Cough: physiology, evaluation, and treatment.

Abstract

Cough is one of a group of defensive respiratory reflexes. The reflex is a complex one, with the afferent pathway within the vagus nerve, and the efferent pathway within the somatic nervous system. Cough receptors are situated mainly but not exclusively within the extrapulmonary airways. Several types of afferent nerves may subserve the cough reflex, including both myelinated and nonmyelinated fibers. The cough efferent response involves vigorous motor activity with generation of high intrathoracic pressure, high flows at the mouth, and high intrathoracic gas velocities. In addition to the advantageous effects of cough are deleterious consequences including chest wall trauma and hemodynamic disturbance. Evaluation of cough may employ a simplified model of cough pathogenesis wherein abnormalities of the lungs are sought. A more complex model is also appropriate, which allows for the possibility that cough may result from abnormalities outside of the lungs. Conclusions drawn from evaluations employing the latter model tend to be tentative and treatment needs to be appropriate to the degree of impairment and the level of certainty as to the causal nature of the associations. When a cause for cough cannot be found, treatment with nonspecific antitussives is indicated. Codeine, dextromethorphan, and diphenhydramine have been recommended as safe and effective therapies.