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Relevance of the volume‐axis intercept, V 0 , compared with the slope of end‐systolic pressure–volume relationship in response to large variations in inotropy and afterload in rats
Author(s) -
Blaudszun Grégoire,
Morel Denis R.
Publication year - 2011
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2011.059881
Subject(s) - dobutamine , preload , inotrope , afterload , contractility , medicine , cardiology , anesthesia , hemodynamics
The end‐systolic pressure–volume relationship (ESPVR) is proposed and used as a reliable index of left ventricular (LV) contractility despite the fact that its afterload independence has been challenged. Furthermore, the physiological relevance of its volume‐axis intercept, V 0 , remains unclear. Systemic haemodynamics and pressure–volume loops obtained by inferior vena cava occlusion were recorded in 21 rats anaesthetized by isoflurane inhalation and instrumented with a conductance pressure–volume catheter in response to incremental i.v . doses of adrenaline, dobutamine, phenylephrine, metoprolol, papaverine and isoflurane inhalation. In conditions with large variations (±100%) of both inotropy and afterload, infusion of negative inotropic drugs was associated with a dose‐dependent rightward shift of ESPVR accompanied by a decrease in its slope (end‐systolic elastance, E es ), whereas positive inotropic agents produced an isolated decrease in V 0 . With the predominant vasoactive drugs, there was a dose‐dependent change in E es without major horizontal shifts, demonstrating that this slope mainly represents LV afterload rather than inotropy. When contractility was altered, V 0 was negatively correlated to the preload‐adjusted contractility index, PAd P /d t max , demonstrating that a reduced V 0 provides a good reflection of increased LV contractility. From these results, we computed a logarithmically adjusted E es / V 0 ratio, which resulted in reasonably strong concordance with PAd P /d t max , including all the investigated drugs and dosages [ n = 288; bias, 0.8 ± 16.2% (SD)]. Concordance with E es (bias, 7.2 ± 58.7%) or V 0 (bias, −0.6 ± 33.4%), used alone or with other commonly used contractility indices, was far less significant. In contrast to E es , V 0 provides a relatively good LV contractility index because it is much less sensitive to afterload.