases of acute diabetes is well recognized and could lead to individually inappropriate fluid therapy. However, in view of the small analytical and biological variations exhibited by plasma concentrations of protein, water, and sodium in health, we have developed simple laboratory indices that may better describe the extracellular environment. Preliminary data presented here for 20 patients with acute diabetic ketoacidosis admitted as emergencies to Crosshouse Hospital suggest that the type of approach we describe has the potential to supply meaningful therapeutic data to the managing physician and, therefore, merits further study in a clinical setting.

Clinical evaluation of a universal dentin bonding resin: preserving dentition through new materials.

The new generation of dentin bonding materials can withstand the contraction shrinkage of composite materials. A two-year clinical trial of one material showed an excellent retention rate.

Inaccuracy of osmometry for measurement of plasma water in acute diabetes mellitus.

Osmometry is reportedly a relatively imprecise technique for the measurement of plasma water. However, reconsideration of the theoretical background of the test reveals that it is also likely to be inaccurate and subject to both positive errors as well as viscosity-dependent negative errors simultaneously, when applied to samples from patients admitted in acute diabetes mellitus. This was confirmed by comparison with Waugh's method of results for 59 specimens from 14 cases. Plasma water was shown to be relatively underestimated at high protein concentrations and overestimated at lower ones.

Excess osmolal gap in diabetic ketoacidosis explained.

Even in the absence of detectable ethanol or visible lipemia, a large plasma osmolal gap is the usual finding in cases of diabetic ketoacidosis. This gap decreases to an insignificant value within 20 h of treatment. Detailed biochemical analysis of six cases showed that, on average, the gap could be almost wholly accounted for by an increase in acetone, a decrease in the plasma water fraction, and smaller increments in amino acids and glycerol. Calculated plasma osmolality can seriously underestimate the true value in diabetic ketoacidosis, and so some previously observed anomalies may be explained.

Continuous wave laser absorption techniques for gasdynamic measurements in supersonic flows.

Line-of-sight measurements of velocity, temperature, pressure, density, and mass flux were performed in a transient shock tube flow using three laser absorption schemes. All methods employed an intracavity-doubled ring dye laser tuned to an OH transition in the A(2) summation operator(+) ? X(2)II (0,0) band at 306 nm. In the first scheme, the gas was labeled by 193.3-nm excimer photolysis of H(2)O, and the passage of the generated OH was detected downstream. In the second method, the laser was tuned at a rate of 3 kH(z) over the R(1)(7) and R(1)(11) line pair, and absorption was simultaneously monitored at 90 and 60 degrees with respect to the flow. Velocity was determined from the Doppler shift of the profiles and the temperature from the intensity ratio of the lines. Pressure was determined from both the magnitude of absorption and the collisional broadening. In the third method, the laser wavelength was fixed at a single frequency, and a continuous measurement of velocity and pressure was obtained using the signals from the two beam paths. All methods gave results which compare favorably to calculated values.

Rapid tuning cw laser technique for measurements of gas velocity, temperature, pressure, density, and mass flux using NO.

An intracavity-doubled rapid-tuning cw ring dye laser was used to acquire fully resolved absorption profiles of NO line pairs in the A ? X band at 225 nm at a rate of 4 kHz. These profiles were utilized for simultaneous measurements of flow parameters in the high speed 1-D flows generated in a shock tube. Velocity was determined from the Doppler shift measured using a pair of profiles simultaneously acquired at different angles with respect to the flow direction. Temperature was determined from the intensity ratio of the adjacent lines. Pressure and density were found both from the collisional broadening and the fractional absorption. From this information the mass flux was determined. The results compare well to 1-D shock calculations.

The development of computer programs to predict and minimise the effect of sample pyruvate on aspartate aminotransferase assays.

Some NADH-linked aspartate aminotransferase (AST) assay systems may produce significant errors due to endogenous pyruvate because the pre-incubation time employed is too short and/or because the reagent lactate dehydrogenase (LD) activity is inadequate. Such errors in patient specimens may go unnoticed if quality control materials themselves contain a low pyruvate concentration. A theory of pyruvate interference in AST assay is formulated and calculation programs are described which will allow a laboratory to assess whether their particular AST methods are likely to be subject to such interference and also to predict a way of removing any error thus identified.

Simultaneous assay for urinary 4-hydroxy-3-methoxy-mandelic acid, 5-hydroxyindoleacetic acid and homovanillic acid by isocratic HPLC with electrochemical detection.

A method is described for the simultaneous determination of urinary HMMA, 5-HIAA and HVA by HPLC with electrochemical detection. The method was evaluated over an 8-month period and has thus far identified 2 cases of phaeochromocytoma, 1 case of neuroblastoma and 2 of carcinoid tumour.