Orthostatic intolerance remains a problem upon return to Earth from the microgravity environment of spaceflight. To improve astronaut's countermeasure programs, a better understanding of the response of the cardiovascular system to changes in hydrostatic pressure is crucial. My objective is to assess the regulatory mechanisms of the microcirculation in response to hydrostatic pressure by combining in vivo experiments and 1D blood pressure wave propagation model. At the Aerospace Physiology Laboratory of SFU, I will perform in vivo experiments using a tilt table and a Low Body Negative Pressure set-up to generate a step and linear increases in the hydrostatic pressure. Quadratic increases in hydrostatic pressure will be generated with a Short Arm Human Centrifuge at the Space Physiology division of the DLR. Combining these three protocols will allow me to differentiate responses to abnormal hydrostatic loads (step and quadratic increases) from a linear gradient in hydrostatic pressure normally felt on earth. High resolution ultrasound imaging techniques will be used to measure hemodynamical parameters of large vessels. Concurrently, the theoritical effects of hydrostatic pressure will be implemented in a 1D wave propagation model of blood flow and pressure to simulate the cardiovascular response to the in vivo protocols described above. Furthermore, a fitting process between in-vivo data and simulated data will provide physiological parameters describing the specific vasoconstriction responses of the peripheral bed to the different hydrostqtic loads. The results of this project will bring new insights into the response of the cardiovascular system to changes in hydrostatic pressure which are essential to improve astronaut's training programs and resolve crucial issues in hypotension and peripheral vascular diseases. This project will enable me to make an important step towards my career objective to become an established researcher in the field of space physiology.