Daily ambulatory exhaled nitric oxide measurements in asthma

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Abstract
Exhaled NO (FENO) is a non‐invasive, validated marker for asthmatic airway inflammation. Recently, a new hand‐held NO‐analyzer has been developed which makes it possible to monitor FENO at home. We assessed feasibility and analyzed variability of daily FENO home measurements. Twenty‐one asthmatics (mean age 14.5 yr; range 8–25 yr) participated. Nineteen used a stable dose of inhaled corticosteroids and all of them were in a stable clinical condition. FENO was measured twice daily for 14 consecutive days. Measurements and symptom scores were recorded on a smart card in the analyzer. Symptom score items included well‐being, wheeze, activity, and nocturnal symptoms. Measurements showed a success rate of 93%. We found a significant diurnal variation in FENO with geometric mean morning levels 14% higher than evening levels (95% CI: 4%–25%; p = 0.013). Individual subjects showed marked fluctuation of FENO. The mean intrasubject coefficient of variation of FENO was 40% for morning and 36% for evening values. FENO and cumulative symptom scores did not correlate. Home FENO measurements are feasible, and offer the possibility to asses airway inflammation on a daily basis. Further study is needed to interpret and evaluate possible benefits of FENO home monitoring.