Pressure and Volume Characteristics of the Left Ventriclе in Its Diastolic and Systolic Dysfunction

Abstract

Cardiomyopathy in rats has been developed after 4 weeks doxorubicin administration(2 mg / kg weekly). Echocardiographic study of rats in 8 weeks from onset of doxorubicin administration showed preponderanceof systolic dysfunction (67 %) with decrease of left ventricular (LV) ejection fraction (EF) by 30 %. Simultaneous registration of LV pressureand volume showed that diastolic LV volume was preserved in doxorubicin-treated rats due to considerable lengthening of the diastole,the heart rate was reduced by 22 %. These hearts also showed slowing of relaxation, reduced maximal rate of pressure development andstroke work, as well as significant reduction in peripheral arterial resistance. Diastolic dysfunction differed from the systolic one by normalsystolic EF and preserved LV contractility index as well as lower diastolic LV pressure throughout the diastole. Based on thesedata, four compensatory mechanisms associated with cardiomyopathy were distinguished - 1) slowing of myocardial relaxation, prolongingmyofibrillar active state, 2) reduction of peripheral arterial resistance for easier LV ejection, 3) heart rate reduction, prolonging diastolicpause and thus facilitating better LV filling and 4) increased pressure in the small circle, also contributing to the LV rapid filling.