Developed for use in space by NASA in 1969.  From US patent #3,420,225.

“Accordingly, an object of this invention is to provide an improved spirometer which will operate properly even under the influence of acceleration forces in any direction.”

“By way of brief description, a balanced bellows spirometer according to the invention comprises a center wall with a bellows mounted on each side of the wall. The bellows are pivotally connected to opposite edges of the center wall and a passage through the center wall interconnects the two bellows chambers into one composite chamber. An inlet is provided into one bellows and an outlet is provided from the other bellows. The two bellows are mechanically interconnected so that the tendency of either bellows to move toward or away from the center wall under the influence of acceleration forces is resisted by an equal and opposite tendency of the other bellows to move under the influence of said acceleration. As a result, the bellows are not moved by acceleration forces and yet are free to expand and contract under the forces of air pressure.”