[Regulative resistances during mouth breathing--a source of error determining nasal resistance by pulmonary function...

Methods to determine airway resistance - pulmonary function tests - have been recommended for the measurement of nasal resistance. Using the "oscillation method", you can demonstrate in some patients a source of error: Some mouth breathers can have an additional regulative resistance. By means of direct write-out tracings it is demonstrated that the simple subtraction of the resistances (during mouth and nose breathing respectively) is not a reliable method to determine nasal resistance. But the source of error can be recognized using a more luxurious measuring technique.