Evaluation of a simplified oscillation technique for assessing airway obstruction in sleep apnoea

Abstract

The forced oscillation technique (FOT) is a noninvasive method that is useful for assessing airway obstruction and for titrating continuous positive airway pressure (CPAP) in patients with sleep apnoea. The aim was to evaluate the routine applicability of a simpli®ed FOT set-up based on recording pressure and¯ow at the level of the CPAP device, i.e. obviating the need for connecting the transducers to the nasal mask.A correction to account for the tubing and the exhaust port was applied. This simpli®ed FOT was evaluated on nine patients with moderate or severe sleep apnoea during routine CPAP titration. Patient impedance measured by the simpli®ed FOT (|Z|) was compared with actual patient impedance (|Zrs|) measured simultaneously with a reference FOT based on recording pressure and¯ow at the nasal mask.An The sleep apnoea/hypopnoea syndrome (SAHS) is characterized by recurrent elevation of air¯ow obstruction due to total or partial collapse in the upper airway. The forced oscillation technique (FOT) is a noninvasive method particularly suitable for assessing airway impedance during application of nasal continuous positive airway pressure (CPAP) [1] and, in particular, during the apnoeas and hypopnoeas in patients with SAHS during sleep [2,3]. Recent studies have demonstrated that FOT may be a helpful tool for the diagnosis of SAHS [4] and for the titration of the level of CPAP to treat the patient [5±7].Widespread routine application of this technique in the clinical arena would be facilitated by simplifying the conventional FOT set-up used in previous studies. One possible simpli®cation of the method, which could improve patient comfort and clinical applicability, consists in recording pressure and¯ow at the inlet of the tubing connecting the CPAP device and the nasal mask. This procedure would avoid the connection of the pneumotachograph and pressure transducers to the nasal mask, which is the conventional setting [1±6]. With such a simpli®ed FOT the impedance actually measured would not be actual patient impedance but the combination of patient impedance with the impedances of the tubing and the effective impedance of the nonlinear exhaust port. Nevertheless, airway obstruction could be adequately estimated by correcting the measured impedance for the artefacts induced by the tubing and the exhaust port, as recently shown in a calibration study on mechanical analogues [8]. The aim of the present work was to determine whether this simpli®ed FOT approach is easily applicable and reliable for measuring airway obstruction in routine sleep studies. To this end, the simpli®ed FOT was evaluated when routinely applied in nine patients with SAHS during sleep. The results obtained with this simpli®ed FOT approach were compared with those simultaneously obtained with a reference FOT setting based on recording pressure and¯ow at the nasal mask. Methods PatientsThe study was carried out on nine patients with a diagnosis of moderate or severe SAHS documented by polysomnography. The patients had not been previousl...

Evaluation of upper airway patency during Cheyne–Stokes breathing in heart failure patients

“…The FOT-derived impedance |Z| signal has previously been used to identify upper airway obstruction during sleep in OSA [17]. Upper airway closure is a dynamic process in OSA associated with an instantaneous large increase in respiratory resistance, which cannot be accounted for by other changes within the respiratory system.…”

“…Oscillatory impedance measured using the FOT FOT was applied as previously described [17,18,25]. A fullface mask was connected to a mesh wire-based pneumotachograph (resistance50.522 L?s ) through all the tubing was applied to the system in order to avoid rebreathing.…”

“…FOT systems have been developed which measure impedance (|Z| cmH 2 O?s?L -1 ) of the respiratory system during sleep in a continuous fashion without disturbing sleep architecture or altering upper airway muscle tone [19]. FOT has been shown to be a sensitive indicator of dynamic changes in upper airway calibre during obstructive events [17] and can be used to detect respiratory events and guide CPAP titration [16,20,21].…”

“…The forced oscillation technique (FOT) is a noninvasive method for instantaneous measurement of respiratory system mechanics which has been shown to be reliable in assessing upper airway calibre during sleep in patients with obstructive sleep apnoea (OSA) [16][17][18]. FOT systems have been developed which measure impedance (|Z| cmH 2 O?s?L -1 ) of the respiratory system during sleep in a continuous fashion without disturbing sleep architecture or altering upper airway muscle tone [19].…”

Noninvasive detection of expiratory flow limitation in COPD patients during nasal CPAP

“…In the present study, only one false-negative misclassification out of the 372 analysed breaths was found, suggesting that leakages may have negligible effects on the detection of EFL by FOT. Moreover, as the pneumotachograph can easily measure leakages [20], the presence of abnormally large leaks can be automatically identified, to indicate the possible loss of reliability in detecting EFL.…”