Abstract 14597: Normalized Pressure Phase Plane Analysis Reveals Invariant Properties of Isovolumic Relaxation
Background: To fit the left ventricular (LV) isovolumic relaxation contour after minimum dP/dt, an exponential decay with time constant τ is assumed. A simple graphical method to calculate τ is provided by the pressure phase plane (PPP), spanned by the rate of change in pressure (dP/dt) vs. pressure (Fig.1 -C). LV relaxation has been previously characterized in the PPP. To reveal the underlying mechanisms of relaxation we define the normalized PPP (NPPP) as follows: 0≤P≤1 and -1≤dP/dt≤+1 (Fig 1.D). This eliminates the effect of load on P and dP/dt. We calculated the normalized pressure when peak -dP/dt (PN,-1) is reached and its associated normalized τ value (τn). We hypothesize that the normalized τ value is a physiologic invariant among subjects and it can be used to accurately predict the actual τ value.
Methods: Pressure data for 10 subjects was plotted in the NPPP (1352 beats). For each subject PN,-1 and τn for each beat was calculated and averaged. For validation τn per beat provided average τn for all 10 subjects. We derived the mathematical relationship between τn and actual τ and used the relationship to estimate the actual τ (τAvg_Calc) of each subject.
Results: The mean and variance for τn was 0.713 ± 0.0035 and τAvg_Calc showed excellent correlation with actual τ for each subject (R2 = 0.87, Fig. 1E).
Conclusion: Computing τn in the NPPP, reveals that τn is essentially invariant among subjects. The mean τn (0.713) can be used to estimate actual τ with very little error (mean absolute error = 0.004 s) and the calculated values (τAvg_Calc) correlate very well with the measured (MILLAR) τ values. Hence NPPP analysis of hemodynamic data removes load related P and dP/dt effects and reveals the underlying, load-independent dynamic attributes of isovolumic relaxation. .
- © 2012 by American Heart Association, Inc.