Subglottic airway becomes stable with age in the human infant larynx.

Development of the mucosal defence system and its relationship to the pathogenesis of laryngeal diseases was studied by examining the changes in the laryngeal structures at the level of subglottic larynx of 59 human infants who died within 1 year of birth. By making a transverse section at the level of the cricoid cartilage, the area and diameter of each subglottic structure were examined using an image analysis system. The results were analysed, not only by their age at death, but also based on the total development score. The areas of the whole structure, cricoid ring, subglottic mucosa and inner cavity (available area) increased in close correlation with the total development score. In contrast to the increased diameter of the inner cavity, the thickness of the mucosa was almost the same size. These results indicate the stability of the subglottic airway with advancing age in the human infant larynx.