PASSIVE RESPIRATORY MECHANICS IN HEALTHY INFANTS - EFFECTS OF GROWTH,GENDER, AND SMOKING

This investigation characterizes the normal growth, variability, and e ffects of gender and smoking on passive respiratory mechanics in healt hy infants. Passive respiratory mechanics were assessed at 193 test se ssions on 127 infants (55 boys, 72 girls) between 2 wk and 18 mo of ag e using the single-occlusion passive flow-volume technique. Respirator y compliance (Crs) increased significantly with increasing infant leng th, whereas respiratory resistance (Rrs) declined. No significant gend er differences were apparent for Crs, although there was a tendency fo r this measure to be both lower at birth and increase at a slower. rat e in girls than in boys. Rrs was significantly higher at birth in infa nt boys than in infant girls, but the rate of the normal decline in Rr s during the first 18 mo also occurred ata significantly greater rate in boys. The passive respiratory time constant (Trs) overall showed li ttle change over this age range, but it was both lower near birth and increased at a significantly greater rate versus infant length in girl s than in boys. Maternal smoking during pregnancy was associated with lower levels of Rrs at birth, as well as with significantly slower gro wth of Crs and natural decline of Rrs in the first 18 mo of life. Thes e data suggest that infant girls may have more mature respiratory mech anics at birth, but that postnatal growth/maturation may be faster in boys.