Figure 4.

The time course of aortic pressure (AP), cardiac output (CO), ventricular volume (VV), and atrial pressure (AtP) if preload is constant (6 mm Hg) and afterload increased from 4 U to 10 U. (a) In initial conditions (20–60 s; afterload is 4 U) all variables are in steady state. Atrial pulse pressure (AtP max/AtP min) is 5.2/3.5 mm Hg. Afterload increased first to 4 U (60–120 s) and then to 10 U (120–180 s). Note that at each step CO is transiently significantly decreased, but within about 20 s it recovers to a new steady state, slightly lower level. Similarly, SV is slightly decreased. AP is increased. AtP max and AtP min are increased to a different extent; therefore, AtP pulse pressure is decreased. After afterload is returned to 4 U, AP, AtP, and VV return to initial conditions level. CO is transiently increased but within about 15 s it also returns to the initial condition level. (b) The P-V loop diagram in conditions above. Note that, if afterload is increased from 4 U to 10 U, ESVV is increased from 39 mL to about 62 mL, while EDVV is increased to a smaller extent, from 117 mL to 127 mL. The EF decreases from 66% to 51%. Ventricular work is given in mm Hg·mL and in J.