Pulmonary Structure and Function

The lung, as we now realize, is not a uniform honeycomb ventilated and perfused by homogeneous gas and blood mixtures, nor is it a honeycomb in which any segment is a representative sample of the whole. Instead it is a universe of immensely varied geometrical, physical, and chemical properties in a state of constant flux continually beset by pathogenic stresses. We are, however, just beginning to understand, as a model, some aspects of the lung's structure and function, and the Symposium just about covers the entire field of our present knowledge and ignorance. The emphasis, frequently repeated by the contributors, is on the hybridization of anatomy and physiology in lung studies, and the reader is left with the feeling that, with few notable exceptions, this is still an aim, not a reality. In spite of the desire for a multi-disciplinary approach, most of the papers fall into one or another of four broad categories: (1) anatomy, (2) structural mechanics, (3) gas and blood flow dynamics, and (4) neurogenic control systems. A few deal with more than one of these categories. Progress reported in three specific areas is especially exciting. One of these areas deals with the mechanisms of pulmonary ventilation/perfusion ratios described by several participants. The ventilation/perfusion relationship actually expresses the basic principles of respiratory gas exchange. A second exciting area of progress is the development of a dynamic topology of the alveoli, capillaries, and small bronchioles. Formulation of the forces concerned with bronchial, alveolar, and capillary surfaces remains in the future, but the necessary qualitative and quantitative descriptions are now available. Closely related is the third area of unusual interest, the discovery and description of the surface active substances which have the remarkable property of varying their surfactive characteristics with changes in pressure and gas concentration. This seems to be the key to questions about why alveoli neither collapse nor burst under ordinary conditions. Other topics discussed in this Symposium, such as Krahl's "glomus pulmonale," may prove to be even more important when their significance is known. The discussion printed after each paper is of particular value for this helps to clarify and expand otherwise obscure points. It also serves as a good object lesson in showing how critical we are of weaknesses in another's hypothesis while glossing over the great lacunae in our own, or as Jere Mead, one of the participants, aptly puts it, "one man's artifact is another man's assumption." I can think of no way more effective and enjoyable to bring one's knowledge of the lung right up to the brink of tomorrow than to read this book. The impatient reader should concentrate on Liebow's opening paper, and Richard's closing summary.