A medical device such as a controlled discharge ostomy appliance comprises a fluid filled seal for sealing around a body orifice (stoma). The fluid filled seal comprises a fluid chamber including a fluid impermeable membrane that forms a movabable wall of the fluid chamber, one or more ports communicating with the chamber； and resilient foam disposed within the fluid chamber. The foam tends to expand the chamber to seal against the body. The port controls the inlet and exhaust of fluid from the chamber, in response to movement of the body away from, or towards, the seal.
