Clinical Application of the Forced Oscillation Technique for CPAP Titration in the Sleep Apnea/Hypopnea Syndrome

Abstract

We have previously demonstrated that upper airway obstruction in sleep apnea/hypopnea syndrome (SAHS) can be accurately assessed in real-time by measuring respiratory impedance (|Z|) with the forced oscillation technique (FOT). The aims of the present study were: (1) to determine the feasibility of identifying the optimal continuous positive airway pressure (CPAP) for patients with SAHS based on analysis of the |Z| signal during conventional polysomnographic CPAP titration studies; and (2) to evaluate practical issues involved in the application of FOT during CPAP titration. We performed CPAP titration in 28 patients with SAHS during polysomnography (PSG) (14 nap and 14 full overnight studies) using a FOT system applied continuously to obtain an on-line measurement of |Z|. FOT was easily implemented and was well-tolerated by the patients. Optimal CPAP levels were determined both in the conventional manner from the standard PSG titration record and during a separate blinded analysis using the FOT signal alone. The mean conventional versus FOT-based optimal CPAP values were similar for both nap studies (10.6 +/- 0.6 [mean +/- SEM] versus 11.1 +/- 0.6 cm H(2)O, respectively, p = 0. 054) and overnight studies (9.9 +/- 0.7 versus 9.9 +/- 0.6 cm H(2)O, respectively, p = 1.00). Subsequent analysis of the PSG record with the FOT signal incorporated demonstrated that artefacts in the |Z| tracing occurred during mask leak, mouth breathing, and movement during arousal. Such abnormalities were readily identified from the flow tracing. These results indicate that, for adequate interpretation, the tracing and values of respiratory impedance obtained by FOT should be evaluated in conjunction with the flow signal. Continuous FOT-guided CPAP titration is feasible and may be a useful adjunct during manual titration. FOT could also potentially serve as the basis for automated CPAP in SAHS.

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.…”

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.…”

“…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].…”

“…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].…”