Variability of tidal breathing flow-volume loops in healthy and sick newborns

Measurement of tidal breathing flow-volume loops (TBFVL) is a frequently used noninvasive method to investigate ventilation and pulmonary mechanics in newborns. To investigate their intrasubject and intersubject variability shapes of averaged TBFVLs in 56 healthy newborns (group 1: median age and weight 7 days, 3100 g), 19 infants recovering from respiratory diseases after neonatal care (group 2: 16 days, 2770 g), and 38 infants with bronchopulmonary dysplasia (BPD) (group 3: 80 days, 2465 g) were analyzed using the dead space free flow-through technique, which permits pneumotachographic long-term measurements. We found a low intrasubject but a high intersubject variability of shapes in all groups. The incidence of normal TBFVLs was similar in all groups (group 1: 66%, group 2: 53%, group 3: 61%). The shape of the expiratory limbs in infants with BPD did not differ significantly from healthy newborns with exception of the incidence of linear or concave shapes (92 vs. 73%, p < 0.05). Nevertheless, the shape of the TBFVL has a significant (p < 0.001) influence on commonly used tidal breathing parameters which must be considered in the clinical interpretation. Unless the shape of the TBFVL illustrates certain respiratory behaviors (e.g., flow-limitation, grunting) the high inter-subject variability of TBFVLs limits the diagnostic value of a shape analysis during tidal breathing.