New index for oxygen cost of contractility from curved end-systolic pressure-volume relations in cross-circulated rat hearts.
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(2+) 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(2+) 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(2+) 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.
Tsuji
T
T
Department of Surgery III, Nara Medical University, Kashihara, 634-8521, Japan.
Ohga
Y
Y
Yoshikawa
Y
Y
Sakata
S
S
Kohzuki
H
H
Misawa
H
H
Abe
T
T
Tabayashi
N
N
Kobayashi
S
S
Kitamura
S
S
Taniguchi
S
S
Suga
H
H
Takaki
M
M
D000818:Animals; D001794:Blood Pressure; D002306:Cardiac Volume; D006321:Heart / Q000502:physiology*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D010100:Oxygen / Q000502:physiology*; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar
D010100:Oxygen