Deep breaths and airway obstruction in asthma.

Spontaneously obstructed asthmatics constrict their airways after a DI. Such behavior is also seen in chronic bronchitis in which there is a prominent inflammatory component. Induced obstruction is reversed by a deep breath in asthmatic and chronic bronchitic patients and probably represents constriction of smooth muscle in conducting airways to give a predominance of airway hysteresis. Bronchodilation results in a constrictor effect of a DI which probably represents relaxation of smooth muscle in conducting airways, thereby decreasing airway hysteresis and allowing parenchymal hysteresis to dominate. As can be appreciated in Figure 3, all possible responses to a DI are seen and become coherent within the framework of the relative hysteresis analysis. The response of airways to a deep breath may relate to both site and mechanism of obstruction. It is suggested that defining the airway response to a deep breath in an asthmatic may relate not only to site and mechanism but may dictate what therapeutic agents should be given at that time.