Abstract: A self-inflating urinary catheter which includes a retention balloon has a fluid reservoir communicating with the balloon, a wall in the reservoir comprising an elastic membrane arranged to retain fluid in an unpressurized state, a plunger arranged to depress the membrane into the fluid and initially displace part of the fluid and membrane through a window opening in one of the reservoir parts so as to stretch the membrane and pressurize the fluid, thereby exerting force on the fluid to expel if from the reservoir to inflate the retention balloon.

Abstract: A self-inflating urinary catheter which includes a retention balloon has a fluid-filled, unpressurized, deformable reservoir communicating with the balloon. An elastic diaphragm is arranged to squeeze the reservoir against another surface so as to pressurize the fluid, thereby exerting force to expel the fluid from the reservoir to inflate the retention balloon.