Sleep Apnea Endophenotypes: One Size Does Not Fit All

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Project Summary OSA is defined by repetitive collapse of the upper airway, a process which leads to transient hypoxemia and arousals from sleep, and is associated with various cardiovascular, metabolic, and neurocognitive consequences. OSA is the most common respiratory disorder, affecting roughly 10% of middle aged men and women in the USA and up to 1 billion globally. Although continuous positive airway pressure (PAP) is an efficacious therapy, it is not always well tolerated and adherence is less than ideal. OSA is increasingly recognized as a multifactorial disorder that can occur in different people for different reasons, not only due to anatomical predisposition (collapsibility of the upper airway), but also related to low arousal threshold (wake up too easily), dysfunction in upper airway dilator muscles and instability in ventilatory control. Through careful measurement of these underlying factors and the symptoms experienced in OSA, this proposal seeks to understand how different mechanisms underlying OSA – endotypes – lead to different symptoms or consequences – phenotypes. These different phenotypes range from having no appreciable symptoms, to falling asleep at the wheel, to experiencing cardiometabolic consequences. Additionally, addressing the underlying cause might be useful to personalize therapy, to predict adherence to PAP, and to understand which symptoms will or will not improve with long term PAP therapy. A major challenge in clinical practice is understanding whether particular symptoms are due to OSA, and whether these symptoms will improve with treatment. Moreover, we are currently struggling to find alternative therapies for OSA which will likely depend on underlying mechanism. Similarly, we do not currently know which patients to put into clinical trials since it seems unlikely that, e.g., all OSA patients will have cardiovascular benefits to PAP therapy since not all are at risk of heart disease. Our goals are 1) To understand the contribution of the underlying cause, or endotype, of OSA to the symptoms experienced by people with OSA, 2) To elucidate how the endotype predicts response to non CPAP therapies, such as oxygen or sedative hypnotics, and 3) To define how underlying endotype (mechanism) mediates changes in phenotype (clinical manifestations of disease) with treatment of OSA. Ultimately we hope that our efforts will advance the OSA field and help to alleviate suffering or reduce/prevent disease burden.