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R F Leonard

Publications and source records attributed to R F Leonard.

At least 19 recordsLinked to original sources
PubMed1999

A critical evaluation of the Mefar dosimeter.

Multicentre studies of airway responsiveness (AR) are increasingly important tools in asthma epidemiology. Because comparisons of AR are made between centres it is essential that measurement techniques are accurate and standard. This study investigated the Mefar dosimeter which is currently used in the 35 centre European Community Respiratory Health Survey (ECRHS) with the next phase currently being planned. Significant differences were found in driving pressures and aerosol outputs between the three Mefar dosimeters in the laboratory. A linear relationship was also found between driving pressure and aerosol output (R2=0.96). These differences are important as they may lead to variations between centres of < or =35% in the drug dose delivered in AR measurement, which could potentially diminish the power of individual study centres to accurately detect national differences in AR. Dosimeter driving pressure and nebulizer output should be standardized in future studies of airway responsiveness. With relatively simple quality control measures in place it is believed that the Mefar dosimeter can produce reliable between-centre longitudinal data with an increase in the accuracy of these important studies.

Aerosols↗
PubMed1998

Nebulizer calibration using lithium chloride: an accurate, reproducible and user-friendly method.

Conventional gravimetric (weight loss) calibration of jet nebulizers overestimates their aerosol output by up to 80% due to unaccounted evaporative loss. We examined two methods of measuring true aerosol output from jet nebulizers. A new adaptation of a widely available clinical assay for lithium (determined by flame photometry, LiCl method) was compared to an existing electrochemical method based on fluoride detection (NaF method). The agreement between the two methods and the repeatability of each method were examined. Ten Mefar jet nebulizers were studied using a Mefar MK3 inhalation dosimeter. There was no significant difference between the two methods (p=0.76) with mean aerosol output of the 10 nebulizers being 7.40 mg x s(-1) (SD 1.06; range 5.86-9.36 mg x s(-1)) for the NaF method and 7.27 mg x s(-1) (SD 0.82; range 5.52-8.26 mg x s(-1)) for the LiCl method. The LiCl method had a coefficient of repeatability of 13 mg x s(-1) compared with 3.7 mg x s(-1) for the NaF method. The LiCl method accurately measured true aerosol output and was considerably easier to use. It was also more repeatable, and hence more precise, than the NaF method. Because the LiCl method uses an assay that is routinely available from hospital biochemistry laboratories, it is easy to use and, thus, can readily be adopted by busy respiratory function departments.

Aerosols↗
PubMed1994

True Blue.

Explore the source record for details and available documents.

Drama↗
PubMed1991

Measuring blood cholesterol outside the pathology laboratory: issues of accuracy and reliability.

Desk-top analysers that are simple to use, portable and free from technical requirements are now widely used for blood cholesterol measurement outside the traditional pathology laboratory setting. Test accuracy and reliability are essential if these portable desk-top analysers are to be of value in the assessment and management of elevated blood cholesterol. To determine their accuracy and reliability we compared the results obtained from four different desk-top analysers with those from a teaching hospital's routine laboratory method. The desk-top analysers assessed were the Ames Minilab, the Kodak DT60, the Boehringer Reflotron and the Abbott Vision. The precision of each desk-top analyser was within acceptable limits, defined as a coefficient of variation less than 5 per cent. The results from the Vision, Reflotron and DT60 related closely to those from routine laboratory method, with least squares linear regression slopes ranging from 0.92 to 1.06 and intra-class correlation coefficients from 0.95 to 0.99. The Minilab showed least agreement with the routine laboratory method and caution should be taken in the interpretation of cholesterol estimations made with this device.

Blood Chemical Analysis↗
PubMed1986

Combined phenytoin and salicylate effects on thyroid function tests.

To evaluate the effects of salicylates (ASA) on thyroid function tests (TFT's) in patients already taking phenytoin (DPH), 6 adults received a daily dose of DPH to achieve a steady state serum DPH. ASA was then added stepwise (325, 650, 975 mg q 4hr) at 2-day intervals. TFTs, total serum and free salivary DPH were measured. Therapeutic steady state phenytoin levels caused a significant decrease in serum free thyroxine (FT4), total T4, total T3 (TT3) and a significant but slight increase in T3RU. The TSH remained normal. When ASA was co-administered with DPH, the serum free DPH increased, the total T4, TT3, FT4 significantly decreased further, and the T3RU significantly declined toward pre-treatment levels. The decrease of FT4 was in contrast to the increase in FT4 known to occur with ASA alone. Despite the decline in total T4, TT3, and FT4, the TSH remained normal. In conclusion, when ASA is co-administered with DPH, further alterations in TFTs occur which require cautious interpretation. Our in vivo and in vitro data show that these changes are consistent with ASA-induced displacement of T4 from its binding proteins and DPH-induced clearance of FT4.

Aspirin↗
PubMed1981

Phenytoin-salicylate interaction.

Ten healthy adult subjects took a single daily dose of phenytoin for 9 days to achieve a steady-state serum phenytoin concentration in the therapeutic range. While continuing on phenytoin, subjects took increasing doses of salicylate in a step-wise fashion, each dose (325, 650, and 975 mg) given every 4 hr for 48 hr. Serum (total) and salivary (free) phenytoin concentrations and serum salicylate concentrations were measured before and after each dose level of salicylate. Protein binding displacement of phenytoin by salicylate occurred only at the highest salicylate dose. Serum phenytoin control levels fell from 13.5 +/- 1.2 to 10.3 +/- 0.8 micrograms/ml (p less than 0.01), salivary phenytoin levels rose from 0.97 +/- 0.09 to 1.13 +/- 0.12 micrograms/ml (p less than 0.05), and phenytoin free fraction (salivary/serum ratio) increased from 7.14 +/- 0.34% to 10.66 +/- 0.57% (p less than 0.01) in the highest salicylate dose periods. There was no difference in these parameters during low-dose or intermediate-dose salicylate therapy. Linear-regression analysis failed to show a relationship between serum salicylate concentration and serum or salivary phenytoin concentration. Although high-dose salicylate induced protein binding displacement of phenytoin, it is unlikely that this is of clinical importance since the rise (16%) in the free (salivary) phenytoin concentration was small. Serum total phenytoin concentration may fall during salicylate therapy but the dose of phenytoin should not be altered unless there are overt signs of toxicity.

Adult↗