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

Abstract

Patients with obstructive sleep apnoea/hypopnoea syndrome (SAHS) experience repeated episodes of increased upper airway resistance leading to profound disturbances in sleep architecture and arterial blood gases [1,2]. Repeated inspiratory efforts occur during an obstructive sleep apnoea until arousal ensues and airway patency is restored [3]. The increased upper airway resistance in patients with SAHS can be assessed indirectly by the analysis of different signals, such as the time profile of the inspiratory flow signal, the noise of snoring, the use of strain gauges or inductance plethysmographs [4][5][6][7]. However, as the recent description of the upper airway resistance syndrome has pointed out [8], the classical noninvasive techniques previously described are unable to detect the full range of respiratory-related flow events that occur throughout the night. A more direct quantitative approach is the recording of the inspiratory driving pressure by means of an oesophageal catheter [8][9][10], although this has limited applicability in routine studies. Accordingly, methods to quantify changes in airway resistance noninvasively are required.The forced oscillation technique (FOT) provides a noninvasive method to quantify and assess the degree of airway obstruction, thus avoiding the need for a measurement of oesophageal pressure. It consists of superimposing on spontaneous breathing a small pressure oscillation through a nasal mask attached to the patient [11]. Respiratory impedance (| Z |) is derived from pressure and flow signals recorded at the nasal mask. Because patient co-operation is not required the technique can be applied during sleep. The potential applicability of FOT to assess airway obstruction in SAHS studies has recently been substantiated in a model study [12]. | Z | measured by FOT was found to be an accurate index of overall airflow obstruction [12]. The aim of the present study was to ascertain whether FOT is applicable in human diagnostic sleep studies for noninvasive assessment of airway obstruction in SAHS patients. Specifically, we were interested in testing whether respiratory events detected by FOT corresponded with those recognized by more conventional approaches. Furthermore, we wished to establish whether the FOT could be an adequate method continuous monitoring of airway mechanics dur- 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 | Z | 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 appro...

Forced oscillation measurements do not affect upper airway muscle tone or sleep in clinical studies

“…Frequency analysis of the EEG signal was carried out and no evidence of neurological activation was found. These findings are consistent with the clinical experience with FOT [3][4][5]. Significant effects on the upper airway or the EEG produced by the use of FOT, with and without CPAP, were not observed in subjects with SAHS.…”

“…13 The forced oscillation technique (FOT) is a simple and noninvasive method that allows continuous online monitoring of airflow obstruction during sleep, even in the absence of flow, as occurs in apnoeas. FOT has been applied in clinical diagnostic studies in patients with sleep apnoea/hypopnoea syndrome (SAHS) [1][2][3][4] and in continuous positive airway pressure (CPAP) titration studies [5,6] with highly encouraging results.…”

Forced Oscillation Technique in the Detection of Smoking-Induced Respiratory Changes

“…Multi-frequency is preferred in studies exploring the patterns or mechanisms of the frequency dependence of Zrs in health and disease. In contrast, single-frequency is used in the study of relatively rapid changes in Zrs, such as the changes observed during the respiratory cycle (Dellacà et al, 2004), deglutition apnea (Souza et al, 2008), deep inspiration (Slats et al 2007), and the evaluation of airway patency in sleep apnea (Badia et al, 1998;Lemes et al, 2003). A characteristic feature of COPD is that Zrs is often very different between inspiration and expiration, in contrast to the situation in normal subjects (Dellaca et al, 2007;Bates et al, 2011).…”

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

“…Previous studies in patients with OSA have indicated that major upper airway narrowing or collapse can be reliably identified when the impedance value increases to levels more than twice baseline values during tidal breathing [16,27]. Therefore, for the various categories of respiratory events we determined the proportion of events for which |Z| exceeded this value.…”