Establishing the feasibility of measuring bereavement-related stress in a naturalistic setting - PROJECT SUMMARY/ABSTRACT Spousal bereavement is associated with increased mortality, cardiovascular disease (CVD) morbidity, and diminished quality of life. While most individuals are resilient and eventually adjust to the loss, there is great variability in the type and severity of stressors that individuals experience in the first months following the loss. Grief self-report scales inquire about these stressors, but usually ask individuals to rate how often they experienced symptoms over the past 1-2 weeks. Although bereavement is a dynamic process, limited data is available on the day-to-day fluctuations in bereavement-related stress and the affective and physiological changes that follow. Affective stress reactivity refers to the changes in affect in response to a stressor while autonomic stress reactivity refers to changes in heart rate (HR) and heart rate variability (HRV). Both affective and autonomic stress reactivity have been associated with adverse mental and physical health outcomes in the general population. Emerging data also show that bereaved spouses have lower levels of HRV, indicative of a dysregulated stress response, when compared to married controls. Therefore, individual differences in stress reactivity among bereaved spouses may be linked to the detrimental health outcomes observed in this population. Our understanding of stress reactivity, however, comes from studies conducted in highly controlled laboratory settings and laboratory stressors are unlikely to capture the variety and severity of stressors experienced in bereavement. Thus, research examining stress reactivity among bereaved spouses in naturalistic settings is critically needed. The objective of the current study is to address this gap in the literature by establishing the feasibility of using stress reactivity to better capture experiences of daily stressors in spousal bereavement. We will use a novel approach that combines ecological momentary assessment with HRV measured by continuous electrocardiography (ECG) monitoring to generate personalized (person-level) measures of stress reactivity. Data will be used to develop two measures of stress reactivity: affective reactivity (changes in negative affect in response to a stressor) and autonomic reactivity (changes in heart rate and heart rate variability in response to a stressor). The pilot and feasibility data generated by this study will support future studies examining the role of stress reactivity as a mechanism linking bereavement, CVD, and other health outcomes.