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[Which definition to use when defining airflow obstruction?].

INTRODUCTION
There is no clear consensus as to what constitutes an obstructive ventilatory defect (OVD). According to the American Thoracic Society and European Respiratory Society, it is defined as being when the ratio of the forced expiratory volume (FEV1) and the slow expiratory vital capacity (VC) is below the lower limit of normal (LLN). According to the Global initiative for chronic Obstructive Lung Disease and the British Thoracic Society, it is an FEV1/forced expiratory vital capacity (FVC)<0.70 and an FEV1<80%. In addition, in daily practice, the OVD is diagnosed by a "Fixed ratio" FEV1/FVC<0.70 or<LLN. The aim of this study is to determine, according to the different recommendations, the percentage of subjects having an OVD among them addressed for suspicion of chronic obstructive pulmonary disease.


METHODS
A medical questionnaire was administered and anthropometric data were collected. The expiratory flows and pulmonary volumes were measured by a body plethysmograph.


RESULTS
121 (81%) subjects among the 150 examined were included. The percentage of subjects having an OVD was 56.1% (FEV1/VC<LLN), 54.1% (FEV1/FVC<0.70), 48.7% (FEV1/FVC<0.70 and FEV1<80%), and 47.8% (FEV1/FVC<LLN).


CONCLUSION
The prevalence of obstructive ventilatory defect in a population depends on the definition chosen.