Poiseuille Award lecture. New trends in biorheology

A trend of engineering approach to physiology is to predict physiological events with mathematical accuracy. In order to achieve this objective, it is necessary to know the structure of the organs and the mechanical properties of their components; i.e., the anatomy, histology, and rheology of the system. Then one must perform the analysis rationally, avoiding ad hoc assumptions as far as possible. To illustrate this aspiration, procedure, labor, and rewards, the case of pulmonary circulation is discussed. For cat lung, anatomical and rheological data were collected; biorheological analysis was done, and physiological experiments were compared with theoretical predictions. Satisfactory results were obtained. The case of flow under zone 2 condition, when "waterfall phenomenon" prevails, is especially interesting. We proved theoretically that any partial collapse of an interalveolar septum is unstable. Hence if a collapse is initiated in an interalveolar septum, the whole septum will be collapsed. From this theoretical result, the pressure-flow relationship is predicted and is shown to agree well with the experiment. New trends toward cell biology and molecular approach are evident in this meeting. Some anticipated trends are, however, still slow in coming.