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This Article Full Text Full Text (PDF) All Versions of this Article: 295/6/H2551    most recent 00780.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Shmuylovich, L. Articles by Kovács, S. J. Search for Related Content PubMed PubMed Citation Articles by Shmuylovich, L. Articles by Kovács, S. J.

Stiffness and relaxation components of the exponential and logistic time constants may be used to derive a load-independent index of isovolumic pressure decay

Cardiovascular Biophysics Laboratory, Cardiovascular Division, ¹Department of Internal Medicine, ²Department of Physics, College of Arts and Sciences, ³Division of Biology and Biomedical Sciences, Washington University School of Medicine, Saint Louis, Missouri

Submitted 24 July 2008 ; accepted in final form 17 October 2008

In current practice, empirical parameters such as the monoexponential time constant or the logistic model time constant _L are used to quantitate isovolumic relaxation. Previous work indicates that and _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 (_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 [_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 _c·(dP/dt_min) relation to be highly linear, with the average slope M_LIIIVPD = 1.107 ± 0.044 and the average r² = 0.993 ± 0.006. For all subjects, M_LIIIVPD was found to be linearly correlated to the subject averaged (r² = 0.65), _L(r² = 0.50), and dP/dt_min (r² = 0.63), as well as to ejection fraction (r² = 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.

isovolumic relaxation; mathematical modeling; hemodynamics