Relationship of lung recoil to lung volume and maximum expiratory flow in normal children.

Thirty-one normal children, aged 6--18 yr, were studied by measurements of static lung volumes, static expiratory pressure-volume (PV) curves, and maximum expiratory flow-volume (MEFV) curves. A theoretical standard volume was used to compare children of differing size and this showed that total lung capacity (TLC) is also a valid standard volume. The shape of the PV curve was found to change so that static elastic recoil at a fixed proportion of TLC was higher in older than in younger children. This was also true of static recoil at functional residual capacity (FRC) and an associated increase in the ratio of FRC to TLC was interpreted as evidence for increase in outward recoil of the chest wall during childhood. Since static recoil at "closing capacity" (CC) remained constant, a decrease in the ratio of CC to TLC was quantitatively explained by the PV shift during childhood. Although maximum expiratory flow at various lung volumes increased in constant proportion to TLC, "upstream conductance" decreased relative to TLC. It was concluded that maturation of the respiratory system is disproportionate in several features during childhood and that these disproportions are likely to be even more prominent during infancy and early childhood.