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Exhaled nitric oxide can be detected in exhaled air and is readily measured by chemiluminescence. It is thought to be involved in both the regulation of ciliary motility and host defence. Recently, upper airway NO has been found to be reduced in a small number of children with primary ciliary dyskinesia (PCD) and its measurement has been recommended as a diagnostic test for this condition. The aim of this study was to compare the levels of NO in the upper and lower airways in a larger number of children with proven PCD with those found in healthy children. Exhaled NO was measured in the upper airway by direct nasal sampling during a breath-hold and in the lower airway as the end-tidal plateau level, using a chemiluminescence NO analyser. Upper airway NO levels were significantly lower in PCD (n = 21) than in the healthy children (n = 60) (mean +/-SD, 97+/-193, 664+/-298 parts per billion (ppb), respectively, p<0.0001). In PCD, the lower airway NO levels were also reduced (2.17+/-1.18, 5.94+/-3.49 ppb, respectively, p<0.0001). The levels were not associated with steroid use and did not correlate with lung function. Although there was some overlap between normal children and those with primary ciliary dyskinesia with regard to lower airway NO, nasal NO discriminated between the two groups in all but one child in each group. Measurement of nasal NO therefore may be a useful screening test for primary ciliary dyskinesia.
Karadağ et al. (Tue,) studied this question.