Accuracy of measurement and comparability of anterior rhinomanometry and whole body plethysmography in determination of nasal resistance. Studies with a mechanical model

The degree of accuracy of anterior rhinomanometry and the plethysmographic method in determining nasal resistance was examined in a mechanical model. The plethysmographic method allows a precise estimation of nasal resistance. It was found that the absolute variation of the plethysmographically measured values is not greater than 5%. Anterior rhinomanometry as described by Bachmann (2) allows a valid estimation of the pressure-flow relation. Here, too, inaccuracy remains within a range of 5% if the values are recorded with an X-Y-plotter. With the system developed by EVG, a microprocessor-controlled analysis is also possible. The flow rate is measured at pressure rates of 75, 150, and 300 Pa. Inconstancies in respiratory flow cause deviations from the correct pressure-flow graph. Should these deviations accidentally coincide with the predefined points of evaluation these erroneously achieved results will be assumed to be representative for the whole graph. This analytical fault has meanwhile been corrected by interpolating the points at the predefined pressure rates. Due to the differences in analytic techniques the methods of determining nasal resistance are not comparable in practice. The authors therefore recommend that, in addition to the usual results of analysis, average value of nasal resistance be determined for each measuring procedure. Today, this can be done without any problem by using microprocessors.