ABSTRACT
To the best of our knowledge, Stephen Hales gave the first description of heart-lung interactions at the beginning of the 18th century. After inserting a glass tube in the carotid artery of a mare, he observed that the height of the column of blood fluctuated with respiratory movements and raised the hypothesis that these changes were the consequence of an effect of respiratory effort on venous return (1). Since this landmark experience, many authors have investigated the mechanisms by which lung physiology can have an impact on heart physiology. Heart-lung interactions result intrinsically from heart and lung anatomy: the cardiac chambers are subject to intrathoracic pressure (ITP), in particular to its changes; the right ventricle (RV) is directly connected upstream of the lung and is likely to be subject to alterations in lung circulation; lung circulation in the pulmonary capillaries is subject to distending pressure of the lung, which is also called transpulmonary pressure (TPP); and finally, the two ventricles share a common wall, which is the interventricular septum. These characteristics underpin explanations of how heart-lung interactions work.
