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

Abstract

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.

Fig. 1

Measurements of nasal nitric output (nL/min) during inhalation (left panel) and exhalation (right panel) are shown in a cartoon depicting the nasal passages. Arrows indicate direction of airflow. NO concentration was measured at the inlet to the nasal passages (nasal sill) or in the posterior oropharynx during slow, steady-flow vital capacity inhalation and exhalation maneuvers in seven adult humans. Thoracic volume changes over time were used as a measure of the airflow rates during inhalation or exhalation. NO output (the product of NO concentration and airflow rate) was calculated at both the nasal sill and in the posterior oropharynx and used to determine the directional net change in NO output during inhalation and exhalation (black box values). There was a roughly three-fold greater net output of NO during inhalation compared with exhalation during the vital capacity maneuvers. *p < 0.008 vs. exhalation.

Fig. 2

Measurements of nasal NO concentrations (left panel) and airflow rates (right panel) in seven adult humans performing slow vital capacity maneuvers. These values were used to calculate the NO output values shown in Fig. 1. During inhalation and exhalation slow vital capacity maneuvers, the NO concentration was greater in the direction of airflow indicating addition of NO to the nasal air stream. *p < 0.002 vs. nasal sill values. However, the NO concentrations at the nasal sill during slow vital capacity exhalation were less than the NO concentrations measured in the posterior oropharynx during inhalation. **p < 0.02 vs. inhalation NO concentration in the posterior oropharynx. Since the airflow rates were not different in the various maneuvers (right panel), increased NO output during inhalation shown in Fig. 1 is due to an increased concentration of NO released into the nasal air stream during inhalation.

Fig. 3

Measurements of nasal NO output during inhalation (left panels) and exhalation (right panels) following topical application of an aerosol of saline (upper panels) or L-NAME (lower panels) in five adult subjects. Arrows indicate direction of airflow. Values post saline are similar to those of Fig. 1 and indicate that the vehicle control for L-NAME had no significant effect on nasal NO output. Post L-NAME, NO output was reduced (p < 0.02) during inhalation compared with post saline values, but exhalation values were not significantly different. Post L-NAME, inhalation NO output was greater ((p < 0.02) than NO output during exhalation. *p < 0.008 vs. post saline exhalation. **p < 0.02 vs. post L-NAME exhalation and vs. post saline inhalation.