Hi everyobdy. First, forgive me for mistakes, since English is not my native language. I'm going to ask a kinda strange question, so let me add a short premise. I'm a first grade MD, andrology will be my area of expertise. I have to give an advice about a patient who has Peyronie' disease (penis with a pronounced curve, basically) . This disease has been treaten with chemicals and mechanical therapy; more specifically, I'm going to prescribe a vacuum device. One of my fellows argues that water-based pumps will provide a better outcome. His argument is that, for any given level of negative pressure, say 5hg, the expansion in the penis will be certainly more noticeable if the vacuum is generated by water than if generated by air. I do understand that, being air not expandable at that pressure (differently than air) the space created, so to speak, by the water which is pulled out, will be filled entirely with the penis; where I differ, is the final outcome, after about 20 minutes : my reasoning is that, slowly (let's suppose the pressure has dropped to 3hg in both scenarios), the density of water will posite a limit to the expansion of the penis; since water is hard to compress, where air is not, after a while the penis will have to fight an higher compressive force if imersed in water than if in a air-generated vacuum. I do believe also that the same higher compressive force of water, in hand with the bouyancy, will cause more length expansion in the water vacuum than in air and more girth expansion in air than in water (this is a secondary question, though). Hope my question is clear. I'd like to hear a very simple explanation and if possible an opinion from somebody whith an operative, professional experience in a related field. Thanks to everybody in advance for the help.