Greater nasal nitric oxide output during inhalation: effects on air temperature and water content.

The nose conditions the temperature and humidity of nasal air, and the nasal mucosal vasculature supplies heat and water for these processes. We hypothesize that nitric oxide (NO) modulates these processes through vasoactive effects on nasal mucosal vasculature. We measured the temperature, humidity and NO concentrations of nasal air during inhalation and exhalation across the nose and calculated net heat, water and NO output before (controls, n=7) and after inhibition of NO synthase by topical l-NAME (N=5) in healthy humans. We found that calculated NO output across the nasal passages is approximately three-fold greater during inhalation (503+/-105 nL/min) compared with exhalation (162+/-56 nL/min). Moreover, topical administration of l-NAME decreased nasal air temperature and humidity conditioning and NO output, but these effects were limited to inhalation. We conclude that nasal NO output is greater during inhalation than exhalation in humans. Our findings also support a role of nasal NO in temperature and humidity conditioning of nasal air.