Abstract
Background: Multiple breath washout (MBW) is used to measure peripheral ventilation inhomogeneity. ERS/ATS guidelines recommend calculating the lung clearance index (LCI) at 2.5% of tracer gas concentration, without clear recommendation for MR. Whether this arbitrary cut-off is best suited to detect lung disease in infants is unknown.
Aim: To compare LCI and MR results at different cut-off concentrations in infants with lung diseases.
Methods: We used sulphur-hexafluoride (SF6)-MBW measurements from 20 infants with cystic fibrosis (CF) and 18 preterm infants (PT) with different degrees of ventilation inhomogeneity and 20 healthy controls (HC) at the age of 4-6 weeks. We compared sensitivity of different end-concentrations between 5% and 1% for LCI and MR2 to detect pathological values above the upper limit of normal derived from HC.
Results: As known for LCI, MR results change significantly at different cut-off values. Mean MR2 in CF infants e.g. increases from 5.1 to 8.3 units between 5% and 1.5%.
In general, cut-offs between 4% and 2% showed the highest sensitivity to detect abnormal lung function. In CF, 21 out of 40 LCI and 20 out of 39 MR2 results were abnormal at 2.5% and 2%, respectively. In PT, 26 out of 36 LCI and MR2 measurements were abnormal at the 3% cut-off.
Conclusion: In contrast to FRC, both LCI and MR results depend dramatically on cut-off values. As the most sensitive cut-off in both patient groups lies around 2.5%, it does not seem to be necessary to wash out until 0%. Using the current recommendations, a large proportion of CF and PT infants shows abnormal values for LCI and MR2. Slight differences between disease groups need to be examined in larger samples.
- Copyright ©ERS 2015
