The European Community Respiratory Health Survey II.
The European Community Respiratory Health Survey (ECRHS) II is a multicentre study that includes assessment of bronchial responsiveness using the Mefar dosimeter (Mefar, Brescia, Italy). WARD et al. [1] report that in some centres taking part in ECRHS II, there is potential for systematic variation in Mefar dosimeter driving pressure, which constitutes possible significant confounding for between-centre comparisons of bronchial hyperresponsiveness. They reported a wide range of driving pressures between centres "ranging between 70–245 kPa, with most outside the quoted manufacturer9s specification of 180¡5%". WARD et al. [2] drew our attention to this problem when we were developing the quality control programme for ECRHS II. All ECRHS II centres were requested to check dosimeter driving pressure at least once a month and to send reports to the Coordinating Centre. Where readings were v160 kPa or w180 kPa, centres were advised to adjust the dosimeter to a level within these limits. R.J. Ward and his group set up a website with instructions on how this could be achieved, together with information on the testing procedure. Reports were received from all centres except for Umea (Sweden) and showed that no centre recorded a level v160 kPa and the highest value was 200 kPa, found in Hamburg (Germany). In Hamburg, alterations were made to the equipment and it operated aty180 kPa for the rest of the study. The mean pressure for centres throughout the study ranged 160 kPa–189 kPa (Hamburg had a higher mean due to its driving pressure being 200 kPa for a period). Although table 1 of the paper concerned [1] implies a substantial problem within the participating European Community Respiratory Health Survey II centres, the quality control programme reveals that although variation exists, the magnitude and its influence on between-centre comparisons is much smaller than suggested by WARD et al. [1] in their recent paper.