A breathing assistance apparatus includes an inner volumetric member pressurizable from a first pressure to a second pressure and an outer volumetric member surrounding at least a portion of the inner expandable volumetric member. The inner volumetric member pressurizes the outer volumetric member as the inner volumetric member is pressurized from the first pressure to the second pressure. In another embodiment, a breathing assistance apparatus includes exhalation and inhalation chambers with respective biasing members providing for the exhalation chamber to apply a pressure to the inhalation chamber and thereby provide assisted inhalation. Methods for assisting breathing are also provided.