Fig. 2
Equation for estimating EDV. A Schematic diagram of a pressure–volume loop, end-systolic pressure–volume relationship (slope of end-systolic elastance [Ees]), arterial pressure–volume relationship (negative slope of effective arterial elastance [Ea]), end-systolic pressure (Pes), ventricular pressure at which the ventricle begins to eject (Pad), and putative isovolumic pressure (Pmax) (left). The figure on the right shows the left ventricular elastance (E(t)) of systole only, approximated with lines for the pre-injection period (PEP) and ejection time (ET), respectively. The ratio of the slopes of those two lines (tanθ1/tanθ2) is expressed as a constant (k) (right). See reference [1] for details. B Trace of the left ventricular volume of one heartbeat. The y-axis shows pressure, and the x-axis shows volume. In the figure, this is expressed as Ea = Pes/SV, Ees = Pes/(ESV-V0) = Pes/(EDV-SV-V0). From Ees/Ea = SV/(EDV-SV-V0), this becomes EDV = SV (1 + Ea/Ees) + V0. It was assumed that V0 is equal to zero. Therefore, EDV = SV (1 + Ea/Ees)