Disclosed are compounds of formula Ior a stereoisomer, tautomer, or pharmaceutically acceptable salt or solvate thereof, U, W, X, R1, R2, R6, R7, R30 and R31 are as described above in the specification. A first image acquisition system is configured to produce a fluoroscopy image of an anatomical region. On an upstroke lower production fluid is drawn from the lower level into the lower chamber through a lower intake, and upper production fluid in the upper chamber is forced up the tube toward ground surface.