Exhaled nitric oxide is increased in asthma.

and the lack of a response to hyperventilation, may not relate to asthma so much as they relate to disease severity or patient age. Finally, changes in responsiveness induced by allergen stimulation are not related to baseline AHR. This suggests that chronic persistent AHR may have underlying mechanisms that differ from those responsible for short-term changes in AHR induced by inflammation. Our ability to clarify these issues and to better define the structure-function correlates of AHR will depend on our ability to obtain and investigate airway tissue from humans with well-characterized clinical abnormalities.