What you will learn
Body height can be used to empirically scale
lung volumes and
ventilatory flows.
However, this does not contribute to a fundamental understanding of
the laws that govern a successful growth pattern as it
does not take into account changing body dimensions during
growth.- Throughout the process of lung
growth the normal functioning of the organism as a whole
must be warranted. In the first years there is growth of
the number of alveoli and bronchi, and subsequently they
simply grow larger.
- As from age 6 year lungs and airways
appear to grow proportionally: isometric growth.
- The lung growth pattern in patients
with asthma is similarly isometric.
- Asthma patients, as well as individuals
who experienced recurrent respiratory symptoms during infancy,
exhibit a normal isometric growth pattern and yet appear
to have narrower airways.
- Due to the elastic properties
of lungs and chest,
the changes that occur with growth and aging,
and the changes that occur in the shape and properties
of the thorax,
neonates and elderly subjects have dependent lung areas
that are poorly or
nonventilated (airway closure) during
normal tidal breathing. On account of the shape of the
oxyhemoglobin dissociation curve the poorer oxygenation
of capillary blood in such lung compartments cannot be
compensated by increased ventilation elsewhere. This may
explain the lower arterial oxygen pressures observed in
these subjects.
Neonates, infants, toddlers and elderly subjects are therefore
at greater risk of more extensive airway closure in the
case of e.g.
viral infections, and thus to a compromised oxygen supply,
particularly when supine.
- Soon after birth the arterial
carbon dioxide tension attains adults values, which are
maintained to a very high age.
This indicates that the lung is up to its task of exchanging
gas across the alveolar-capillary membrane.