Some comments on ventricular afterload.

In this issue of Basic Research in Cardiology a paper by Timisjärvi et al. is presented in which the problem of afterload, generated by the resistance against which the left ventricle is ejecting, is discussed. These authors have performed experiments in which they examine the role and validity of the so-called mean outflow resistance (MOR) of the left ventricle. In this editorial, the opportunity is taken to present some thoughts on the different possibilities of expressing the interrelation between the heart and the arterial system. It is intended to show how, from the first ideas about ventricular-arterial interaction bei Ph. Broemser (1935; 1) different concepts about simple descriptions of the functioning of the heart, the arterial system and the matching between both have evolved. In particular, the concept by Sunagawa et al. seems worthy of mention. An examination of this, and several other concepts, prove that the peripheral resistance and, particularly, the MOR, are important parameters that determine the influence of the arterial system on the performance of the heart. However, since MOR by definition is closely related to the total peripheral resistance, there is no essential need to introduce this resistance as a new concept of ventricular afterload. Calculations based on this definition of MOR demonstrate an agreement between theory and experimental results.