I am a medical doctor needing some physics help. Quite often in patients we insert thin tubes into blood vessels for various purposes. These occasionally get blocked and we use syringes to try and clear these blockages. We attach a syringe and create a "negative pressure" by drawing back the plunger. Some of my colleagues claim that one can generate a more negative pressure with a syringe (piston) with a smaller diameter. Others claim that a piston with a larger diameter can generate a stronger negative pressure. So here is my question: For a given "pulling force" on the plunger of a piston, does the diameter of the piston influence the degree of negative pressure generated by the piston. I do know that according to the equation pressure = force/area, smaller diameters generate higher pressures. But does this hold true even when trying to generate a negative pressure with a syringe? Your help will be much appreciated and may help save lives. Following this posting i did a small experiment. I hung an one kilo weight on a 5 ml and 10 ml syringe and connected it to a Digitron electronic manometer. I got the following neg pressure readings (cm Hg). The 5 ml syringe: 57.3;55.8;56.7;56.6;55.9;56.6;57.4;56.1;56.1;56.6 The 10 ml syringe gave the following: 32.8;32.3;30.7;31.9;31.9;32.6;30.6;33.3;32.1;30.5 I would like to"scientifically" say that the smaller syringe creates a bigger negative pressure. My statistical knowledge is near zero. Would a "Students t" test be an appropriate one to use ?