Lower respiratory infections: how infants differ from adults.

Largely for anatomic reasons, the peripheral airways of infants are more susceptible to inflammatory narrowing than are those of adults. When infection occurs in the lower respiratory tract of an infant, the primary effect is likely to be on the smaller airways, not the alveoli. The results are airtrapping and atelectasis. This airway obstruction often causes severe respiratory embarrassment. It is recognized on chest films by generalized hyperinflation and irregularity of aeration. Small airway obstruction is a common and important manifestation of lower respiratory infection in infancy. True consolidative pneumonia is much less frequent.