Phase plane analysis of isovolumic relaxation

Traditional analysis of the cyclic left ventricular (LV) pressure contour utilizes only a small amount of its total information content. For optimal quantitation of LV function maximal information extraction from the contour is desirable. To achieve this, we utilized phase plane analysis to characterize τ, the time constant of isovolumic relaxation. Exponential pressure decay in time appears as a linear relation in the phase plane (dP/dt vs P). The cyclic LV pressure generates a limit cycle in the phase plane, whose isovolumic relaxation portion was analyzed to elucidate the pressure decay process. In 4 of 19 subjects isovolumic pressure decline could not be accurately fit using the standard exponential decay assumption. Hence, phase plane analysis provides new information about isovolumic relaxation.