Abstract
Introduction: Tidal volume (VT) and respiratory compliance (Crs) are commonly normalised for body weight; whether this is appropriate beyond the neonatal period or in weight restricted children remains unclear.
Aim: To examine the relationship between VT, Crs and growth in healthy infants.
Methods: The Jaeger BabyBody (v4.6) was used to assess lung function (LF) in healthy, sedated term Caucasian infants.
Results: Technically satisfactory VT and Crs from 140 infants [median (range) age: 38 (3-105) w] were available on 192 & 84 occasions respectively (Table).
The average relationship between VT or Crs and weight was constant over time but between-subject variability increased with growth (Fig. 1a&b). 95% Limits based on VT/kg or Crs/kg would over-estimate predicted range in the youngest and under-estimate it in older infants, leading to potential misdiagnosis. VT/kg or Crs/kg were inversely related to weight z-score (Fig. 1c&d); light-for-age babies had higher values than those who were heavier. This again may lead to misdiagnosis especially in those with impaired growth (eg, CF).
Conclusions: Reporting infant LF/kg body weight is inappropriate. Equipment-specific regression equations are needed to avoid misinterpretation; for this a larger dataset is required. We would welcome contributions of similar data from other centres.
- © 2011 ERS