Passive respiratory mechanics measured during natural sleep in healthy term neonates and infants up to 8 weeks of life

The single occlusion technique (SOT) is a simple and noninvasive technique for measurement of passive respiratory mechanics in infants. Reference values based on measurements of a large population of healthy infants performed outside specialized research laboratories are lacking. The aim of this study was to present reference values for passive respiratory mechanics based on a large population of healthy term neonates and infants measured during natural sleep in routine care. As part of the ongoing Wheezing Illnesses Study Leidsche Rijn (WHISTLER), the compliance (C-rs) and resistance (R-rs) of the respiratory system were measured in 450 healthy unsedated neonates and infants with a mean age of 4.6 +/- 1.3 weeks. Multivariable regression analysis, with gestational age, age at measurement, body size, sex, and ethnicity as possible predictors, was carried out to estimate prediction equations for mean C-rs and R-rs values. Technically acceptable lung function measurements could be performed in 328 (73%) neonates and infants. Median C-rs was 39.5 (range 14.8-79.1) ml/kPa and median R-rs was 7.4 (range 3.8-19.5) kPa/L/sec. The following regression equations for C-rs and R-rs were obtained: In C-rs = 1. 677 + 1.3 x 10(-4) xbirth weight (g)+0.030 x birth length (cm) and In R-rs=2.496-3.1X10(-6) x birth length(3) (cm(3))-0.114 x sex. We provided reference values for passive respiratory mechanics using the SOT in a large population of healthy term neonates and infants measured during natural sleep. These data provide a frame of reference for assessing the normality of SOT measurements performed in routine care.