Technical abilities and limitations of acoustic rhinometry optimised for infants.

The objective of this model study was to validate in detail the technical capabilities as well as the limitations of a new rhinometric probe optimised for infants in order to improve reliability of measurements and reduce the risk of misleading conclusions. The repeatability was excellent (CV < 0.6%) and the reproducibility was high (CV% < 4%) provided the ambient conditions were fairly stable. The repeatability declined when external noise levels were above 60 dB SPL, and variation in temperature and pressure reduce reproducibility. The accuracy of the minimum cross-sectional area (MCA) as well as the volume corresponding to the nasal cavity in infants (VOL4), was acceptable (% error < 12%) as long as the MCA was larger than 30-40% of the probe dimensions and the cross-sectional area of the cavity posterior to the MCA did not exceed the MCA by a factor of more than 3-4. Variation in the position of the MCA within the anterior 2 cm has minimal influence on the posterior measurements provided the shape and length of the MCA are unaltered. Rods inserted into the tubular model to simulate the slit-like shape of the nasal passage did not reduce the accuracy, which is essential to the clinical value of acoustic rhinometry. Recommendations and guidelines designed to enhance the reliability of acoustic measurements in infants are presented.