[Comparison of anterior rhinomanometry and impulse oscillometry in nasal provocation with histamine]

Anterior rhinomanometry (aR) is the standard method for measurement of nasal resistance, but it has some drawbacks because it requires full co-operation of the patient and the results are disturbed by forced ventilation due to stenosis. The patient must generate flow by active ventilation. Resistance results from the flow/pressure ratio. Forced oscillation technique (IOS) does not affect spontaneous breathing. Flow/pressure ratio is generated externally by a loudspeaker. IOS measures not only resistance but also reactance. Whereas former methods used only a single frequency IOS is capable of applying and analysing frequencies between 0 and 100 Hz. The range from 5 to 35 Hz is useful for diagnostic issues. We compared IOS with aR in nasal provocation tests with histamine and checked the sensitivity of resistance (R) and reactance (X) at different frequencies.

20 patients (13 m, 7 f) underwent nasal challenge test using increasing doses of histamine (max. 3.2 mg). Resistance (aR, IOS) and reactance (IOS) were measured parallel. To compare the two methods, we calculated the dose of histamine which is required to double nasal resistance.

1. IOS demonstrates the increase of R at all frequencies. 2. The highest increase of R is measured at a frequency of 5 Hz (5 Hz: NaCl 0.41 +/- 0.25; Hist. 1.26 +/- 0.57; 35 Hz: NaCl 0.36 +/- 0.172; Hist. 0.60 +/- 0.1 kPa/l/s, p < 0.001). 3. The critical dose is significantly lower in IOS than in aR (2.29 +/- 2.59 vs. 1.06 +/- 1.16 mg/ml, p < 0.02). 4. Basal values of R do not differ significantly between aR and IOS (0.37 +/- 0.12 vs. 0.41 +/- 0.25 kPa/l/s, p < 0.001).

We conclude from our results that IOS is at least equivalent to aR in measuring nasal resistance. R at 5 Hz is the most important parameter in IOS. IOS is less dependent on the cooperation of the patient. In case of stenosis it does not require forced ventilation to achieve the required flow-pressure ratio.