The quality of home spirometry in school children with asthma.

BACKGROUND Handheld electronic spirometers provide the opportunity for more comprehensive monitoring of lung function at home than has hitherto been available. The aim of this study was to assess the quality of spirometric data collected at home by 90 asthmatic schoolchildren aged 7-14 years. METHODS After training, children carried out twice daily recordings at home for four consecutive periods of 4 weeks using a data storage spirometer (Vitalograph), encouraged by 4-weekly visits from a research nurse. Compliance (proportion of blows recorded at correct time of day), technical quality (by machine criteria), and valid data recorded (the multiple of compliance and technical ability) were assessed. RESULTS Mean compliance declined from 81.4% to 70.4% (p<0.001) between the first and last month, although the technical quality of the manoeuvres (81.9% and 80.1%, respectively) did not change significantly (p=0.48). CONCLUSIONS There was a steady reduction of valid data over the four periods (from 73.6% to 64.3%, 59.7%, and 57.6%) with wide individual differences. Even under ideal conditions, home spirometry provides an incomplete (and therefore potentially biased) picture of long term changes in pulmonary function.