[Comparative study of thoracic and abdominal effort, respiratory oscillatory impedance (ROI) and intrathoracic pressure in sleep apnea syndrome].

Oesophageal pressure (Pes) and oronasal flow are necessary to describe upper airway obstruction in patients with obstructive sleep apnoea syndrome (OSAS), but Pes interferes with sleep. We developed a device applying an oscillating flow (20 Hz) through a nasal mask. An additional flow (2.6 l/min) is needed to reduce dead space and humidity. 24 patients (age 55.8 +/- 8.3 years, BMI 28.6 +/- 3.9, RDI 38.6 +/- 19.4, Raw 0.27 +/- 0.07 kPa/s/l) underwent polygraphy (oronasal flow, thoracic and abdominal effort, oxygen saturation, microphone, heart rate). Pes and oscillatory impedance (OI) were measured simultaneously. During snoring, hypopnoeas and apnoeas we compared Pes, OI and effort values for the detection of number and period of airway obstruction. The average Pes during habitual snoring was -3.2 +/- 0.8, during hypopnoeas -3.9 +/- 1.1 and during apnoeas -4.4 +/- 1.6 kPa. We found no significant difference in respect of the number and period of obstruction in patients with apnoeas, whereas in patients with incomplete obstruction (hypopnoea) Pes and OI were found to be more sensitive in detecting obstruction than effort (period: 27.0 +/- 9.1 sec (Pes), 29.0 +/- 4.8 sec (OI) vs. 20.0 +/- 6.8 sec (effort); number: 34.0 +/- 9.1 (Pes), 35.0 +/- 8.5 (OI) vs. 23.0 +/- 9.5 (effort). There is a significant correlation between Pes and OI (r = 0.89). OI is shown to be equally sensitive in identifying Upper Airway Resistance Syndrome as compared to Pes. This method is more convenient than conventional measurements such as Pes and it could be an alternative.