An apparatus and method determine change in volume of a body part or body organ on a real-time basis. In a breastfeeding application, an inflatable cuff is positioned on a nursing breast and allows direct access to the nipple by the breastfeeding infant. The inflatable cuff includes an outer shell portion and an inner inflatable cuff or bladder. The pressure in the inflatable cuff is monitored regularly by a pressure sensor, during a breastfeeding session. When the pressure drops below a preselected pressure, a controller directs a pump to pump air into the inflatable cuff to maintain the preselected pressure. The volume of added air is monitored during the breastfeeding session. Various calibrations are used to correlate the amount of added air, to the volume of breast milk withdrawn from the breast. The volume of breast milk withdrawn during breastfeeding is calculated and displayed throughout the breastfeeding session.
