Über den Einfluss verschiedener nasaler Staudruckaufnehmer in der schlafmedizinischen Diagnostik

Nasal pressure as an indirect measurement of airflow is a well-established method to assess respiratory disorders. The AASM Manual 2007 defines criteria for data analysis of nasal pressure recordings applied in the diagnostics of OSAHS. Nasal prongs represent an essential part of the required instrumentation. Despite large differences in terms of size and shape of nasal cannula, there are no guidelines concerning the applicability of the various models. Therefore the aim of this study is to investigate the possible influence of different, commonly used nasal cannulas on pressure recordings. The measurements are conducted in a laboratory setting in order to generate constant and reproducible measuring conditions. We use a sine wave pump for flow generation that is connected to a flexible tube system ending in two nostrils of an artificial silicone head. This silicone head is required to attach the nasal prongs of the pressure transducer. Simultaneously, we measure the flow with a pneumotachygraph to receive the gold standard reference signal. In a second series we vary the diameter of the nostrils and in a third the pump volume to evaluate a possible influence of these parameters on the nasal pressure recording. Our results show that the various prongs exhibit significantly different absolute pressure amplitudes. However, repeated measurements with the same nasal cannula also yield ambiguous amplitude values. We explain this observation by the dependence of the signal amplitude on the nasal prongs position in the nostrils. This laboratory result supports hints in previously conducted patient studies. By contrast, the normalized signals of the different nasal prongs show a high level of agreement. This result implies that the shape of the pressure curves of the different nasal prongs is highly similar. Thus a certain flow decrease leads to a corresponding relative nasal pressure drop which is almost identical for all tested prongs. In clinical practice, relative reduction of nasal pressure is used to identify respiratory events. According to our findings the choice of the nasal prongs has no significant influence on the diagnosis of respiratory events by nasal pressure recordings. Further test series presented in this work provide evidence that this result is independent of the nostril cross section and is moreover not affected by the pump volume or flow amplitude.