Obstructive sleep apnea (OSA) is common in the aging population and is associated with increased risk of cardiovascular (CV) disease, including cerebrovascular injury. Repetitive exposure to acute CV response, such as sympathetic surge and blood pressure (BP) rise following obstructive respiratory events, is an important mediating mechanism linking OSA to CV disease and cerebrovascular injury. However, such acute CV responses are not effectively captured by conventional polysomnography metrics, such as the apnea hypopnea index (AHI) commonly used in OSA evaluation. This results in imprecise classification of patients in terms of their CV risk and may be responsible for inconsistent results in epidemiologic and clinical studies. More importantly, the uncertainty of the effectiveness of continuous positive airway pressure (CPAP) therapy in reducing the CV risk poses a significant challenge in therapeutic decision-making in older individuals. Therefore, the identification of additional phenotypic markers that better quantify the unfavorable CV effects of OSA and provide improved prediction of CV outcomes is crucial to improving risk stratification and clinical therapeutic decision-making. In this project, Barron Associates will investigate novel physiologic measurements that can readily be retrieved from a single photoplethysmography (PPG) sensor and investigate whether PPG features are associated with markers of subclinical, clinical CV disease, and cerebrovascular injury.