Therefore, measuring exhaled nitric oxide may be useful in assessing airway inflammation and monitoring the effectiveness and compliance of inhaled steroid medication in the asthmatic patient. The exciting news is that measuring ENO is not difficult since breath sampling is noninvasive and practical. Most of the studies done to date measure nitric oxide using a chemiluminescence analyzer which detects the photochemical reaction between NO and the ozone in the analyzer. The beauty of this method is the ability to measure ENO directly in line to the analyzer or indirectly by obtaining an exhaled air sample in a balloon to be later analyzed at a more convenient time. To date reported values for ENO have varied widely most likely due to significant differences in sampling technique.
Major differences relate to exhalation flow rate and nasal contamination.
For the past year we have focused our research on determining the most effective method for analyzing and collecting ENO samples in the pediatric population. In our studies subjects inhale scrubbed room air quickly to total lung capacity. Nasal contamination is eliminated by having the subject exhale against a fixed resistance while maintaining a constant expiratory pressure that is displayed on a computer screen. Maintaining a fixed expiratory pressure ensures vellum closure preventing nasal NO contamination and provides a fixed controllable exhalation rate. We have verified that ENO plateau levels increase as flow rate decreases.