DK2985_C000 1..28 - AlSharqia Echo Club

Global Ventricular Function and Hemodynamics 187Figure 9.2 (A) Changes in aortic,atrial, ventricular pressure, and ventricularvolume in relation to the electrocardiogram.Left ventricular (LV)pressure and volume over timeduring a cardiac cycle is characterizedby seven time-related events. Isovolumiccontraction [1] is followed byearly [2] and late [3] ejection. Diastolestarts with isovolumic relaxation [4]followed by the early filling phaseafter the opening of the mitral valve[5], diastasis [6], and atrial contraction[7]. (B) Corresponding LV pressure–volume relationship during onecardiac cycle.these determinants will affect the pressure–volumerelationship differently. In the following discussion,when possible, the effects of changes in cardiac functionand their determinants will be explained by using thepressure–volume relationship.1. PreloadA decrease in preload will be associated with a fall inLVEDV and LVEDP [Fig. 9.4(A)]. It is difficult clinicallyto differentiate between hypovolemia from reduced(~ SAP) LVESPStroke volume = CO/HRLV PressureStroke WorkLVEDP(~ Wedge)LV Volume(~ ES Area) (~ ED Area)Figure 9.3 Left ventricular (LV) pressure–volume relationship during one cardiac cycle. The LV end-systolic pressure (LVESP) canbe estimated using systolic arterial pressure (SAP) and the LV end-diastolic pressure (LVEDP) can be estimated with the pulmonaryartery-derived “wedge” pressure at end-diastole. Using echocardiography, the LV end-systolic (ES) volume can be estimated with theES area and the LV end-diastolic (ED) volume can be estimated with the ED area. The stroke volume, which is the differencebetween the ED volume and the ES volume, can be calculated from the ratio of the cardiac output (CO) obtained by Doppler or thermodilutiondivided by heart rate (HR). The LV stroke work corresponds to the area under the LV pressure–volume diagram (gray area).Changes in compliance of the left ventricle can explain why filling pressure does not always correlate with ventricular size.