A breast pump device and associated methods for extracting breast milk are disclosed. A pump head comprises an external shell with an elastic membrane disposed and bonded therein to define at least one hermetically sealed chamber. Manipulation of the elastic membrane, for example, by adjusting suction or pressure in the sealed chamber or within an interior volume defined by the elastic membrane permits radial mechanical compression (positive pressure) to be applied to a nipple positioned in the pump head to simulate compression of the nipple by the infant's tongue and simultaneously permits axial hydraulic or pneumatic suction (negative pressure) to be applied to the nipple to simulate the infant's minimum intra-oral vacuum. The breast pump device of the present invention can generate these simultaneous compressions and suctions with a single vacuum source, which may be an electric pump or a hand-operated mechanical pump.