The purpose of the present proposal is to study the dynamics of gas exchange at the levels of the lung, blood, and tissue. The following studies are proposed: 1) To detect and quantify normal periodic changes in ventilation/perfusion ratio distribution in the lung during the steady state; 2) To measure changes in ventilation/perfusion ratio distribution in response to environmental stress; 3) To quantify interrelations between oxygen saturation, carbon dioxide, hydrogen ion, 2,3-diphosphoglycerate, temperature and oxygen affinity; 4) To develop a digital computer model of 02, CO2, H plus, DPG, and hemoglobin interrelationships; 5) To model tissue gas exchange; 6) To quantify the influence of oxygen affinity on maximum tissue oxygen delivery; 7) To measure the diffusion coefficients of various inert gases in tissue, and 8) To quantify the transient state diffusion of inert gas in tissue.