Document Detail

Assessment of dsigma*/dt (max), a load independent index of contractility, in the canine.
MedLine Citation:
PMID:  19466542     Owner:  NLM     Status:  MEDLINE    
The search for a load-independent index of myocardial contractility has been a focus for nearly 100 years. Nearly all of the parameters developed have yielded insight into cardiac function but their clinical utility has been limited. A new index, dsigma*/dt (max), has been proposed to be useful in the clinic. This parameter is expressed as the maximum time rate of change of the pressure normalized circumferential wall stress (sigma* = sigma ( theta )/P, where sigma ( theta ) is circumferential wall stress and P is pressure) for a thick walled sphere model of the left ventricle (LV). This definition for a contractility index renders dsigma*/dt (max) dependent only on LV wall volume (V (m)) and maximum time rate of change of the ventricular volume, dV/dt (max). The index dsigma*/dt (max) has been studied in patients with echocardiogram-derived volume, but up until this point its characteristics in canines have remained unknown. Validating this index in the canine will allow for a more intensive and wide-range investigation of the index that is not available with humans. The purpose of this study was to validate dsigma*/dt (max) as a load-independent measure of contractility in the canine heart with the hope that it was a noninvasive assessment of contractile function. To assess the load independence of dsigma*/dt (max), the index was estimated over a range of preloads (end diastolic volume, EDV) during a vena caval occlusion (VCO). The study was conducted in five canines under various pacing modes [right atrial (RA), right ventricular (RV), left ventricular (LV), and biventricular (BV)] at rates of 90 or 100, and 160 bpm. The animals' ventricular volume measurements were assessed by conductance catheter, calibrated with echocardiography. A 50 Hz filter was applied to the volume signal before differentiation to obtain dV/dt (max). Echocardiography was used to calculate left ventricle mass and V (m). In eight of ten cases, dsigma*/dt (max) was significantly correlated with decreasing EDV (p < 0.05). There was also a significant correlation between dsigma*/dt (max) and dP/dt (max). With a strong correlation between the values of dsigma*/dt (max), dP/dt (max), and EDV in all five subjects, dsigma*/dt (max) is not load independent in the canine heart when preload is altered by a VCO. Further evaluation of this index is required to delineate the situations where dsigma*/dt (max) can be accurately applied.
Adam Black; Nathan Grenz; Schaible Niccole; Peter Arndt; Jordan Lucht; Kellen Nesvig; Dan Ewert; Lawrence Mulligan
Publication Detail:
Type:  Journal Article     Date:  2009-05-23
Journal Detail:
Title:  Cardiovascular engineering (Dordrecht, Netherlands)     Volume:  9     ISSN:  1573-6806     ISO Abbreviation:  Cardiovasc Eng     Publication Date:  2009 Jun 
Date Detail:
Created Date:  2009-07-07     Completed Date:  2009-09-22     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101132083     Medline TA:  Cardiovasc Eng     Country:  Netherlands    
Other Details:
Languages:  eng     Pagination:  49-55     Citation Subset:  IM    
Therapy Delivery, Medtronic, Minneapolis, MN, USA.
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MeSH Terms
Blood Pressure / physiology*
Computer Simulation
Heart Rate / physiology*
Models, Cardiovascular*
Myocardial Contraction / physiology*
Stroke Volume / physiology*
Ventricular Function, Left / physiology*

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