[Changes in the shape of choanal openings and airflow rates during development]

The shape of the choanal openings were examined in 173 babies aged zero to six months using digital video fiberscope inserted via nose. A numerical analysis and the fluid mechanics were then calculated for each recorded choanal opening. The choanal openings in one month old babies were a flat oval shape. Vertical development was faster than that of horizontal development, and the choanal openings changed from a flat oval to a round and finally a vertical oval shapes as the babies aged from two to four months. Both the air resistance and airflow ratio in the choanae can be calculated by Navier-Stoke's equation, if the choanae are assumed to be an oval tube. Using this equation, it was calculated that the air resistance ratio was one to five and the airflow ratio increased five times from neonates to six month old babies.