Physiological significance of exhaled nitric oxide during exercise

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While the exhaled gas passes through upper airway and nasal cavity, i t acquires nitric oxide (NO) in these sites. The final origin of NO in the airway is not clear, but it seems that NO may diffuse out of the airway epithelia to the lumens. In order to estimate the outflux of NO in the airway, we have measured the exhaled NO from the nasal cavity and mouth separately. For this purpose we have developed a real-time measurement system for exhaled NO.This device can automatically measure both NO concentration and VNO.VNO,of which unit is nl/min, is a production rate for exhaled NO.This parameter is the only useful tool to estimate the amount of NO from the airway.1. Nasal NOWe studied human nasal NO in healthy volunteers. The subject was asked to perform a voluntary closure of soft palate (VCSP) in order to ventilate nasal airway from the right (or left) nostril to the left (or right). The VNO of the nose was measured approximately 300 nl/min. After 4 min of moderate exercise, the VNO wa … More s significantly decreased by 30%. The close measurement of NO in the nose with an inserted tube revealed that the nasal NO has pattern of oscillation which synchronized with that of pulsatile changes of nasal mucosal blood flow. These results suggest that the nasal NO is arising from epithelia and/or vascular bed of nasal mucosa.2. NO from lower airwayThe real-time measurement clarified many unknown aspects of exhaled NO.The pattern of single breath of exhaled NO (VNO) is always peaked at the early period of expiration (0.1 to 0.3 sec after beginning of expiration) and tapered abruptly in the end-expiratory period. This suggests that NO in the lower airway may originate in the sites close to the alveolus, probably periphery to terminal bronchioles. The breath hold can increase VNO simply depending on the breath hold time. The linear relationship between VNO and the time strongly suggests that NO is continuously sprung from the airway wall at constant rate. Another interesting finding was that alveolar ventilation is correlated with VNO.This suggests that NO is picked up by the alveolar gas while it is passing by. In conclusion, NO production in the airway is stable and continuous during resting and measurable in a unit of VNO. Less