Relevance of the volume-axis intercept,V₀, compared with the slope of end-systolic pressure-volume relationship in response to large variations in inotropy and afterload in rats

Abstract

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, PAdP/dt 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 PAdP/dt 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. The pressure-volume (PV) loops are used to describe the active and passive mechanical properties of the heart. In particular, the systolic function of the ventricle is analysed by using the end-systolic pressure-volume relationship (ESPVR). The ESPVR is described by a linear slope, the end-systolic elastance (E es ; approximated by maximal elastance, E max ), and by a volume-axis intercept (V 0 ). Suga et al. (1973Suga et al. ( , 1974 showed in the isolated canine heart that E es was load independent, but sensitive to inotropic interventions. This measure of left ventricular myocardial contractility was also applied in conscious dogs (Sagawa et al. 1977;Sodums et al. 1984) and in man (Grossman et al. 1977;Mehmel et al. 1981;Borow et al. 1982).However, these classic notions were later questioned; indeed, the ESPVR has been shown to be afterload dependent (Burkhoff et al. 1993) and, when analysed over wide ranges of contractile states, it was shown to be curvilinear (Burkhoff et al. 1987;Sato et al. 1998). Moreover, logarithmic regression of the ESPVR is superior to linear in estimating the volume-axis intercept (Claessens et al. 2006). Finally, not only the slope of ...

Effects of Cardiopulmonary Exercise Rehabilitation on Left Ventricular Mechanical Efficiency and Ventricular‐Arterial Coupling in Patients With Systolic Heart Failure

“…This fact may be pointing to one of the limitations of the VAC concept, which does not have V 0 data in it. Any change in E es should always be interpreted with the change in V 0 , which has been claimed to be superior and less load dependent than E es for assessment of ventricular contractility 34. Owing to the fact that E es /E a ratio loses pressure data and only contains volume data (stroke volume/end‐systolic volume−V 0 ), it is a corollary that LVEF improves with a decrease in V 0 without any change in E es when stroke volume is kept constant.…”

Perspective of Dimensional Analysis in Medical Science

“…This implies that it is possible to analyze a hypothetical curve E max (V ), which intersects the V axis at point V d . The physical meaning of V d is not completely understood (Blaudszun & Morel, 2011). In the heart model designed in Stergiopulos et al (1996), heart activity is parametrized by six parameters.…”

Ventriculo-arterial Decoupling in Acutely Altered Hemodynamic States

“…1) and is determined for the intrinsic contractility of the heart. Th e steeper the slope, the greater the contractility [16]. Ees (mm Hg/ml) is a usef ul, load independent index of myocardial contractility and LV inotropic effi ciency (end-systolic LV stiff ness) [17].…”