Combination Therapy for the Treatment of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is characterized by repetitive collapse or 'obstruction' of the pharyngeal airway during sleep. These obstructions result in repetitive hypopneas/apneas and intermittent hypoxia/hypercapnia, as well as surges in sympathetic activity. Such processes disturb normal sleep and impair neurocognitive function, often resulting in excessive daytime sleepiness and decreased quality of life. Furthermore, OSA is associated with cardiovascular morbidity and mortality, making OSA a major health concern.

Current evidence suggests that OSA pathogenesis involves the interactions of at least four physiological traits comprising 1) the pharyngeal anatomy and its propensity towards collapse 2) the ability of the upper airway dilator muscles to activate and reopen the airway during sleep (i.e. neuromuscular compensation), 3) the arousal threshold from sleep (i.e. the propensity for hypopneas/apneas to lead to arousal and fragmented sleep) and 4) the stability of the ventilatory feedback loop (i.e. loop gain). Continuous positive airway pressure (CPAP) is the most common treatment for OSA but it is often poorly tolerated; only ~50% of patients diagnosed with OSA continue therapy beyond 3 months. Given this limitation, alternative approaches have been tested and have generally focused on the use of oral appliances, surgery, and more recently pharmacological agents.

However, these alternate therapies, when used alone as monotherapy, rarely abolish OSA completely. This is not that surprising given that these treatments focus primarily on correcting only one trait and ignore the fact that the pathogenesis of OSA is multi-factorial. Thus the investigators hypothesize that some patients could be treated without CPAP if more than one trait is targeted (i.e., the investigators take a multi-factorial treatment approach). Such a multi-factorial approach is not unusual in Medicine. Many disorders such as diabetes, asthma, hypertension, cancer and congestive heart failure are treated with more than one medication or modality. In our view, giving CPAP to all OSA patients is like treating every diabetic with insulin, or every asthmatic with oral steroids - these treatments, like CPAP, are poorly tolerated and ignore the complexity of the underlying biology.

The investigators recently published a technique that measures the four traits using repeated 'drops' in CPAP levels during sleep. Each trait is measured in a way that allows model-based predictions of the presence/absence of OSA. With this technique the investigators demonstrated in a small group of CPAP-treated OSA subjects that decreasing the sensitivity of the ventilatory feedback loop (i.e. reducing loop gain) by approximately 50% with either acetazolamide or oxygen reduces the apnea/hypopnea index (AHI) by half. Interestingly, our model allowed us to make the prediction that if, in addition to an agent that reduces loop gain, the investigators also gave a drug that increases the arousal threshold by at least 25%, then the investigators could potentially abolish OSA (rather than just reduce its severity by 50%). This is of great interest given that the investigators already have shown than eszopiclone increases the arousal threshold by approximately 30% and is associated with an improvement in the AHI. However, to date there has been no study examining the combination of an agent that reduces loop gain (i.e. oxygen) with one that increases the arousal threshold (i.e. eszopiclone) as a treatment for OSA.

To determine the effect of combination therapy on each of the four traits and how they contribute to our model prediction of OSA, as well as on apnea severity. Specifically the investigators will assess: