Changes in nasal cavity volume and target area of exposure to nasal drops with age in rats

The changes in the nasal cavity volume of rats with age and the area exposed to nasal drops administered into the nasal cavity were investigated. Results indicated that the nasal cavity volume lineally increased as rats grew older. In 7-week-old rats, the exposed area in the case of an administration volume of 25 microliters, based on practice, was naso-, maxillo-, and ethmoid turbinate and this volume was enough to expose the whole area of the nasal cavity including the ethmoid turbinate. On the other hand, in 27-week-old rats, administration volumes of 10 and 25 microliters were not enough to expose the ethmoid turbinate. This indicated that the exposed area tended to become narrower in 27-week-old rats than in 7-week-old rats, but the exposed area in the case of an administration volume of 50 microliters was naso-, maxillo-, and ethmoid turbinate in 27-week-old rats. In this case, the volume was enough to spread to the ethmoid turbinate. Differences in the exposed area might be caused by differences in the volume of the nasal cavity. It was also indicated that the main exposed area was the inferior meatus in the 30 min immediately after administration. At all administration volumes, however, notice should be taken of the outflow of nasal drops into the oral cavity through the nasopalatine.