Document Detail

Cardiac phase-dependent time normalization reduces load dependence of time-varying elastance.
MedLine Citation:
PMID:  19060125     Owner:  NLM     Status:  MEDLINE    
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.
Taco Kind; Nico Westerhof; Theo J C Faes; Jan-Willem Lankhaar; Paul Steendijk; Anton Vonk-Noordegraaf
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2008-12-05
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  296     ISSN:  0363-6135     ISO Abbreviation:  Am. J. Physiol. Heart Circ. Physiol.     Publication Date:  2009 Feb 
Date Detail:
Created Date:  2009-01-27     Completed Date:  2009-03-12     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  H342-9     Citation Subset:  IM    
Department of Pulmonary Diseases, VU University Medical Center, Amsterdam, The Netherlands.
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MeSH Terms
Heart Catheterization
Heart Rate*
Models, Cardiovascular*
Myocardial Contraction*
Signal Processing, Computer-Assisted
Stroke Volume*
Time Factors
Ventricular Function, Left*
Ventricular Pressure*

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