Document Detail

Limitations of R-average as an index of left ventricular isovolumic relaxation.
MedLine Citation:
PMID:  8846665     Owner:  NLM     Status:  MEDLINE    
Freeman et al. (1993) have recently introduced a new index measuring isovolumic relaxation in the in situ left ventricle. This index, called the R-average, shows less variability than the traditionally used monoexponential time constant (tau), and could therefore represent an alternative measure of isovolumic relaxation during different physiological or pathophysiological interventions. However, the R-average represents the average pressure fall during isovolumic relaxation (isovolumic pressure fall divided by the isovolumic time period), and is therefore highly influenced by the end-systolic pressure level. The present study was done in order to assess whether small increments in loading conditions would alter the R-average without changes in the isovolumic relaxation period or the monoexponential pressure decay tau. We used a right heart bypass porcine model, and end-systolic pressure was altered between 92 and 140 mmHg by pre-loading (servo-pump) or after-loading (phenylephrine) in spontaneously beating and paced hearts. During loading, we found a significant increase in the R-average and a close correlation (r = 0.72 - 0.99) between R-average and en-systolic pressure. However, no alterations were found in the duration of the isovolumic relaxation time period or monoexponential pressure decay (tau) during these loading conditions. In our view, the R-average indicates the systolic loading level for the ventricle, but does not necessarily reflect alterations in the process of active relaxation.
T Myrmel; I B Krukenkamp; C A Caldarone; P A Burns; G Gaudette; S Levitsky
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Clinical physiology (Oxford, England)     Volume:  15     ISSN:  0144-5979     ISO Abbreviation:  Clin Physiol     Publication Date:  1995 Sep 
Date Detail:
Created Date:  1996-10-24     Completed Date:  1996-10-24     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8309768     Medline TA:  Clin Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  447-58     Citation Subset:  IM    
Division of Cardiothoracic Surgery, New England Deaconess Hospital, Boston, MA 02215, USA.
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MeSH Terms
Blood Pressure / physiology*
Muscle Relaxation / physiology*
Statistics as Topic
Time Factors
Ventricular Function, Left / physiology*
Grant Support

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