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.