chapter  7
Airway responsiveness
Pages 6

Although hyperresponsiveness has been recognized to be a characteristic of COPD for some time, the question of whether it is a true risk factor (i.e. predates the onset of COPD) or results from the disease process itself has been intensely controversial. Cross-sectional studies, of which there have been many, are unable to disentangle the causal chain in this complex relationship.