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This Article Full Text Full Text (PDF) All Versions of this Article: 296/2/H342    most recent 00785.2008v1 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 Web of Science 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 Kind, T. Articles by Vonk-Noordegraaf, A. Search for Related Content PubMed PubMed Citation Articles by Kind, T. Articles by Vonk-Noordegraaf, A.

Cardiac phase-dependent time normalization reduces load dependence of time-varying elastance

Departments of ¹Pulmonary Diseases, ²Physics and Medical Technology, and ³Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam; and ⁴Department of Cardiology, Leiden University Medical Center, Leiden, the Netherlands

Submitted 29 July 2008 ; accepted in final form 1 December 2008

The time-varying elastance concept provides a comprehensive description of the intrinsic mechanical properties of the left ventricle that are assumed to be load independent. Based on pressure-volume measurements obtained with combined pressure conductance catheterization in six open-chest anesthetized sheep, we show that the time to reach end systole (defined as maximal elastance) is progressively prolonged for increasing ventricle pressures, which challenges the original (load-independent) time-varying elastance concept. Therefore, we developed a method that takes into account load dependency by normalization of time course of the four cardiac phases (isovolumic contraction, ejection, isovolumic relaxation, filling) individually. With this normalization, isophase lines are obtained that connect points in pressure-volume loops of different beats at the same relative time in each of the four cardiac phases, instead of isochrones that share points at the same time in a cardiac cycle. The results demonstrate that pressure curves can be predicted with higher accuracy, if elastance curves are estimated using isophase lines instead of using isochrones [root-mean-square error (RMSE): 3.8 ± 1.0 vs. 14.0 ± 7.4 mmHg (P < 0.001), and variance accounted for (VAF): 94.8 ± 1.3 vs. 78.6 ± 14.8% (P < 0.001)]. Similar results were found when the intercept volume was assumed to be time varying [RMSE: 1.7 ± 0.3 vs. 13.4 ± 7.4 mmHg (P < 0.001), and VAF: 97.4 ± 0.5 vs. 81.8 ± 15.5% (P < 0.001)]. In conclusion, phase-dependent time normalization reduces cardiac load dependency of timing and increases accuracy in estimating time-varying elastance.

ventricular loading; cardiac time course; isochrones; isophase lines