Asthma and airway hyperresponsiveness.

Airway hyperresponsiveness to a large number of stimuli is a characteristic of asthma in humans. Various components of the tracheobronchial tree might contribute to this characteristic, such as smooth muscle, the bronchial epithelium, various neurohumoral mechanisms, and the mechanical linkages between the lung parenchyma and the airways. The degree of responsiveness can be further increased by a series of stimuli associated with inflammation in the periphery of the lung. Such stimuli actually induce an asthmatic state or heighten the vulnerability of asthmatics, making them more prone to overt attacks in response to minor stimuli that would ordinarily be well tolerated. Depending upon the inciting stimulus, different cells and mediators may be playing a role in producing and perpetuating the inflammatory state and producing further increases in responsiveness.