Figuring out why we breathe

This paper chronicles the evolution of present understanding of cardiopulmonary physiology and attempts to illuminate both the thought and innovation of all the participating pioneers. Early on, the rate of progress was determined by advances in anatomy-the definition of the vascular system and its relationships to the heart and lungs. It was held back by concerns, especially religious, with the pneuma, and by ignorance of the inability of air and blood to circulate together, and of blood's capability to transport gases within its cells. These stumbling blocks were set aside successively by the advent of microscopic anatomy (red cells and capillaries), chemistry (hemoglobin structure and function; the fact that air is a mixture of gases of different properties; processes of combustion; and the theory of the conservation of matter), and physics (Bohr effect; molecular structure of hemoglobin). Only through access to these facts and principles have we been able to approach some inborn errors and to design molecular prostheses such as oxygen-carrying microspheres and polyethylene glycol-hemoglobin.