The direct and indirect action of inhaled agents on the lung and its circulation: lessons for clinical science.

Inhalation of particles, gases, and vapors from environmental pollution results in a number of localized and general responses by the lungs. In this article we report investigations performed in humans that have enabled the identification of these specific processes in response to inhaled materials. We also offer insights that could help generalize environmental inhaled pollutants and potential means of studying them in humans. Three specific areas are covered: impact of denervation of the lungs and airway inflammation on the acute defense mechanism of the lungs to inhaled "irritants," differential uptake of inhaled particles into separate regions of the lungs, and the effect of inhaled nitric oxide on pulmonary vasculature and gas exchange. The inhalation of nitric oxide reflects the potential of inhaled pollutants to influence gas exchange, especially in patients with established lung disease, such as chronic obstructive pulmonary disease.