[Evaluating oronasal flow with temperature (thermistor) and obstructive pressure (prongs)]

The measurement of oronasal flow during sleep studies using thermistors is internationally well accepted. As an alternative the possibility exists to measure the pressure at the nose by means of nasal prongs. Our objective was to compare and evaluate the methods to detect respiratory events in clinical routine, namely O2-saturation by pulse oxymetry oronasal flow by thermistors thoraco-abdominal effort by belts oronasal flow by prongs, 8 consecutive patients suspected of sleep apnoea syndrome (7 m, 1 f), mean age 56.5 +/- 9.5 years, height 173 +/- 6.4 cm, BMI 28.7 +/- 2.6 kg/m2, Epworth sleepiness scale score 9.1 +/- 3.2, AHI 24.9 +/- 13.7 h-1, lowest SaO2 86 +/- 4.9%, were examined. Between nose and mouth we fixed an oronasal 3-point thermistor and oronasal prongs (2 openings at the mouth and 2 openings at the mouth applying a common tube). During breathing the resulting pressure was registered with a pressure transducer parallel to the signal of the thermistors and the other polysomnographic data. We defined a respiratory event if at least one of the 4 signals met the criteria of a respiratory disturbance (for exact definitions see method). The detection rate of the 4 signals was calculated in relation to the sum of all events. Of the 1824 events (100%) only 52.3% were detected by an O2-desaturation of more than 4%, but 61.0% by thermistors. An acceptable detection rate was found measuring effort with 83.4%, only nasal prongs detected 95.1% of all events. We conclude that with regard to the detection rate of respiratory events the measurement of pressure by nasal prongs is superior to the use of thermistors.