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What is True about the chronic obstructive pulmonary disease (COPD) and explain in detail?
In COPD, airflow obstruction is demonstrated by spirometry in which the post-bronchodilator FEV1/FVC is less than 70%. 
The severity of COPD may be defined in relation to the post-bronchodilator FEV1 which is <30% predicted in very severe type. 
Measurement of lung volumes provides an assessment of hyperinflation.COPD is characterised by an increase in residual volume, residual volume/total lung capacity ratio, and progressive hyperinflation(increased total lung capacity) late in the disease.