Defence of the Lung

The neonatal defence mechanisms are immature. Intact cough reflexes are present in only 25% of preterm infants and sneeze is weak or absent in the early neonatal period.¹

Because of this, the immature mucociliary transport system is the only remaining mechanical barrier against inhaled or aspirated pathogens. It extends from the nasopharynx to the respiratory bronchioles. Pathogens are trapped and neutralized and then transported up the airway to be swallowed.

The mucociliary transport system consists of three layers;

Ciliated Epithelial Cells - each cell has many hair-like structures on its surface called cilia. The cilia beat entirely within the aqueous layer.

Aqueous Layer - a thin layer of low-viscosity fluid. The depth of this layer is critical for effective cilial movement.

Gel Layer - mucus floats on top of the aqueous layer. It traps pathogens and is moved from the airways by the cilia. The moisture content of the mucus is important as thick mucus is difficult to move.

Gas Conditioning and Heat and Moisture Recovery

References

1. Miller HC et al (1952) Variations in the gag, cough and swallow reflexes and tone of the vocal cords as determined by direct laryngoscopy in newborn infants. Yale J Biol Med 24;284