Forced oscillation technique: a help for screening patients with sleep apnoea syndrome and severe obesity?

Objectives: Aim of our study was to asses pulmonary function and whether are differences in sitting, orthostatic and supine position, to evaluated airways resistances and impedances by forced oscillations technique (FOT), in healthy, obese snoring and obese with sleep apnea syndrome (SAS) subjects.Materials and methods: We evaluated 41 obese patients (BMI 38.13 ± 6.9 Kg/m2, 22 males and 19 females, age between 15 year old 79 year old), by a complete polysomnography (Pseries Compumedics Sydney) to distinguish 14 simple snoring (AHI < 5/h) from 27 SAS (AHI < 20/h) patients. All the patients underwent also common blood samples, ABG, chest X-ray, ECG, spirometry and FOT method (IOS Jaeger), a non-invasive and effort-independent test, to measure the respiratory system mechanical impedance, in the standard sitting position, then in the orthostatic and in supine ones (with the bed set on the 180°). 14 healthy, non-obese, non-snoring, non-SAS subjects formed the control group. Results: See Table 1. Oscillation frequency: ________________________________________ 5 Hz ________________________________________ 20 Hz ________________________________________ Healthy Snoring SAS Healthy Snoring SAS Sitting/supine R 12% 24% 36% 9% 21% 27% Sitting/supine X −14% −31% −26% −4% −28% −147% Standing/supine R 27% 25% 46% 19% 22% 34% Standing/supine X −21% −29% −50% −5% −51% −123% R = resistance, X = reactance. Conclusion: Spirometry in standard sitting position is not able to evaluated patients’ respiratory pattern during the sleep. On the contrary, spirometry + FOT, which measures respiratory system mechanical impedance, when performed in the sitting, orthostatic and supine position, has a higher sensitivity than a spirometry in recognizing SAS patients, both for screening, and to predict their nocturnal respiratory pattern.