One possibility for the transhuman design concept involves a modification of the current human respiratory system--the lungs and air passageways. Our own form is, while rather efficient, not quite as superb as that of birds. Our particular use of air sacs means that we only absorb about 20% of the oxygen we inhale--the other 80% are released immediately in the same breath. Bird lungs make use of various air sacs as well, but in an arrangement of air flow so as to make updake of oxygen and release of carbon dioxide for efficient.