Document Detail

Interaction between afterload and contractility in the newborn heart: evidence of homeometric autoregulation in the intact circulation.
MedLine Citation:
PMID:  7722145     Owner:  NLM     Status:  MEDLINE    
OBJECTIVES: We undertook the present study to determine whether afterload and contractility interact in the hearts of newborn lambs. We specifically investigated whether stepwise increases in afterload increase contractility. BACKGROUND: Several studies in the isolated and intact adult dog heart have shown that afterload and contractility are not independent determinants of cardiac performance; rather, they interact. Afterload and contractility are unlikely to interact in the newborn heart because the factors that may mediate the interaction in the adult are missing in the newborn. METHODS: We measured contractility at different steady state levels of afterload in seven newborn lambs under complete anesthesia. Contractility was measured by three different indexes: end-systolic pressure-volume relations (slope and volume position); preload-corrected first derivative of left ventricular pressure (dP/dtmax); and preload-corrected stroke work. Left ventricular pressure and volume were measured with a micromanometer and conductance catheter, respectively. Preload and afterload were manipulated by inflating or deflating a balloon catheter in the inferior vena cava and descending thoracic aorta, respectively. Data are expressed as mean value +/- 1 SD. RESULTS: Stepwise increases in afterload increased contractility, independent of which of the three indexes was used. The slope of the end-systolic pressure-volume relation increased from a mean baseline value of 4.44 +/- 2.43 to 6.69 +/- 2.89 kPa/ml at the highest level of afterload. Concomitantly, volume at 14 kPa of the end-systolic pressure-volume relation decreased from 3.34 +/- 1.52 ml at baseline to 1.12 +/- 0.83 ml at the highest afterload. The other two indexes showed qualitatively similar changes. Beats selected from unloading interventions on the basis of the same end-diastolic volume for each level of afterload showed no difference in stroke volume. CONCLUSIONS: This study in newborn lambs demonstrates that stepwise increases in afterload increase contractility considerably and that this enables the heart to maintain stroke volume at different levels of afterload. This forms direct evidence for the existence of homeometric autoregulation in the intact newborn heart.
R J Klautz; D F Teitel; P Steendijk; F van Bel; J Baan
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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:  Journal of the American College of Cardiology     Volume:  25     ISSN:  0735-1097     ISO Abbreviation:  J. Am. Coll. Cardiol.     Publication Date:  1995 May 
Date Detail:
Created Date:  1995-05-25     Completed Date:  1995-05-25     Revised Date:  2010-03-24    
Medline Journal Info:
Nlm Unique ID:  8301365     Medline TA:  J Am Coll Cardiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1428-35     Citation Subset:  AIM; IM    
Department of Pediatrics, Leiden University Hospital, The Netherlands.
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MeSH Terms
Analysis of Variance
Animals, Newborn
Aorta, Thoracic
Balloon Dilatation
Blood Pressure / physiology
Constriction, Pathologic
Homeostasis / physiology*
Linear Models
Myocardial Contraction / physiology*
Stroke Volume / physiology
Vena Cava, Inferior
Ventricular Function, Left / physiology*

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