Answer:
If you plan to cook the artichokes whole, first remove the other leaves, and open the center delicately to remove the choke. Then, put the steamer basket in your pressure cooker (if you don't have one those metal foldable ones that open like flowers will do) add two cups of water with a squirt of lemon. Place the artichokes on the steamer basket inside the pressure cooker face up. Close and lock the top. Turn the flame to high and when it begins to whistle (actually it's more like a hiss) turn the heat down to low and count 10-12 minutes. At which point turn off the heat, release all of the vapor, open the pan and enjoy your artichokes!