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

Ambient oxygen regulates epithelial metabolism and nitric oxide production in the human nose

The effects of ambient O(2) tension on epithelial metabolism and nitric oxide (NO) production (VNO) in the nasal airway were examined in nine healthy volunteers. Nasal VNO, O(2) consumption (VO(2)), and CO(2) production (VCO(2)) were measured during normoxia followed by gradual hypoxia from 21 to 0% O(2) concentration. Nasal VO(2), VCO(2), and respiratory quotient during normoxia were determined to be 1.19 +/- 0.04 ml/min, 1.60 +/- 0.04 ml/min, and 1.35 +/- 0.04, respectively. Hypoxia exposure to the nasal cavity significantly decreased both VCO(2) and VNO [VCO(2): 1.60 +/- 0.04 to 0.96 +/- 0.03 ml/min (P < 0.01), VNO: 530 +/- 15 to 336 +/- 9 nl/min (P < 0.01)]. VNO was reduced commensurately with gradual decline in O(2) tension, and the apparent K(m) value for O(2) was determined to be 23.0 microM. These results indicate that the nasal epithelial cells exchange O(2) and CO(2) with ambient air in the course of their metabolism and that nasal epithelial cells can synthesize NO by using ambient O(2) as a substrate. We conclude that air-borne O(2) diffuses into the epithelium where it may be utilized for either cell metabolism or NO synthesis.

Variations of nasal nitric oxide in a subject with allergic rhinitis: a longitudinal study

PURPOSE

Nitric oxide (NO) in the exhaled air is mainly produced by the upper respiratory airway mucosa, and the output of NO has been found to differ from normal in sinonasal disease. In allergic rhinitis (AR) nasal NO output (V(NO)) has been reported to increase compared with healthy individuals. The purpose of this study was to observe daily variations in V(NO) in a subject with AR and to investigate the effect of environmental factors on V(NO).

MATERIAL AND METHODS

We measured V(NO) daily in an individual with AR over a period of 5-1/2 months to determine the variability of V(NO) from day to day. We used a 41-year-old, nonsmoking volunteer with AR as our subject to investigate the relationship between V(NO) and some environmental factors likely to affect V(NO). The correlation between V(NO) and nasal symptom scores was also investigated. Daily ambient NO concentrations, humidity, atmospheric pressure, and atmospheric grass pollen concentrations were recorded along with morning nasal NO measurements. At each measurement session, online NO measurements were done from both nostrils at 5 L/min constant transnasal flow. During the study the subject had a short period of a cold and a short period of purulent rhinitis and started using a nasal steroid spray at the end of the study.

RESULTS

V(NO) levels for our subject were higher than previously published values for normal and allergic adults. There was an increase in V(NO) (the highest value throughout the study) in the prodromal period of the cold and a significant decrease (the lowest values throughout the study) during the cold. Change during the purulent rhinitis was less remarkable than change during the cold.

CONCLUSION

No correlations between environmental conditions (humidity, atmospheric pressure, pollen count) and V(NO) were found. V(NO) changes were also independent of specific and cumulative nasal symptom scores.

Upper airway neurogenic mechanisms

Stimulation of the nasal sensory nerves leads to sensations of pain and stuffiness. Type C nociceptive nerve releases neuropeptides including substance P and calcitonin gene related peptides that increase plasma extravasation and glandular secretion. This axonal response acts as an immediate protective mucosal defense mechanism. Recruited parasympathetic reflexes cause submucosal gland secretion via acetylcholine and muscarinic M(3) receptors. Itching, sneezing, and other avoidance behaviors rapidly clear the offending agents from the upper airways and protect the lower airways. Dysfunction of these nerves may contribute to allergic rhinitis, infectious rhinitis, nasal hyperresponsiveness, and possibly sinusitis. Sympathetic arterial vasoconstriction reduces mucosal blood flow, sinusoidal filling, and mucosal thickness, and so restores nasal patency. Loss of sympathetic tone may contribute to some chronic, nonallergic rhinopathies. Human axon responses differ from those in animals, an important distinction that limits extrapolation from other species.

A new method for the remote collection of nasal and exhaled nitric oxide

STUDY OBJECTIVES

The present study introduces a method that has been developed to improve the remote collection and transportation of gas samples from the nose and lungs.

DESIGN

Assessment of agreement between two methods of clinical measurements.

SETTING

Noninvasive exhaled gas measurement at a respiratory research laboratory.

PARTICIPANTS

Ten nonsmoking adult volunteers (median age, 44 years; age range, 33 to 53 years; men, 6; women, 4) were recruited.

MEASUREMENTS AND RESULTS

Exhaled nitric oxide (ENO) and nasal nitric oxide (NNO) outputs were measured directly (on-line) and remotely (off-line). With the velum closed, lung air was exhaled at fixed flows (ie, 6, 8, and 10 L/min) (ENO) or room-air was aspirated through the nose in series at one fixed flow (ie, 5 to 8 L/min) (NNO). The off-line nitric oxide (NO) measurements were achieved by a gas collection tube system, which consisted of a flow control unit, a tube reservoir with one-way valves at both ends, and an interrupter valve allowing the trapping of gas inside the tube and eliminating the inclusion of "dead space." After clamping, the reservoir may store and transport the gas samples for delayed analysis. The coefficient of variation of three consecutive NO measurements was < 3% for both on-line and off-line ENO and NNO. The correlations between on-line and off-line measurements in both ENO and NNO outputs were high (r = 0.99; R(2) = 0.99), and, unlike previous studies using bag-collection, the ENO outputs for on-line and off-line measurements were in good agreement (Bland-Altman test) at all flows tested.

CONCLUSIONS

The tube gas collection system eliminates the dead space and contamination during the gas sampling and permits the cost-effective and reliable off-line collection of both nasal and exhaled gas samples.