The stress, salt excretion, and nighttime blood pressure (SABRE) study: Rationale and study design

Background: Abnormal diurnal patterns of blood pressure (BP) on ambulatory BP monitoring (ABPM), defined by reduced BP dipping or elevated nighttime BP, are associated with increased risk for adverse cardiovascular events. Psychological stress is associated with abnormal diurnal patterns of BP. Exposure to an acute stressor (e.g., mental stress task) normally increases urinary sodium excretion. However, some individuals have sodium retention after stress provocation, revealing substantial between-person variability in the degree of stress-induced sodium excretion. Prior research suggests urinary sodium excretion that does not occur during the daytime may shift toward the nighttime, accompanied by an increase in nighttime BP. Associations between psychological stress and the diurnal patterns of sodium excretion and BP are not yet fully understood. Design: The study is conducted in both the laboratory and naturalistic environment with a multi-racial/ethnic sample of 211 healthy adults. In the laboratory, change in urinary sodium excretion in response to mental stress tasks is examined with pre-/post-stress assessments of sodium excretion. Changes in angiotensin-II, catecholamines, BP, heart rate, endothelin-1, and cortisol are also assessed. In the 24-hour naturalistic environment, the diurnal patterns of sodium excretion and systolic BP are assessed as daytime-to-nighttime ratio of sodium excretion and ABPM, respectively. Ecological momentary assessments of perceived stress are also collected. Summary: The SABRE study investigates previously unexplored associations between stress-induced urinary excretion in the laboratory, diurnal patterns of sodium excretion and BP in the naturalistic environment, and ecological stress. It has high potential to advance our understanding of the role of psychological stress in hypertension.