Aerodynamic influences on nasal nitric oxide output measurements

Nitric oxide (NO) concentration in aspirated nasal air is flow-dependent. N asal NO outputs calculated from steady-stale plateaux at flows <1 l/min are substantially smaller than those at flows >2 l/min. This study aimed to de termine the differences in NO output as calculated from the NO concentratio n plateaux in aspirated nasal air, resulting from different aspiration flow s. Nasal NO was determined by chemiluminescent analysis of air obtained fro m the nasal passages in series during velopharyngeal closure in 8 healthy a dults (flows: 0.2-3.7 l/min) and 5 with symptomatic allergic rhinitis (flow s: 0.2-3.7 l/min). Mean NO output in the healthy subjects was stable at app roximately 315 nl/l/min at flows of 0.2-0.7 l/min, and increased to a secon d steady output level of approximately 400 nl/l/min (+28%, p < 0.0001) at m ore physiological flow rates of 2.7 l/min and higher. The symptomatic subje cts had substantially higher NO output at all flows (p < 0.001) (709.3 nl/m in at 3.7 l/min) than the non-allergic subjects. The flow dependency of the nasal NO output may be explained by failure at low flows for the air strea m to penetrate the peripheral parts of the complex nasal passages, and by t he presence of a laminar flow regime in which a marginal lamina would tend to insulate the main stream from the mucosa. Thus, previously reported NO o utputs obtained at low flows may underestimate nasal NO output compared to output at higher and more physiological transnasal airflow rates, thus affe cting interpretation of results.