Static compliance of the respiratory system in healthy infants

We recorded static deflation pressure-volume (PV) curves from near TLC to FRC in 49 healthy, sedated, spontaneously breathing infants of 1 to 104 wk of age. Respiratory activity was transiently inhibited by inflating the respiratory system several times to a volume at an airway pressure of 30 cm H2O (V-30) Passive deflation from V-30 to FRC was then interrupted by multiple brief occlusions at the airway opening, in order to measure static recoil pressures. The expired volume from V-30 to FRC was defined as V-30E. Compliance of the respiratory system (Crs) was calculated as the slope of the linear portion of the PV curve from 5 to 15 cm H2O. Crs and V-30E increased with increasing body length (p < 0.001). After adjustment for body length, males had greater Crs values than did females (p < 0.01). V-30E was smaller in female infants (p < 0.05) and in infants whose mothers smoked during pregnancy (p < 0.04). Specific compliance (Crs/V-30E) declined with increasing age (p < 0.01), but there were no differences related to sex or maternal smoking. We conclude that static deflation PV curves can be recorded in the age range from 1 to 104 wk, and that maternal smoking may produce hypoplastic lungs.