Biomedical subjects

A A Gatnash

Publications and source records attributed to A A Gatnash.

3 recordsLinked to original sources

PubMed1998

A new method for measuring aerosol nebulizer output using radioactive tracers.

Reproducibility and comparability of bronchial challenge tests depends critically on accurate assessment of nebulizer output. Evaporation during nebulization means that simple weighing is inaccurate, overestimating the delivered dose of active ingredient. We wanted to quantify this effect in the context of intermittent nebulization, using a dosimeter as used in bronchial provocation tests. Output of three types of nebulizer, from the MEFAR dosimeter, was measured by radioactive tracer, using a standard solution of technetium-99m-pertechnetate (1.5 kBq x mL(-1)) in 4 mL of normal saline. The aerosol was impacted by suction onto a microfilter, and the radioactivity measured. Nebulizers were weighed before and after nebulization. Ratio of nebulized volume calculated from the radioactivity on the filter, to the total volume loss by weight, was expressed as nebulized ratio. The effect on output of two concentrations of methacholine, two tracers of different weights, and change in temperature, were assessed. Nebulized ratio varied between 44.1-71.6%. Results were more consistent within the same type of nebulizer than between different makes. Neither changes in molar concentration nor molecular weight affected nebulizer output or nebulized ratio. Mean nebulized ratio was 58.5%, showing that calibration by weighing, overestimates the delivered dose by a factor of approximately two. Measuring radioactivity eluted from a microfilter, onto which nebulized output had been impacted proved to be a satisfactory method of calibration.

Aerosols↗

PubMed1995

Fatal chickenpox pneumonia in an asthmatic patient on oral steroids and methotrexate.

A 49 year old man with a long history of severe chronic asthma, treated with oral corticosteroids and weekly doses of methotrexate, contracted chickenpox from his son whose chickenpox rash had developed three weeks before presentation. Five days before admission the patient developed a vesicular skin rash which became extensive, with general malaise, bilateral pneumonia, and acute deterioration of his asthma. He died two weeks after admission despite treatment with acyclovir.

Acyclovir↗

PubMed1994

Actual over best function as an outcome measure in asthma.

Several guidelines for the management of asthma suggest that actual/best function is a useful outcome measure. This implies accurate assessment of best function, and a standard for the proportion of best function to be achieved. Seventeen clinics observed their practice simultaneously during four periods in 1990. The aims of the study included testing a protocol for the assessment of best function, and validating actual/best function as an outcome measure. The proposed target for actual/best function to indicate satisfactory control was 80%. The protocol for assessment of best function required formal trial of steroids if best function was < 70% predicted; with regular recording of peak expiratory flow (PEF) if < 80% predicted. PEF was recorded in 515 and FEV1 in 680 of 767 subjects, following the usual clinic practice. If the protocol for best function was not satisfied, mean actual/best function was no higher than if it was, except when best PEF was < 70% predicted. This suggests the need for a PEF chart in these latter patients. Best function was greater in females than males, but actual/best function was almost identical. Whilst best function declined with increasing intensity of treatment, actual/best function was almost independent of regimen step, particularly in the centre which most closely adhered to the protocol. These results confirm that actual/best function is a valid outcome measure. Mean actual/best was > 80% except for FEV1 in two centres. It is suggested that the target in chronic management of asthma is raised from 80 to 85% of best, when actual/best PEF is used as a spot check in patients believed to be on optimal therapy.

Asthma↗