New Index for Oxygen Cost of Contractility from Curved End-Systolic Pressure-Volume Relations in Cross-Circulated Rat Hearts.

Abstract

Recently, we have consistently observed curved endsystolic pressure-volume relations (ESPVRs) of the left ventricle (LV) in rat blood-perfused [1][2][3] and crystalloid-perfused whole heart preparations [4] and in situ ejecting rat hearts [5,6], like those of the puppy LV [7] and adult canine LV in supernormal contractility [8,9]. These studies suggest more generality of the curvilinear than linear ESPVR in different animal species. Despite this curvilinearity, we have obtained a linear myocardial oxygen consumption per Japanese Journal of Physiology, 49, 513-520, 1999 Key words: excitation-contraction coupling, oxygen consumption, E max (end-systolic pressure-volume ratio), systolic pressure-volume area (PVA). Abstract:We have already reported the linear oxygen consumption per beat (VO 2 )-systolic pressure-volume area (PVA) relation from the curved left ventricular (LV) end-systolic pressure-volume relation (ESPVR) in the cross-circulated rat heart. The VO 2 intercept (PVA-independent VO 2 ) is primarily composed of VO 2 for Ca 2ϩ handling in excitation-contraction (E-C) coupling and basal metabolism. The aim of the present study was to obtain the oxygen cost of LV contractility that indicates VO 2 for Ca 2ϩ handling in E-C coupling per unit LV contractility change in the rat heart. Oxygen cost of LV contractility is obtainable as a slope of a linear relation between PVA-independent VO 2 and LV contractility. We obtained a composite VO 2 -PVA relation line at a mid-range LV volume (mLVV) under gradually enhanced LV contractility by stepwise increased Ca 2ϩ infusion and thus the gradually increased PVA-independent VO 2 values. As a LV contractility index, we could not use E max (ESP-V ratio; ESP/ESV) for the linear ESPVR because of the curved ESPVR in the rat LV. A PVA at a mLVV (PVA mLVV ) has been proposed as a good index for assessing rat LV mechanoenergetics. Since the experimentally obtained PVA mLVV was not triangular due to the curved ESPVR, we propose an equivalent ESP-V ratio at a mLVV, (eESP/ ESV) mLVV , as a LV contractility index. This index was calculated as an ESP-V ratio of the specific virtual triangular PVA mLVV that is energetically equivalent to the real PVA mLVV . The present approach enabled us to obtain a linear relation between PVA-independent VO 2 and (eESP/ ESV) mLVV and the oxygen cost of LV contractility as the slope of this relation.

Mechanical work and energetic analysis of eccentric cardiac remodeling in a volume overload heart failure in rats

“…Our recently proposed index for LV contractility (i.e., equivalent maximal elastance [eE max]) was calculated from ESP-volume ratio of the specific virtual triangular area, which is energetically equivalent to PVA mLVV as previously described (17,20).…”

“…The PVAindependent V O2 is composed of V O2 in excitation-contraction (E-C) coupling (18) and basal metabolism (11,17). The RV was kept collapsed (and therefore unloaded) by continuous hydrostatic drainage of the coronary venous return so that the RV PVA and hence PVA-dependent V O2 were assumed to be negligible (19,20). The RV component of total V O2, which is considered constant irrespective of LV volume, was calculated by multiplying biventricular V O2 under unloaded LV volume with the ratio of the RV weight divided by the sum of the RV and LV weight.…”

“…However, the cardiac mechanoenergetics studies have not yet been well conducted. We have established a method to analyze specifically the LV mechanical work and energetics in an excised, blood-perfused whole heart preparation with a cross-circulation method (7,14,17,19,20,24) and analyzed LV mechanoenergetics in a PO heart failure model.In the present study, we focused on the investigation of the mechanical work and energetics in a VO heart failure model with an arteriovenous (AV) shunt in rats. …”

Left ventricular function of isoproterenol-induced hypertrophied rat hearts perfused with blood: mechanical work and energetics

“…However, the cardiac mechanoenergetic studies have not yet been well conducted. We have established a method to analyze specifically LV mechanical work and energetics in an excised, blood-perfused whole heart preparation with a cross-circulation method (29,(32)(33)(34)(35). In the present study, we focused on the investigation of LV mechanical work and energetics in a isoproterenol-induced rat cardiac hypertrophy model.…”

“…V0 was then finally determined as the volume-axis intercept of the best-fit endsystolic pressure (ESP)-volume relationship (ESPVR) in each vol-run. We obtained the best-fit ESPVR and end-diastolic pressure-volume relationship (EDPVR) from five to six different pressure (P)-volume (V) data with the two different exponential functions by means of the least-squares method (Delta-Graph; DeltaPoint, Monterey, CA) on a personal computer (6,7,32,33). Correlation coefficients of the best-fit ESPVRs and EDPVRs were higher than 0.91.…”