Journal of Applied Physiology, Vol 54, Issue 5 1236-1241, Copyright © 1983 by American Physiological Society
Dysanaptic lung growth: an experimental and allometric approach
J. P. Mortola
The postnatal development of the mammalian lung, which at birth has only a
fraction of the adult number of alveoli, would suggest a mismatch
(dysanapsis) of the changes in airway size and lung size with growth. This
may have implications on the efficiency of breathing because for any given
lung size the dimensions of the airways are the determinant of the amount
of dead space (VD) ventilation and of airflow resistance. A comparison of
the allometric functions of tracheal dimensions previously published
suggests that the tracheal volume, taken as representative of VD, is
smaller in newborns than in adults. This difference becomes more apparent
when examined per unit of functional residual capacity (VD/FRC). The
relatively smaller tracheal volume is the result of both a shorter and
narrower trachea in the newborn. This latter difference implies a slightly
but significantly higher resistance of the lower airways, as also
demonstrated by experimental measurements of peak expiratory flows at a
constant driving pressure in rats of different ages. Because the slightly
higher resistance of the lower airways is probably compensated by the
smaller resistance of the upper airways (J. Appl. Physiol.: Respirat.
Environ. Exercise Physiol. 51: 641-645, 1981), it would seem that the
structure of the newborn mammalian lung favors the alveolar ventilatory
function without a substantial increase of the energetic losses.
