The GOLD (Global initiative for chronic Obstructive Lung Disease) is a classification of severity of airflow limitation in COPD based on post-bronchodilator forced expiratory volume in one second (FEV1) and the forced vital capacity (FVC) [ 1].
Bronchodilator response in patients with asthma is evaluated based on post-bronchodilator increase in forced expiratory volume in one second (FEV1) and forced vital capacity (FVC).
Patients were classified into GOLD stage 2 to 4, based on post-bronchodilator FEV1% predicted 50-700%, 30-50%, <30%) and into GOLD stage A to D, based on the 2013 GOLD classification [ 8].
The criteria of recruitment were patients aged over 40 years with a diagnosis of COPD based on post-bronchodilator ratio of FEV1/FVC < 0.7 in the past 6 months, smokers or ex-smokers with a smoking history of more than 10 pack-years, and no history of acute exacerbation for at least three months prior to the enrollment.
In a population-based study using the Burden of Obstructive Lung Disease (BOLD) survey, close to 100 cases of COPD were identified based on post-bronchodilator spirometry and they found no increased risk for self-reported cardiovascular disease or hypertension in either of the GOLD-stages [ 30].
This group (n= 1,578) was divided into three groups (tertiles) based on their post-bronchodilator FEF50%percentt predicted, in order to select patient populations with and without probable SAD.
Following the traditional practice of considering irreversible airflow limitation to be COPD, the COPD diagnosis was strictly based on the post-bronchodilator lung function criteria without requiring documented exposure to a known causative agent.
Controls with COPD, based on pre-bronchodilator spirometry (GOLD stage 1 or more), who constituted 35% of the smoking volunteers, were excluded from further analysis.
Subjects recruited into the study were aged 40 80 yrs, with a minimum smoking history of 20 pack-yrs and COPD confirmed by a respiratory specialist based on pre-bronchodilator spirometric criteria (GOLD stage 2 or more).
The GLI reference values are based on pre-bronchodilator values, and only pre-bronchodilator values from the reference population were collected and analysed.
