Head-up tilt is a technique used to test orthostatic reflexes with the use of leg skeletal muscle pump activity. The participant is tilted from a supine position to an angle of 70 degrees. They are monitored in this position until the end of the test or when the participant becomes presyncopal. The picture on the left is from a head-up tilt experiment conducted in the altitude chamber at SFU at an altitude of 3660 m. The following article was published from that study: 

Blaber, A.P., Hartley, T., and Pretorius, P.J. (2003). Effect of acute exposure to 3,660 m altitude on orthostatic responses and tolerance. J. Appl. Physiol. 95:591-601. PMID 12716872