Analysis of left ventricular hemodynamics in physiological hyperspace.

Our laboratory has previously shown that it is possible to elucidate novel physiological relationships by analyzing the left ventricular pressure (P) contour in the phase [time derivative of P (dP/dt) vs. P] plane (Eucker SA, Lisauskas JB, Singh J, and Kovács SJ, J Appl Physiol 90: 2238-2244, 2001). To further characterize cardiac physiology, we introduce a method that combines P-volume (V) and phase plane-derived information in physiological hyperspace. From four-dimensional (P, V, dP/dt, time derivative of V) hyperspace, we consider three-dimensional embedding diagrams having dP/dt, P, and V as coordinate axes. Our method facilitates analysis of physiological function independent of inotropic state and permits assessment of P-V-based relationships in the phase plane and vice versa. To test feasibility, the method was applied to murine hemodynamic data. As predicted from first principles, the area of the P-V loop (ventricular external work) correlated closely (r = 0.97) with phase plane limit cycle area (external power). The P-V plane-derived linear (r = 0.99) end-systolic P-V relationship (maximum elastance) appeared linear in the phase plane (r = 0.85). We conclude that analysis of data in physiological hyperspace is generalizable: it facilitates quantitative characterization of ventricular systolic and diastolic function and can guide discovery of novel physiological relationships.