[Hemodynamics in ischemia: diastolic phase]. / Hämodynamik unter Ischämie: Diastolische Phase.

ABSTRACT

The diastolic portion of the cardiac cycle can be divided into sequential phases isovolumic ventricular relaxation; rapid ventricular filling; slow, or passive, ventricular filling; and atrial contraction. Contraction and relaxation are to some extent interrelated; however, relaxation is not simply a passive reversal of events during systole. Rather, relaxation is an energy-consuming process which involves dissociation of calcium from the actin-myosin-complex and reuptake of calcium by the sarcoplasmic reticulum. Left ventricular diastolic function is determined by the interrelationship of several/factors, including some intrinsic to the left ventricular chamber (completeness of left ventricular relaxation, time course of left ventricular contraction, and elastic and viscous properties of the myocardium) and others extrinsic to the left ventricle (pericardial and pleural pressure, right ventricular contraction, and coronary perfusion pressure). Acute ischemia alters diastolic left ventricular function by slowing isovolumic relaxation, delaying left ventricular filling and altering passive elastic properties of the myocardium. Slowing of isovolumic relaxation is measured as a fall in the maximal rate of left ventricular pressure decline (peak negative dP/dt) and as an increase in the time constant (T) of left ventricular pressure fall. Delayed left ventricular filling is manifested regionally as a reduced rate of septal and posterior wall thinning (by echocardiography) and globally as a reduced rate of chamber filling (by gated radionuclide angiography).(ABSTRACT TRUNCATED AT 250 WORDS)