E. Baraldi et al., A simple flow-driven method for online measurement of exhaled NO starting at the age of 4 to 5 years, AM J R CRIT, 162(5), 2000, pp. 1828-1832
NO is increased in exhaled air of asthmatic patients, and may be used as a
marker of airway inflammation. The online method is a standardized techniqu
e for measuring exhaled nitric oxide (ENO). However, this method has proven
difficult for some children, who may have trouble maintaining a constant e
xpiratory flow. The aim of this study was to validate a modified technique
for online ENO measurement that utilizes a flow regulator to overcome the p
atient problem of having to actively maintain a constant expiratory flow. W
e measured ENO levers with two methods in 105 asthmatic and 10 healthy subj
ects, comparing the standardized (ST) single-breath method with a modified
single-breath, flow-driven (FD) method. With the ST method and visual monit
oring, the subjects inhaled NO-free air to TLC, and exhaled with a target f
low of 50 ml/s. With the FD method, the subjects exhaled from TLC and flow
was kept constant (50 ml/s) by the operator, using a flow regulator. The su
bjects were divided into two groups, one consisting of children aged 4 to 8
yr (n = 74) and the other of children aged 9 to 16 yr (n = 41). In the gro
up aged 4 to 8 yr, 38 children (51%) were unable to perform the ST method,
whereas only five children (7%) failed to perform the FD technique. In the
group aged 9 to 16 yr, only four children (10%) were unable to perform the
ST maneuver, and all successfully performed the FD maneuver. The mean conce
ntrations of ENO in the 73 children who performed both types of maneuver we
re similar (36.1 +/- 3.4 [mean +/- SEM] ppb with the ST method and 33.8 +/-
3.3 ppb with the FD technique, p = NS) and were highly correlated with one
another (r = 0.99, p < 0.0007). ENO values were significantly higher in st
eroid-naive than in steroid-treated asthmatic children. In conclusion, we d
escribe a modified online method for measuring ENO that is simple, does not
require active cooperation to maintain a constant expiratory flow, and can
be easily performed by children from 4 to 5 yr of age onward.