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Copyright ©ERS Journals Ltd 2002
European Community Respiratory Health Survey calibration project of dosimeter driving pressures
1 Dept of Psychiatry, University of Melbourne, Victoria, Australia, 2 William Leech Cardiothoracic Centre, University of Newcastle upon Tyne, UK, 3 Dept of Medicine, University of Tasmania Medical School, Hobart, 4 Dept of Respiratory Medicine and 5 Epidemiology and Preventive Medicine, Alfred Hospital and Monash University Medical School, University of Melbourne, Victoria, Australia
CORRESPONDENCE: E.H. Walters, Dept of Medicine, University of Tasmania Medical School, Hobart, Australia. Fax: 61 362264894
Keywords: dosimeters, driving pressure, European Community Respiratory Health Survey
Received: March 9, 2001
Accepted October 12, 2001
Two potential sources of systematic variation in output from Mefar dosimeters, the system used in the European Community Respiratory Health Survey (ECRHS) study have been evaluated: individual nebulizer characteristics and dosimeter driving pressure.
Output variation from 366 new nebulizers produced in two batches for the second ECRHS were evaluated, using a solute tracer method, at a fixed driving pressure. The relationship between dosimeter driving pressure was then characterized and between-centre variation in dosimeter driving pressure was evaluated in an Internet-based survey.
A systematic difference between nebulizers manufactured in the two batches was identified. Batch one had a mean±sd output of 7.0±0.8 mg·s–1 and batch two, 6.3±0.7 mg·s–1 (p<0.005). There was a wide range of driving pressures generated by Mefar dosimeters as set, ranging between 70–245 kPa, with most outside the quoted manufacturer's specification of 180±5%. Nebulizer output was confirmed as linearly related to dosimeter driving pressure (coefficient of determination (R2)=0.99, output=0.0377xdriving pressure–0.4151). The range in driving pressures observed was estimated as consistent with a variation of about one doubling in the provocative dose causing a 20% fall in forced expiratory volume in one second.
Systematic variation has been identified that constitutes potentially significant confounders for between-centre comparisons of airway responsiveness in the European Community Respiratory Health Survey, with the dosimeter driving pressure representing the most serious issue. This work confirms the need for appropriate quality control of both nebulizer output and dosimeter driving pressure, in laboratories undertaking field measurements of airway responsiveness. In particular, appropriate data on driving pressures need to be collected and factored into between-centre comparisons. Comprehensive collection of such data to optimize quality control is practicable and has been instigated by the organizing committee for the European Community Respiratory Health Survey II.
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