Measurement of tidal breathing flow-volume loops (TBFVL) is a frequently us
ed noninvasive method to investigate ventilation and pulmonary mechanics in
newborns. To investigate their intrasubject and intersubject variability s
hapes of averaged TBFVLs in 56 healthy newborns (group 1: median age and we
ight 7 days, 3100 g), 19 infants recovering from respiratory diseases after
neonatal care (group 2: 16 days, 2770 g), and 38 infants with bronchopulmo
nary dysplasia (BPD) (group 3: 80 days, 2465 g) were analyzed using the dea
d space free flow-through technique, which permits pneumotachographic long-
term measurements. We found a low intrasubject but a high intersubject vari
ability 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 hea
lthy 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 significa
nt (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, gru
nting) the high inter-subject variability of TBFVLs limits the diagnostic v
alue of a shape analysis during tidal breathing.