Nitric oxide in the nasal airway: A new dimension in otorhinolaryngology

The discovery that the gas nitric oxide (NO) is an important signaling mole cule in the cardiovascular system earned its Nobel prize in 1998. NO has si nce been found to play important roles in a variety of physiologic and path ophysiologic processes in the body including vasoregulation, hemostasis, ne urotransmission, immune defense, and respiration. The surprisingly high concentrations of NO in the nasal airway and paranasa l sinuses has important implications for the field of otorhinolaryngology. NO provides a first-line defense against micro-organisms through its antivi ral and antimicrobial activity and by its upregulation of ciliary motility. Nasal treatments such as polypectomy, sinus surgery, removal of hypertroph ic adenoids and tonsils, and treatment of allergic rhinitis may alter NO ou tput and, therefore, the microbial colonization of the upper airways. Nasal surgery aimed at relieving nasal obstruction may do the same but would als o be expected to improve pulmonary function in patients with asthma and upp er airway obstruction. NO output rises in a number of conditions associated with chronic airway in flammation, but not all of them. Concentrations are increased in asthma, al lergic rhinitis, and viral respiratory infections, but reduced in sinusitis , cystic fibrosis, primary ciliary dysfunction, chronic cough, and after ex posure to tobacco and alcohol. Therefore, NO, similar to several other infl ammatory mediators, probably subserves different functions as local conditi ons dictate. At present, it seems that the measurement of NO in the upper a irway may prove valuable as a simple, noninvasive diagnostic marker of airw ay pathologies. The objective of this review is to highlight some aspects of the origin, ph ysiology, and functions of upper airway NO, and to discuss the particular m ethodological problems that result from the complex anatomy.