Passive respiratory mechanics in healthy infants. Effects of growth, gender, and smoking
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J P Hanrahan1, R W Brown, V J Carey
1Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
Insights
Infant girls may have more mature breathing mechanics at birth. Maternal smoking during pregnancy negatively impacts infant respiratory compliance and resistance growth.
Area of Science:
- Pediatric Pulmonology
- Infant Respiratory Physiology
Background:
- Understanding normal respiratory mechanics in infants is crucial for identifying deviations.
- Factors like gender and maternal smoking can influence respiratory development.
Purpose of the Study:
- To characterize normal growth and variability in infant passive respiratory mechanics.
- To investigate the effects of gender and maternal smoking on these parameters.
Main Methods:
- Assessed passive respiratory mechanics in 127 healthy infants (2 weeks to 18 months) using the single-occlusion passive flow-volume technique.
- Measured respiratory compliance (Crs), respiratory resistance (Rrs), and passive respiratory time constant (Trs).
Main Results:
- Respiratory compliance (Crs) increased with infant length; respiratory resistance (Rrs) declined.
- Infant girls showed tendencies towards lower Crs at birth and slower growth compared to boys.
- Boys had higher Rrs at birth, but a faster decline in Rrs over time.
- Maternal smoking was linked to lower Rrs at birth and slower Crs/Rrs development.
Conclusions:
- Infant girls may possess more mature respiratory mechanics at birth.
- Postnatal respiratory maturation may proceed faster in infant boys.
- Maternal smoking during pregnancy adversely affects infant respiratory mechanics development.
Abstract:
This investigation characterizes the normal growth, variability, and effects of gender and smoking on passive respiratory mechanics in healthy infants. Passive respiratory mechanics were assessed at 193 test sessions on 127 infants (55 boys, 72 girls) between 2 wk and 18 mo of age using the single-occlusion passive flow-volume technique. Respiratory compliance (Crs) increased significantly with increasing infant length, whereas respiratory resistance (Rrs) declined. No significant gender differences were apparent for Crs, although there was a tendency for this measure to be both lower at birth and increase at a slower rate in girls than in boys. Rrs was significantly higher at birth in infant boys than in infant girls, but the rate of the normal decline in Rrs during the first 18 mo also occurred at a significantly greater rate in boys. The passive respiratory time constant (Trs) overall showed little change over this age range, but it was both lower near birth and increased at a significantly greater rate versus infant length in girls than in boys. Maternal smoking during pregnancy was associated with lower levels of Rrs at birth, as well as with significantly slower growth of Crs and natural decline of Rrs in the first 18 mo of life. These data suggest that infant girls may have more mature respiratory mechanics at birth, but that postnatal growth/maturation may be faster in boys.