Short-term and seasonal variations of exhaled and nasal NO in healthy subjects

Summary

Nitric oxide (NO) is an important biological mediator with a variety of cellular and tissue functions. Fractional exhaled (FE_NO) and nasal NO (FN_NO) are known to be altered in several respiratory tract disease and disorders. However, there are rather few studies into the reproducibility of FE_NO or FN_NO measurements in healthy subjects.

The aim of this study was to examine both short- and long-term variations of FE_NO and FN_NO. In addition to intraday, day-to-day and week-to-week variations, the seasonal variation was assessed.

The data revealed that FE_NO and FN_NO levels were lower in the mornings compared to the afternoon values. There were clinically significant correlations in day-to-day (morning values 121.4±37.5 vs. 119.8±29.6, $r=0.868$, $P=0.000$), week-to-week (morning values 121.4±37.5 vs. 128.0±32.1, $r=0.637$, $P=0.000$) and seasonal (winter 133.5±29.7, summer 138.1±47.6, autumn 121.4±37.5, $r=0.624$, $P=0.000$) values of FN_NO. Day-to-day (morning values 14.6±6.7 vs. 14.2±5.1, $r=0.784$, $P=0.000$) week-to-week (morning values 14.6±6.7 vs. 15.4±7.3, $r=0.738$, $P=0.000$) and seasonal (autumn 14.6±7.2, winter 16.6±6.4, summer 17.4±8.0, $r=0.709$, $P=0.000$) levels of FE_NO were also highly reproducible.

Serial FE_NO and FN_NO measurements can be used in the monitoring of respiratory tract inflammation. Due to the diurnal variation of FE_NO and FN_NO, in long-term follow-up the measurements should be performed at the same time of day.