Acoustic rhinometry is one of standard diagnostic tools in objective evaluation of nasal patency. It provides information on the geometry of nasal cavities by using acoustic waves (sound) generated by the device. Acoustic rhinometry can detect narrow points within the nose that may lead to nasal blockage. Acoustic rhinometry does not provide information on nasal respiratory function and does not measure breathing, like rhinomanometry. The acoustic rhinometer generates an acoustic wave which is transmitted through a tube into one nostril. The size and the pattern of the reflected sound waves provide information on the structure and dimensions of the nasal cavity, with the time delay of reflections correlating with the distance from the nostril. The conversion of echo measurements to nasal volume requires mathematical calculations and theoretical assumptions, which is done by the computer connected to the recording device. In a congested nose, or in the nose with nasal polyps or tumor, the narrowest points are located deeper in nasal cavity, and acoustic rhinometry can detect the position of this point, however, cannot differentiate what is the blocking factor.
It is an easy and non-painful procedure to perform. The patient sits in upright position, clears its' nose and places the nosepiece into the nostril. Room where acoustic rhinometry is performed should be standardized in terms of temperature and humidity. Silence during measurement is essential. The nosepiece should fit the nostril, ensuring an airtight seal. Measurements are performed during breath holding.
When the measurements are performed before and after the application of a nasal decongestant spray, the differences in cross-sectional diameter of the nose can be attributed to nasal mucosal congestion. Data obtained after nasal decongestion allow the evaluation of anatomical factors influencing the cross-sectional diameter of the nose.
Acoustic rhinometry can be used also to check the impact of long-term medical treatment on nasal blockage due to rhinitis, rhinosinusitis or nasal polyps. It can measure the volume of nasal cavities helping in objective evaluation of nasal polyp size reduction after medical treatment. Specific challenge tests based on the application of allergen onto the nasal mucosa in the allergic patient may show extent of congestion by showing reduced nasal volume. However, it should be stated that acoustic rhinometry, as well as rhinomanometry data on nasal patency do not correlate well with patients’ subjective perception on nasal blockage.