SUMMARY OF WORK. A recent study in our laboratory confirmed that regular practice of a device-guided slow breathing exercise (DGB) decreased resting blood pressure (BP) in hypertensive patients, and that those changes were accompanied by decreases in breathing rate and increases in tidal volume at rest. However, this study failed to document that 24-hr blood pressure level was decreased by the breathing exercises. Other findings of changes in heart rate variability and no changes in 24-hr urinary excretion of marinobufagenin were consistent with the conclusion that the sympathetic nervous system influence on blood pressure was diminished by regular practice of the breathing exercise. In addition, we have analyzed changes in vascular structure and function that mediate the effects of regular device-guided slow breathing exercises on resting blood pressure in patients with pre-hypertension and mild hypertension. Analyses of hour to hour variability in 24-hr systolic and diastolic blood pressure were made before and after four-week breathing interventions in patients who daily practiced either the slow-breathing exercise or a spontaneous-breathing control exercise. These analyses revealed that variability in 24-hr systolic blood pressure was greater in older than younger subjects, and that variability of systolic blood pressure was decreased after the slow-breathing intervention, but not after the control intervention. The interpretation of these findings is limited by the fact that systolic blood pressure variability is dependent on age and blood pressure level. In addition, however, it was also found that the ratio of systolic to diastolic blood pressure variability decreased significantly after the slow-breathing intervention, but not after the control intervention. This latter measure, the Blood Pressure Variability Ratio (BPVR), has been found to be independent of age and blood pressure level, and to be a risk factor for cardiovascular mortality (reviewed by Schillaci G &Parati G, J. Hypertension, 2008, 26, 182-186). BPVR is a measure of vascular stiffness that complements currently available indices of Pulse Wave Velocity and the Augmentation Index. These findings support the conclusion that slow breathing exercises can decrease cardiovascular mortality. However, the exercises do not appear to attack the root of causes of hypertension that are vested in renal regulation of blood volume. Additional studies are needed to determine whether more prolonged interventions or, more likely, more intensive interventions that provide feedback to patients for aberrant breathing in the natural environment, have effects on 24-hr blood pressure in hypertensive patients. From such studies may come understanding of the ways in which breathing interventions can affect blood gases, renal sodium regulation, and endogenous digitalis-like factors that interact with high sodium intake to engender chronic salt-sensitive forms of hypertension in humans.