Assessment of upper airway mechanics during sleep

https://doi.org/10.1016/j.resp.2008.06.017Get rights and content

Abstract

Obstructive sleep apnea, which is the most prevalent sleep breathing disorder, is characterized by recurrent episodes of upper airway collapse and reopening. However, the mechanical properties of the upper airway are not directly measured in routine polysomnography because only qualitative sensors (thermistors for flow and thoraco-abdominal bands for pressure) are used. This review focuses on two techniques that quantify upper airway obstruction during sleep. A Starling model of collapsible conduit allows us to interpret the mechanics of the upper airway by means of two parameters: the critical pressure (Pcrit) and the upstream resistance (Rup). A simple technique to measure Pcrit and Rup involves the application of different levels of continuous positive airway pressure (CPAP) during sleep. The forced oscillation technique is another non-invasive procedure for quantifying upper airway impedance during the breathing cycle in sleep studies. The latest developments in these two methods allow them to be easily applied on a routine basis in order to more fully characterize upper airway mechanics in patients with sleep breathing disorders.

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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