This is an interdisciplinary, interdepartmental Program Project on the physiological basis of pulmonary disease. Research is principally directed toward the mechanisms of ventilation and bloodflow, and studies of gas exchange. Progress has been made on the morphology of muscle capillaries during muscle contraction and extension. In addition, the capillary supply of bird flight muscle has been studied in an effort to improve our understanding of oxygen unloading in tissues that have a high oxygen demand. Both these studies will be extended during the next year of support. Further work is continuing on the multiple inert gas elimination technique for determining distributions of ventilation-perfusion ratios. These studies involving moment analysis will be further extended. An extensive program on oxygen transport during hypothermia has made considerable progress but additional work is planned in the areas of anemic hypoxia and stagnant hypoxia during hypothermia. Work is proceeding on gas exchange in alligator lungs where the effects of stratification are likely to be important. Further experiments on molecular weight dependence of gas exchange in these lungs which form a useful model of some types of human disease are planned. Studies have been carried out on gas exchange in normal man during hypoxic exercise to determine the extent of diffusion impairment, and further work in this area is planned for the coming year. Studies of intermediary metabolism of Harbor seals during rest and exercise have been completed but additional work on energetics in marine mammals, especially using noninvasive procedures, will be carried out.