## Abstract

In current practice, empirical parameters such as the monoexponential time constant τ or the logistic model time constant τ_{L} are used to quantitate isovolumic relaxation. Previous work indicates that τ and τ_{L} are load dependent. A load-independent index of isovolumic pressure decline (LIIIVPD) does not exist. In this study, we derive and validate a LIIIVPD. Recently, we have derived and validated a kinematic model of isovolumic pressure decay (IVPD), where IVPD is accurately predicted by the solution to an equation of motion parameterized by stiffness (E_{k}), relaxation (τ_{c}), and pressure asymptote (P∞) parameters. In this study, we use this kinematic model to predict, derive, and validate the load-independent index M_{LIIIVPD}. We predict that the plot of lumped recoil effects [E_{k}·(P_{max}* - P∞)] versus resistance effects [τ_{c} · (dP/dt_{min})], defined by a set of load-varying IVPD contours, where P_{max}* is maximum pressure and dP/dt_{min} is the minimum first derivative of pressure, yields a linear relation with a constant (i.e., load independent) slope M _{LIIIVPD}. To validate the load independence, we analyzed an average of 107 IVPD contours in 25 subjects (2,669 beats total) undergoing diagnostic catheterization. For the group as a whole, we found the E_{k}· (P_{max}* - P∞) versus τ_{c} · (dP/dt_{min}) relation to be highly linear, with the average slope M_{LIIIVPD} = 1.107 ± 0.044 and the average r^{2} = 0.993 ± 0.006. For all subjects, M_{LIIIVPD} was found to be linearly correlated to the subject averaged τ (r^{2} = 0.65), τ_{L}(r^{2} = 0.50), and dP/dt_{min} (r^{2} = 0.63), as well as to ejection fraction (r^{2} = 0.52). We conclude that M_{LIIIVPD} is a LIIIVPD because it is load independent and correlates with conventional IVPD parameters. Further validation of M _{LIIIVPD} in selected pathophysiological settings is warranted.

Original language | English |
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Pages (from-to) | H2551-H2559 |

Journal | American Journal of Physiology - Heart and Circulatory Physiology |

Volume | 295 |

Issue number | 6 |

DOIs | |

State | Published - Dec 2008 |

## Keywords

- Hemodynamics
- Isovolumic relaxation
- Mathematical modeling