Heart-lung interactions in mechanical ventilation

Abstract

Understanding heart-lung interaction is critical for hemodynamic evaluation. Since the heart is in the thoracic cavity, it is subject to cyclic changes in airway pressure induced by ventilation. These cyclic changes in airway pressure induce cyclic changes in right and left ventricular (LV) preload and afterload. These occur both in spontaneous ventilation (negative airway pressure) and during mechanical ventilation (positive airway pressure). The cyclic changes have a major impact during cardiac tamponade, right ventricular (RV) failure, and preload dependency. These basic physiological concepts help the clinician differentiate between pericardial effusion without hemodynamic compromise and tamponade, between RV dysfunction and RV failure, and also to detect fluid responsiveness. Heart-lung interactions can be used to predict fluid responsiveness in mechanical ventilation. During inspiration, the increase in pleural pressure increases LV preload as a result of the purge effect on pulmonary veins, decreases RV preload and increases RV afterload, which results in a decrease in RV stroke volume. After a few beats, this results in a decreased LV preload. In volume-responsive patients, these cyclic changes in preload result in cyclic changes in stroke volume. © 2011 Springer-Verlag Berlin Heidelberg.