After landing, astronauts are often subject to orthostatic intolerance, a cardiovascular abnormality which can cause nausea, vomiting, lightheadedness (presyncope), or fainting (syncope). Previous studies have attributed this intolerance to a reduction in the arterial baroreflex function. This proposed research will further explore this mechanism by studying continuous-time physiological signals collected before and after spaceflight and will be performed under the guidance of NASA researcher Janice Fritsch-Yelle, Head of Cardiovascular Physiology at Johnson Space Center. Utilizing beat-to-beat blood pressure, electrocardiogram, and Doppler ultrasound measurement of aortic blood flow, this research will study the differences in time as subjects move from supine to standing and will analyze the relationship between the different continuous-time measurements.