The cholinergic reflex plays a role in the acute bronchoconstrictive response to the inhalation of irritants. Recent interest in neurogenic mechanisms of asthma have focused on neuropeptides that are secreted by sensory nerves. These substances have vascular permeability and mucus secretory activity, bronchoconstrictor activity, and a bronchial vascular dilation effect. These cause narrowing of the airway and increased resistance to airflow. The chest x-ray changes seen in these patients include hyperlucency of the lung fields and hyperinflation characterized by wide intercostal spaces and flattened diaphragm.
Symptoms can develop slowly, or suddenly and unexpectedly, creating great distress.
Dyspnea or difficult breathing is the predominant symptom and may be the most common reason patients seek urgent care. Dyspnea was found to be related to demographic variables in a predictive model of dyspnea in asthmatics. Investigations of the role of dyspnea and associated respiratory sensations in mediating the outcomes of other chronic pulmonary conditions show that episodes of increased dyspnea severity have large, independent effects on the quality of life and functional status in people with chronic obstructive pulmonary disease. It has been assumed that the same may be true for people with asthma, but this assumption has not been tested. Only aspects of acute dyspnea in asthma have been reported.