This means that the maximum volume of water that can be displaced is the volume of the door, Vw=Vd (so that the surface of the door is level with the surface of the water, as in Figure \(\...This means that the maximum volume of water that can be displaced is the volume of the door, Vw=Vd (so that the surface of the door is level with the surface of the water, as in Figure \PageIndex1). Given that the pressure in the patient’s veins is 80 mmHg above atmospheric pressure, we want to find the pressure required at the other end of the needle so that we get the desired flow rate through the needle.
