A blood pressure measurement device (12) has an inflatable chamber (20) with a variable inflation level for applying a controllable pressure to a part (16) of a subject's body, and a volume varying arrangement (24) for inducing an additional change in an internal volume of the chamber (20) without altering a quantity of fluid inside the chamber. A controller (32) is configured to execute a volume change procedure using the volume varying arrangement, wherein one or more defined volume changes are induced in the chamber, with the fluid quantity kept the same. An internal pressure change response inside the chamber is simultaneously monitored. An output is then generated based on the sensed pressure changes. In some examples, a pressure versus volume relationship for the inflatable chamber (20) may be generated and output.
