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The postnatal development and growth of the human lung. I. Morphometry
Insights
Human lung development occurs in two phases, with rapid growth of air and blood volumes in the first 18 months. This enhances oxygen transport and gas exchange efficiency as children grow.
Area of Science:
- Pediatric Pulmonology
- Developmental Biology
- Quantitative Anatomy
Background:
- Postnatal lung development is crucial for respiratory function.
- Understanding lung growth patterns informs the diagnosis and treatment of pediatric respiratory conditions.
Purpose of the Study:
- To investigate the morphometric changes in human lungs during postnatal development.
- To differentiate phases of lung growth and their impact on gas exchange.
Main Methods:
- Morphometric analysis of 7 children's lungs (26 days to 5 years) using light and electron microscopy.
- Comparison with previously published data from 8 adult lungs.
Main Results:
- Two distinct phases of lung development identified: 0-18 months (disproportionate air/blood volume growth) and 18 months-adulthood (proportionate growth).
- Airspace and capillary surface areas increased proportionally with lung volume throughout development.
- Pulmonary diffusing capacity for oxygen (DLO2) increased with body mass (exponent 1.15), driven by capillary blood volume expansion.
Conclusions:
- Human lung growth exhibits distinct phases impacting structural composition and gas exchange.
- Relative improvement in gas exchange efficiency per body mass is linked to capillary volume growth.
Abstract:
The lungs of 7 children (age: 26 days to 5 years 4 months) who died from non-respiratory causes were morphometrically investigated by means of light and electron microscopy. For analysis, the set of data was supplemented with results obtained previously on 8 normal adult lungs using similar quantitative techniques (Gehr et al., 1978). The results allowed us to distinguish two phases of postnatal lung development and growth, the first phase lasting from birth to about 18 months and the second phase from then to adulthood. The first phase was characterized by an overproportionate volume increase in the O2-transporting media, air and blood, at the expense of the parenchymal tissue compartment. In the second phase, the volumetric composition of the lung did not change further because there was proportionate growth of all lung compartments. The growth curves for the airspace and capillary surface areas were not biphasic: they increased in direct proportion to lung volume from birth to adulthood, indicating a steady increase in the air-blood interface complexity during the entire growth period. As a consequence of the differences in growth paces between the various structural lung components in early childhood, the morphometric parameters showed large variations in their overall growth rates between birth and adulthood. Thus, the parenchymal tissue components increased by a factor of 15, lung volume and the gas-exchange surface areas between 20 and 25 times (in parallel to body mass), and, finally, the O2-transporting media, air and blood, more than 30 times. The morphometrically determined pulmonary diffusing capacity for O2 (DLO2) scaled with body mass to the power of 1.15, a value significantly different from 1. This relative improvement with age of the gas exchange function per unit body mass is due mainly to an overproportionate growth of the capillary blood compartment.