THE EFFECT OF ACUTE NORMOVOLEMIC HEMODILUTION (ANH) ON MYOCARDIAL-CONTRACTILITY IN ANESTHETIZED DOGS

The influence of severe acute normovolemic hemodilution (ANH) on myoca rdial contractility (MC) was investigated in 14 splenectomized, anesth etized dogs. MC was assessed by the maximum rate of left ventricular p ressure increase (LVdp/dt(max)), end-systolic elastance (Ees), and pre load recruitable stroke work (PRSW) (conductance catheter, left ventri cular pressure-volume relationship). Measurements of myocardial perfus ion and oxygenation (radioactive microsphere technique) assured compar ability of the model to previously performed studies. Global and regio nal myocardial blood flow increased significantly upon hemodilution wi th preference to midmyocardium and subendocardium. This resulted in pr eservation of both myocardial oxygen delivery and consumption after AN H. Myocardial oxygen extraction as well as coronary venous PO2 were un affected by ANH, while coronary venous lactate concentration decreased , indicating that myocardial oxygen need was met. LVdp/dt(max) decreas ed significantly after hemodilution (2278 +/- 577 vs 1884 +/- 381 mm H g/s, P < 0.01), whereas Ees and PRSW increased significantly (1.76 +/- 0.54 vs 2.15 +/- 0.75 mm Hg/mL, P < 0.05, for Ees and 33 +/- 14 vs 45 +/- 14 mm Hg . mL, P < 0.05, for PRSW). While the decrease of LVdp/dt (max) most likely reflects ANH-induced changes of ventricular pre- and afterload, the increase of Ees and PRSW indicates a true increase of myocardial contractility during ANH in anesthetized dogs.