Response

We thank Leong and colleagues for their comments regarding our manuscript1 and for highlighting the role of the central airways in modulating pressure and airflow in patients with a label of ‘obstructive airways disease’.2 We agree that a functional role of the glottis may indeed be to regulate and interact with excessive dynamic airway narrowing.

Their group have previously highlighted the utility of a 320-slice CT imaging protocol in characterising the high prevalence of laryngeal closure in patients with severe asthma,3 and thus this and other novel CT techniques4 certainly have the potential to enlighten us regarding the interaction between laryngeal and large airway movement in obstructive airways disease. Nevertheless, while acknowledging this work, several limitations of these techniques exist, including the recurrent use of ionising radiation, inherent difficulties in gathering a prolonged period of data and collecting data under the setting of relevant physiological stress, that is, exercise, or indeed even in the upright position.

Moreover, we feel that caution, and likely further data, is needed when considering the degree to which large airway narrowing should be classified as ‘excessive’. Some reports indicate that over half of any asymptomatic cohort may reduce tracheal dimensions to 50% during a dynamic manoeuvre and thus more conservative estimates (eg, >90% narrowing) may be appropriate.5

Regardless, the interaction between the larynx and large central airways is certainly in need of further investigation if to enlighten us regarding the physiological basis of the pervasive and debilitating exertional limitation that exists in chronic obstructive lung disease.6