Respiratory Development

child blowing out candlesRespiratory ailments are among the most common symptoms that cause parents to bring children to their doctor. Children are particularly vulnerable to respiratory conditions for a number of reasons involving features of their developmental stage, physical differences from adults and aspects of their behaviour.

Developmentally, a child’s respiratory anatomy is immature. The infant’s lungs are not fully developed at birth. Although bronchiolar branching is complete early in fetal life, alveolar development and cellular differentiation of lung tissue continues into adolescence. There is about a 23-fold increase in lung volume from birth (150-200 ml) to adulthood (5,000 ml) translating into a comparable increase in absorptive surface area.1

Although there are limited data studying this, there may be effects on respiratory development by exposure of fetal respiratory epithelium to contaminants that cross the placenta. It is known that "maternal smoking during pregnancy is associated with significant reductions in forced expiratory flow rates in the offspring. "2

There are also physical reasons that children are more vulnerable. Smaller lungs mean a relatively higher surface area to volume ratio, such that children are already absorbing a greater volume of contaminants relative to their body size compared to adults.

Also, a child’s breathing rate is faster than that of an adult, so every minute they exchange more air per kilogram of body weight. Older children in particular display the maximum air intake because of their greater activity levels.

Being smaller in size, a child’s breathing zone is much lower than that of an adult. Some heavier contaminants, such as pesticides or automobile exhausts, are typically present in a vertical gradient, being in higher concentration closer to the ground, therefore closer to the child’s breathing zone.

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