[Measurement of expired nitric oxide concentration]

Much interest has been focused on standardization of measurement of expired nitric oxide (NO) concentration. The aim of this study was establish a simple measurement of expired NO concentration.

This study included 5 healthy male adults. To clarify whether NO is excreted in expired air constantly, its concentrations were measured while changing the flow rate. To examine the influence of NO derived from the nasal cavity, we compared expired No concentrations sampled from the month with those sampled from the endotracheal tube inserted to the trachea at a constant flow rate serially.

Expired NO concentrations decreased in inverse with the flow rate. No may be serially excreted in expired air. When serial changes of expired No concentrations sampled from the mouth were examined, its NO concentration initially reached a peak, then showed a plateau. Serial changes of those sampled from the endotracheal tube showed only a plateau. Plateau levels were not different between the two kinds. Therefore the peak values may have been influenced by NO derived from the nose that fell in the trachea by inspiration. Plateau values appeared to represent airway and lung-derived NO.

A simple measurement of expired NO concentration should be sampled from the mouth at a constant flow rate serially. Evaluating plateau values is appropriate for expired NO concentration.