[Evaluation and follow up of hyperinflation in COPD]

Plethysmography is the reference method and requires rigorous methodology, particularly in patients with severe airflow limitation. Dilution techniques (nitrogen or most often helium) may underestimate true lung volumes as they do not measure trapped gas. Inspiratory capacity is the only available method to evaluate exercise induced dynamic hyperinflation. It is an imperfect surrogate of plethysmography for evaluating the reversibility of hyperinflation with bronchodilators. Resting hyperventilation has recently been shown to be a sensitive method to detect dynamic hyperinflation. Evaluation of hyperinflation is an important criterion in the phenotyping of COPD patients. However, its natural history remains at present poorly defined.