ACOUSTIC RHINOMETRY - AN EXPLANATION OF SOME COMMON ARTIFACTS ASSOCIATED WITH NASAL DECONGESTION

The nasal cavities of 51 healthy volunteers were examined using acoust ic rhinometry before and after nasal decongestant. Several specific di mensions were studied, which included the minim um cross-sectional are a, and three volumes corresponding to the anterior, middle and posteri or regions of the nasal airway. An average acoustic rhinometry trace w as constructed for the whole group of subjects. before and after decon gestion, from data extracted from the raw data files written to the co mputer hard disk for each subject. A 27.5% (P < 0.0001) increase in th e minimum cross-sectional area was observed, with no shift in its posi tion. The greatest increase in nasal dimensions was seen in the anteri or and middle parts of the nose, however, significant changes were als o seen in the posterior nasal cavity and post nasal space. There are a number of possible sources of artefact. First, confusion of the first and second minima may produce apparent movement of the minimum cross- sectional area following nasal decongestion. Second, a postulated chan ge in the acoustic path length may lead to apparent changes in volume in certain regions of the nest. Third, a variable and uncontrollable d egree of sound energy loss will occur into the opposite nasal cavity b eyond the posterior border of the septum. An apparent increase ill the dimensions of this region will be seen as the opposite cavity deconge sts. We feel that all users of the acoustic rhinometer need to be awar e of these potential sources of artefact, and attention needs to be fo cused on an agreed definition of the components of the acoustic rhinom etry trace.