Single-breath exhaled nitric oxide in preschool children facilitated by a servo-controlled device maintaining constant flow.

Fractional concentration of exhaled nitric oxide (FENO), an index of airway inflammation, is optimally measured in adults and school-age children using a single-breath online (SBOL) exhalation at constant flow. However, preschool-aged (<6 years old) children have difficulty exhaling at constant flow, and alternative methods are needed. We employed a servo-controlled variable resistance device (servo device) that controls expiratory flow while allowing the child to vary expiratory pressure. To validate this device, 8 children (aged 6-12 years) performed SBOL exhalations with and without the servo device at expired flow rates between 20-50 ml/sec. We then studied 32 young children aged 24-71 months with the servo device alone at exhalation flows of 30, 40, and 50 ml/sec. Test difficulty (TD) with each method was rated by questioning the older children, or as observed by the physician obtaining the data in the younger children (0 = no difficulty, 1 = mild difficulty, 2 = moderate difficulty, and 3 = unable to perform test). In the older children, SBOL exhalations with and without the servo device demonstrated equivalent flow-dependence of FENO values. Test difficulty was low (0.125-0.625) at all flow rates, with excellent agreement between the two methods (P < 0.001). Twenty-eight young children (<6 years old) were able to complete measurements at all three flow rates evaluated. The 4 subjects who were not able to successfully complete all the measurements were between 2-3 years old (mean 2.75 +/- SD). Exhaled NO (mean +/- SD; ppb) was 8.8 (+/-6.2), 10.6 (+/-6.7), and 13.2 (+/-8.8) ppb at flows of 50 ml/sec, 40 ml/sec, and 30 ml/sec, respectively. Mean values of SD scores were 1.00, 1.14, and 1.43 at flows of 50, 40, and 30 ml/sec, respectively (P = NS). In conclusion, exhaled NO measurement by the SBOL method was facilitated in preschool children by the use of a servo-controlled variable resistance device. This device may allow these measurements to be applied to aid in the diagnosis and treatment of asthma in the preschool child, where spirometry is generally impossible. Copyright 2004 Wiley-Liss, Inc.