Evaluating the usefulness of automatic continuous positive airway pressure (CPAP) in treating the sleep apnea-hypopnea syndrome (SAHS) is not easy because the algorithms for automatic CPAP implemented in the devices available are not well known and are probably dependent on the device. In addition, at present it is not possible to test the behavior of automatic CPAP devices in response to well-defined breathing patterns. Our aim was to implement a bench test to characterize the responses of automatic CPAP devices by subjecting them to breathing patterns of patients with SAHS. To this end, a variety of typical breathing patterns (normal, apneas, hypopneas, flow limitation, snoring) previously recorded in patients with SAHS during sleep were reproduced by a breathing waveform generator. Five commercially available automatic CPAP devices were tested. The responses of the devices to apneas, hypopneas, flow limitation, and snoring were considerably different. In some devices, the response was modified by air leaks similar to the ones found in patients. Consequently, the effectiveness of automatic CPAP assessed in clinical tests performed by using particular devices has no general validity. Testing automatic CPAP devices in a bench study is a useful first step in evaluating the performance of this new type of device in adjusting nasal pressure for each patient.

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Respiratory disturbances in patients with the sleep apnea-hypopnea syndrome (SAHS) may be detected by means of nasal prongs (NP) pressure (PNP). Nevertheless, PNP is nonlinearly related to flow (V). Our aim was to demonstrate the relevance of linearizing P NP for assessing hypopneas and flow limitation in SAHS. V was measured with a pneumotachograph during the hypopneas and flow limitation events in a continuous positive airway pressure (CPAP) titration in six patients with severe SAHS. These flow patterns were reproduced by a flow generator through an analog of the nares and recorded by NP. PNP was linearized [V NP = (PNP)1/2] by a specially designed analog circuit. For each event we used V, P NP, and V NP to compute the hypopnea flow amplitude (HFA) and a flow limitation index (FLI). Owing to NP nonlinearity, PNP considerably misestimated HFA and FLI. By contrast, V NP provided HFA and FLI values that were very close to those obtained from V: HFA (V NP) = 1.098. HFA(V) - 0.063 (r2 = 0.98) and FLI(V NP) = 1.044. FLI(V) + 0.004 (r2 = 0.99). Square-root linearization of NP greatly increases the accuracy of quantifying hypopneas and flow limitation. This procedure, which could be readily carried out in routine practice by means of the analog circuit we developed, is of interest in optimizing the assessment of respiratory sleep disturbances in SAHS.

The increase in the prevalence of chronic respiratory diseases has resulted in a rise in health services provided at home. The forced oscillation technique (FOT) proves to be a useful tool when it is desired to assess lung function noninvasively, and particularly for patients in whom spirometry cannot be applied. As no portable FOT device is currently available, the aim of this study was to design and test a portable FOT system for ambulatory and home care applications.The system devised is based on a microprocessor, which allows online computation of respiratory resistance (Rrs) and reactance (Xrs) and reliability indices. The portable device was compared with a conventional FOT system by using signals from 14 patients with chronic respiratory disease.This device has the same computation capabilities and flexibility as conventional FOT systems and meets the requirements for home application. Rrs (14. This portable forced oscillation technique device could be a useful tool for monitoring respiratory mechanics in ambulatory and home care applications.

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...

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As active patient cooperation is not required, the forced oscillation technique (FOT) could be suitable for measuring airway obstruction in routine home applications. Nevertheless, FOT has never been used at the patient9s home to date. The aim of this study was to assess the feasibility of FOT and the reproducibility of measured respiratory resistance (Rrs) in routine patient self-testing at home.Altogether, nine asthmatic patients self-measured their Rrs with a portable FOT device and spirometry for 10-14 days, in the morning and evening, and before and after bronchodilator inhalation. During each measurement session, the patients carried out four consecutive FOT measurements. Grubbs9 discordancy test for detecting outliers was used to evaluate intermeasure reliability.Only 4.9% of Rrs data reported by patients were rejected as artefacts. The coefficient of variation of Rrs was 7.9¡6.3% (mean¡SD). When compared with spirometry, the per cent change in Rrs for detecting a positive bronchodilator response showed an 83% sensitivity and 72% specificity.Unsupervised self-measurement of respiratory resistance at the patient9s home provided results similar to those obtained by a technician in a lung function lab. Forced oscillation technique could be a useful tool for the routine follow-up of asthmatic patients at home. Eur Respir J 2003; 22: 668-671.

Increased upper airway collapsibility in the sleep apnea/hypopnea syndrome (SAHS) is usually interpreted by a collapsible resistor model characterized by a critical pressure (Pcrit) and an upstream resistance (Rup). To investigate the role played by the upstream segment of the upper airway, we tested the hypothesis that breathing different gases would modify Rup but not Pcrit. The study was performed on 10 patients with severe SAHS (apnea-hypopnea index: 59 +/- 14 events/hour) when breathing air and helium-oxygen (He-O2) during non-REM sleep. The continuous positive airway pressure that normalized flow (CPAPopt) was measured. Rup and Pcrit were determined from the linear relationship between maximal inspiratory flow VImax and nasal pressure (PN):VImax = (PN - Pcrit)/Rup. Changing the breathing gas selectively modified the severity of dynamic (CPAPopt, Rup) and static (Pcrit) obstructions. CPAPopt was significantly (p = 0.0013) lower when breathing He-O2 (8.44 +/- 1.66 cm H2O; mean +/- SD) than air (10.18 +/- 2.34 cm H2O). Rup was markedly lower (p = 0.0001) when breathing He-O2 (9.21 +/- 3.93 cm H2O x s/L) than air (15.92 +/- 6.27 cm H2O x s/L). Pcrit was similar (p = 0.039) when breathing He-O2 (4.89 +/- 2.37 cm H2O) and air (4.19 +/- 2.93 cm H2O). The data demonstrate the role played by the upstream segment of the upper airway and suggest that different mechanisms determine static (Pcrit) and dynamic (Rup) upper airway obstructions in SAHS.