Rhinomanometry: do the anterior and posterior methods give equivalent results?

Nasal resistance to airflow was measured by both anterior and posterior rhinomanometry in 15 healthy volunteers. It was found that the posterior method gave values on average 16% higher than the anterior method. This difference was statistically significant. We propose that this is due to posterior rhinomanometry measuring the resistance of the nasopharynx as well as the resistance of the nose. In the past a discrepancy between the 2 methods has been claimed to be due to an error in the standard form of the parallel resistance equation. This hypothesis was tested by measuring total nasal resistance by posterior rhinomanometry and comparing this with a total nasal resistance value derived from posterior rhinomanometric measurements of the resistance of the individual nasal cavities. The standard form of the parallel resistance formula was used to derive the total nasal resistance. There was no significant difference between the 2 values for total nasal resistance. We conclude that if measurements are made at the same pressure gradient then the use of this equation is valid.