Forced oscillation technique for the evaluation of severe sleep apnoea hypopnoea syndrome: a pilot study

The forced oscillation technique (FOT) is a noninvasive method of potential clinical interest for quantitatively assessing airway mechanics during sleep, We investigated the applicability of FOT as a diagnostic tool for noninvasive assessment of airflow obstruction in patients with sleep apnoea/hypopnoea syndrome (SAHS) during sleep. In seven patients previously diagnosed with severe SAHS (mean+/-SD apnoea/ hypopnoea index (AHI) 67+/-14) we performed a full polysomnography (PSG) together with on-line measurement of respiratory impedance (\Z\) using FOT, For each patient me determined: 1) number of respiratory events conventionally detected by full PSG, those obtained by FOT and their degree of concordance; and 2) the characteristics and values of \Z\ during the respiratory events. FOT was well tolerated and easily applied in conjunction with a conventional sleep setup. The mean number of respiratory events.h(-1) detected by PSG and FOT were 55+/-16 and 58+/-17, respectively, with a strong Concordance, \Z\ increased from a baseline of 11+/-4 to 50+/-20 cmH(2)O . L-1. s during apnoea (mean+/-SD). In all but one patient intermittent increases of \Z\ occurred immediately before each obstructive apnoea, In four patients, the increases of \Z\ developed at end-expiration whereas in two others occurred during inspiration. During hypopnoea most of the patients showed decreases of \2\ during expiration, In conclusion, forced oscillation technique can be used as a noninvasive and complementary tool for the diagnosis of respiratory events and provides an on-line quantitative approach for continuous monitoring of airflow obstruction during sleep in patients with sleep apnoea/hypopnoea syndrome.