Determination of Upper Airway Collapsibility During Routine CPAP Titration

OSA is defined by total or partial intermittent collapse of the upper airway, resulting in nocturnal hypoxemia and arousals from sleep. OSA is incredible common and has important cardiovascular (e.g. hypertension, coronary artery disease, stroke, atrial fibrillation) and neurocognitive consequences (e.g. depression, motor vehicle accidents). Thus, OSA results in significant morbidity and mortality and a substantial economic burden. The best studied treatment of OSA is continuous positive airway pressure (CPAP), which effectively stents the upper airway open, however, many patients are not able to tolerate it. Other treatments are available, such as oral appliances or upper airway surgery, however these are much more variable in their effectiveness.

Although other factors are important, the most important factor in OSA pathogenesis is upper airway collapsibility. The upper airway collapsibility can be determined during sleep when patients with OSA are on CPAP. The CPAP level is decreased until flow limitation and finally collapse is achieved. The pressure at which the airway collapses is called the pharyngeal critical closing pressure, or Pcrit. When measured in research laboratories, the Pcrit correlates with OSA severity. Subjects with a high Pcrit (e.g. 5cm of water pressure) typically have severe OSA, while those with a lower Pcrit (e.g. 2cm of water pressure) have mild OSA, and those with a negative Pcrit (e.g. -4cm of water, the airway must be sucked closed to collapse) typically have no disease. The Pcrit may also have important implications for treatment. For example, patients with OSA and a very high Pcrit may require CPAP, however, those with a lower or slightly negative Pcrit might be successfully treated by an oral appliance. Thus, knowledge of the Pcrit might be useful in clinical practice, but it is rarely measured outside of the research lab.

To measure Pcrit, patients sleep with a mask over their nose or nose and mouth, and CPAP is applied using a custom made machine that can rapidly change mask pressures. The idea is that rapid changes in airway pressure produce a clear step change in airflow that will be observed quickly. In contrast, during clinical titrations, the CPAP machines change pressure much more slowly to help promote patient comfort. The goal of this research is to determine whether these slower pressure changes could still be used to gather useful information about upper airway collapsibility.