Thirty-seven male subjects referred to our sleep laboratory for suspected OSA syndrome after evaluation of spirometry to exclude subjects with bronchial obstruction were recruited for the study. Mean ± SD age was 46 ± 11 years, and mean body mass index (BMI) was 34 ± 7 kg/m2. None of the subjects had acute or known chronic cardiopulmonary or neuromuscular diseases. Each patient gave informed consent, and the study protocol was approved by the local scientific committee. All subjects underwent spirometry, nocturnal monitoring by a portable cardiorespiratory system, and NEP testing during tidal expiration.
Pulmonary function tests were performed during the day with the patient in a sitting position with a plethysmograph (Med Graphics Elite; Med Graphics Corporation; St. Paul, MN) according to the guidelines of the European Respiratory Society. Nocturnal monitoring was performed by a computerized system (Poly-MESAM; MAP; Martmsried, Germany). All recordings lasted > 6 h. V was detected by nasal cannulas connected to a pressure transducer (Pneumoflow; MAP). Apneas and hypopneas were visually scored. Apneas were defined as lack of flow for at least 10 s. Hypopneas were defined as discernible reductions in V or thoracoabdominal movements > 10 s followed by an arterial oxygen saturation fall > 3%. Apnea-hypopnea index (AHI) was calculated as number of apneas plus hypopneas per hour of estimated total sleep time. There are occasions when you do not have any opportunity to sleep because of sleep apnea but you should not bare it all – Canadian Neighbor Pharmacy www.webmolecules.com will assist you to select what is better in treatment of this disorder.
NEP was generated by a circular Venturi device (AeroMech Devices; Almonte, ON, Canada) attached to a tank of compressed air via an electrically operated solenoid valve. The solenoid valve had an opening time of 50 ms; it was automatically activated in early expiration and kept open for 2 s by software control (DirecWin version 2.18a; Raytech Instruments; Vancouver, BC, Canada). A pneumotachograph (model 3830; Hans Rudolph; Kansas City, MO) was connected to the mouthpiece. V and mouth pressure were also measured (DirecNEP model 200A; Raytech Instruments). The changes in V after application of NEP, inherent in our measuring set-up, were assessed by occluding the mouthpiece with a stopper and applying NEPs of -5 cm H2O and -10 cm H2O. As shown in Figure 1, after application of NEP, there was an initial spike in V that lasted approximately 20 ms and was followed by progressively decreasing oscillations that became very small after another 80 ms when V became constant. Similar results were obtained with NEP of – 10 cm H2O, except that the magnitude of the V spike increased. With NEP of – 5 cm H2O, the initial spike in V corresponded to approximately 0.3 L/s, while with NEP of – 10 cm H2O it amounted to approximately 0.4 L/s. In both instances, however, the initial V spikes were much smaller that those observed in our experimental subjects.
In all subjects, NEP tests at – 5 cm H2O and – 10 cm H2O in sitting and supine positions were performed in a random order during quiet breathing with a nose clip. NEP was readministered after breathing pattern stabilization. For this purpose, at least four regular breaths were allowed between two consecutive NEP applications. During the test, care was taken to keep the neck in a neutral position and the subjects awake. The V and mouth pressure signals were filtered through a low-pass filter and sampled at 200 Hz. Both digital signals were displayed in real-time on the computer screen and stored on computer for subsequent analysis. Data analysis was performed using software developed in our laboratory written in MATLAB 6.5 (The MathWorks; Natick, MA).
A new method was assessed in this study to evaluate upper airway obstruction, ie, extrathoracic EFL was measured as AV expressed as percentage of the peak V (%Vpeak) immediately after NEP application (Fig 2). The minimum V was identified in the first 200 ms of NEP application to avoid reflex and voluntary reactions to NEP stimulus. We also assessed EFL induced by NEP as V, in the flow-volume loop, during NEP application equal or inferior to the corresponding V in any part of the control flow-volume loop (EFL), expressed as percentage of control tidal volume (%Vt) [Fig 2] as previously performed. Values of EFL (%Vt) and AV (%Vpeak) were the average of four measurements.
Data are reported as mean ± SD and range. The values of AV (%Vpeak) and EFL (%Vt) were linearly correlated to AHI. Statistical analysis was performed by commercial software (Stat-View; Abacus Concepts; Berkeley, CA). A p < 0.05 was considered significant.
Figure 1. Comparison of flow signal behavior in a subject (upper trace) and in the experimental set-up with mouthpiece occluded by a stopper (lower trace) when applying NEP of- 5 cm H2O. Both signals have NEP application coincident.
Figure 2. Measurement of flow limitation on superimposed flow-volume curve during quiet breathing and during NEP by flow limitation evaluated (%Vpeak); and EFL measured as V, in the flow-volume loop, during NEP application, equal or inferior to the corresponding flow during control (EFL) expressed as %Vt.