Imaging Dynamic Cellular Events in the Lung

Early in the last century, J.S. Haldane observed, “It is probable indeed that in some way or other the air supply is proportioned to the blood supply, whether by regulation through the muscular coats of the bronchioles or regulation of blood distribution” (Haldane, 1922). Haldane was expressing the opinion that in order to fulfill its essential function of gas exchange (the addition of oxygen and removal of carbon dioxide from the blood), the lung must optimally adjust ventilation and perfusion, requiring the constant regulation of air and blood flows through alterations in the diameter of the supplying conduits. Air and blood are brought in close proximity through separate, highly branched distribution systems that feed gas exchange units (alveoli and alveolar capillaries), whose gas composition is determined by air and blood flow. As the alveoli and pulmonary capillaries consist of millions of exchange units,...