Cardiac mechanics and energetics--from Emax to PVA

After these seven decades of cardiac mechanics, through the windows of Starling's cardiac output curve followed by Sonnenblick's myocardial force-velocity relation and Vmax, Frank's ventricular pressure-volume (P-V) relationship has revived as a window of cardiac mechanics over the past two decades following the proposal of the Emax concept by Suga and Sagawa. Emax is a physically sound measure of ventricular contractile compressibility or time-varying volume elastance at end systole. Although the original Emax concept has been slightly modified to improve its fitness to reality, the Emax concept has successfully survived over two decades as a basic conceptual framework of ventricular contraction in physiological, pathophysiological and clinical studies. An important expansion of the Emax concept was introduced by Suga a decade ago, and a new window for cardiac energetics was opened up by the concept of PVA as a measure of the total contractile energy generated by ventricular contraction. PVA correlates with ventricular oxygen consumption, with Emax as a decisive parameter. Moreover, Emax and PVA combined with effective arterial elastance Ea as a new afterload parameter proposed by Sunagawa and Sagawa have enabled us to predict cardiac energetics under a variety of loading and contractile conditions. The key advances of the Emax and PVA concepts are reviewed mainly in the biomedical engineering aspects by the proposer of these concepts himself.