Nitric oxide production in PCD: Possible evidence for differential nitric oxide synthase function

Primary cilliary dyskinesia (PCD) is characterized by decreased levels of fractional exhaled nitric oxide (FeNO), thought to reflect low activity of airway inducible nitric oxide synthase (iNOS) levels. Alveolar NO (C-alv) concentration and bronchial NO (J(NO)) flux can be calculated from FeNO measured at multiple exhalation flow rates. We hypothesised that whereas bronchial NO would be reduced in PCD due to reduced iNOS function, alveolar NO would reflect endothelial NOS (eNOS) function and be normal. We recorded the medical history; measured FeNO at multiple flow rates (50, 100, 200, 260 ml/sec); and performed spirometry in 24 children (aged 8-16 years). FeNO50 of the PCD children was significantly lower than normal mean (+/- SD) 8.1 +/- 1.3 ppb versus 12.5 +/- 1.6 ppb, P= 0.033. The mean SD values of PCD (n = 24) and normal (n = 20) subjects were respectively: JNO: 383.5 +/- 307.9 versus 650.1 +/- 489 pl/s, P= 0.033, Calv: 1.60 +/- 0.78 versus 1.60 +/- 0.75 ppb, P= NS. We show that C-alv is normal in PCD, demonstrating that there is no generalized disorder of NO handling in this condition. This differs from a previous report. Furthermore, we speculate that these data may provide supportive evidence that variable flow NO measurements can assess the relative activity of iNOS and eNOS.