Left ventricular function's relation to load, experimental studies in a porcine model
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Background: Loading conditions are recognized to influence ventricular function according to the Starling relationship for length/stretch and force. Many modern echocardiographic parameters which have been announced as describing ventricular function and contractile status, may be confounded by uncontrolled and unmeasured load. These studies aimed to measure the relation between four different types of assessments of ventricular dysfunction and degrees of load. Study examined the ‘myocardial performance index’ (MPI). Study II examined long axis segmental mechanical dyssynchrony. Study III examined tissue velocities, and Study IV examined ventricular twist. All studies aimed to describe the relation of these parameters both to load and to inotropic changes.
Methods: In anesthetized juvenile pigs, left ventricular (LV) pressure and volume were measured continuously and their relationship (LVPVR) was analysed. Preload alterations were brought about by inflation of a balloon tipped catheter in the inferior vena cava (IVCBO). Inotropic interventions were brought about by either an overdose of anesthetic (combine intravenous pentobarbital and inhaled isoflurane, Study I), or beta blocker and calcium channel blocker given in combination (Studies III and IV). In one study (II), global myocardial injury and dysfunction was induced by endotoxin infusion. MPI measurements were derived from LVPVR heart cycle intervals for isovolumic contraction and relaxation as well as ejection time. Long axis segmental dyssynchrony was derived by analyzing for internal flow and time with segmental dyssynchronous segment volume change during systole, hourly before and during 3 hours of endotoxin infusion. Myocardial tissue velocities were measured during IVCBO at control, during positive and then later negative inotropic interventions. The same for apical and base circumferential rotational velocities by speckle tracking. Load markers (including end-diastolic volume) were identified for each beat, and the test parameters were analysed together with load for a relation. The test parameters were also tested during single apneic beats for a relation to inotropic interventions.
Results: MPI demonstrated a strong and linear relationship to both preload and after-load, and this was due to changes in ejection time, and not the isovolumic intervals. Long axis segmental dyssynchrony increased during each hour of endotoxin infusion and global myocardial injury. This dysynchrony parameter was independent of load when tested by IVCBO. Peak systolic velocities were strongly load-independent, though not in all the inotropic situations and by all measurement axes. Peak systolic strain was load-dependent, and not strongly related to inotropic conditions. Peak systolic LV twist and untwist were strongly load-dependent.
Conclusions: MPI is strongly load-dependent, and can vary widely in value for the same contractile status if the load is varied. Mechanical dyssynchrony measures are load-independen in health and also in early global endotoxin myocardial injury and dysfunction. Peak sytole velocities are a clinically robust parameter of LV regional and global performance under changing load, though peak systolic strain seems to be load-dependent. Left ventricular twist and untwist are load-dependent in this pig model.
Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2011. , 67 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1425
heart function, preload, afterload, contractility, myocardial tissue velocity, speckle tracking
Anesthesiology and Intensive Care
Research subject Cardiology
IdentifiersURN: urn:nbn:se:umu:diva-43605ISBN: 978-91-7459-225-2OAI: oai:DiVA.org:umu-43605DiVA: diva2:414820
2011-05-27, Sal B, 9 tr, Tandläkarhögskolan, Norrlands Universitetssjukhus, Umeå, 13:00 (English)
Brodin, Lars-Åke, Professor
Haney, Michael, MD.PhD.Poelaert, Jan
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