Assessment of upper airway mechanics during sleep
Section snippets
Obstructive sleep apnea
The obstructive sleep apnea hypopnea syndrome (OSAHS) is the most prevalent respiratory sleep disorder in both children (Lumeng and Chervin, 2008) and adults (Punjabi, 2008). It was recognized as a public health problem in the last decade (Phillipson, 1993). OSAHS is characterized by recurrent upper airway obstructions which can last up to ≈40 s each and occur up to ≈80 times per hour. These obstructions are caused by an abnormal increase during sleep in the collapsibility of the soft wall of
Modeling upper airway mechanics in obstructive sleep apnea
The mechanical properties of the upper airway and the obstructive events experienced during OSAHS can be interpreted by means of the Starling model of a collapsible conduit (Gold and Schwartz, 1996, Farré et al., 2003a). Fig. 2 presents the diagram of an experimental model mimicking upper airway mechanics during sleep (Farré et al., 1998). This analog model is based on a collapsible rubber tube, representing the upper airway wall, surrounded by a small chamber connected to a source of negative
Measurement of the critical pressure and upstream airway resistance during CPAP
The simple model in Fig. 2 captures the main features of upper airway mechanics (Fig. 5) and provides the rationale for non-invasively measuring Pcrit and Rup when a patient is subjected to CPAP (Gold and Schwartz, 1996). The method is based on the fact that Pcrit is the pressure for transition from a closed to an open upper airway and Rup is an index indicating how difficult it is to completely open the airway once it has been initially opened. In normal subjects, Pcrit is very negative (≈−15
Measurement of upper airway obstruction by forced oscillations during sleep
The forced oscillation technique (FOT) is a non-invasive method of measuring the mechanical impedance of the respiratory system during spontaneous breathing (Dubois et al., 1956, Pride, 1992). The technique is based on superimposing a small-amplitude high-frequency pressure oscillation to the patient's breathing and recording the pressure and flow oscillations. Given that the FOT frequency is higher than the frequencies generated by the respiratory muscles, the patient's respiratory impedance
Conclusions
The mechanical properties of the upper airway during sleep can be measured by means of two non-invasive methods. With one of them, the critical pressure and upstream resistance of the upper airway are determined by recording inspiratory flow at different nasal pressure values (for instance during a conventional CPAP titration procedure). This method to quantify upper airway mechanics has promising applications since the technology required (pressure transducer and pneumotachograph) is already
Acknowledgments
This work was supported in part by the Ministerio de Ciencia y Tecnología (SAF2005-00110 and SAF2004-00684).
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