Heart-lung interactions: An overview

The respiratory and circulatory systems act in concert to deliver oxygen to the periphery from the atmosphere and carbon dioxide from the periphery to the atmosphere. The end game is played out at both ends of the field: at the microcirculatory and cellular level during normal function, disease states, and exercise, and at the alveolar capillary membrane (Chapters 6, 9). Since the 19th century, there has been the realization that these two systems interact with each other on many levels. There are interesting evolutionary aspects to this since these systems embryologically derive from different tissues, the respiratory system from foregut and the circulatory system from the mesenchyme. Nevertheless, evolution has driven these two systems to work together and to be connected in numerous intimate ways toward a common goal. The many levels at which the respiratory and circulatory systems interact and influence each other have been the subject of intense investigation. The levels of interaction include neurological, humoral, and mechanical. There are a number of disease conditions in which the interaction of these systems is important and the clinician needs to be aware of them. The purpose of this chapter is not so much to impart specific facts about each topic (this is done in the subsequent chapters to which the reader is referred for detailed review and references) but to give an appreciation of the complexity of the coordination of respiratory and cardiovascular systems