Figure 1
Schematic illustration of experimental setting for the excised blood-perfused rat heart (a) and framework of end-systolic pressure–volume relationship (ESPVR)–VO2–pressure–volume area (PVA) (b,c). (a) We used three rats in each experiment. The largest one was used as blood supplier. The middle-size one was used as metabolic supporter for the excised heart. The smallest one was used as heart donor in excised cross-circulation rat heart preparation. The perfusion pressure of the excised hearts was maintained at 100 mmHg with controlled blood pressure of the metabolic supporter rats. Total coronary blood flow (CBF) was continuously measured with an ultrasonic flowmeter placed in the middle of the coronary venous drainage tubing from the RV. The coronary arteriovenous O2 content difference (AVO2D) was continuously measured by passing all arterial and venous cross-circulation blood through the two cuvettes of a custom-made AVO2D analyzer. The myocardial temperature was changed from 37 °C to 32 °C or 42 °C with inline-type temperature controller system for pre-incubation 30 min before data sampling. (b) LV ESPVR and end-diastolic pressure–volume relationship (EDPVR) at midrange LV volume (mLVV, a half value between the minimum and maximum water volume infused into the balloon). The minimal volume loading LV volume (V0) was also determined as the volume-axis intercept of the best-fit ESPVR. The PVA was computed at each LV volume as the area between the ESPVR and the EDPVR and between the V0 and the given chamber volume (balloon material volume + intra-balloon water volume). The value of V0, mLVV, and PVA were normalized by LV mass to 1 g. A striped area denoted PVA at a mLVV (PVAmLVV) (ESPmLVV: observed end-systolic pressure at a mLVV). (c) Myocardial O2 consumption per beat (VO2)–PVA relationship. Myocardial VO2 was obtained as the product of the CBF and coronary AVO2D. The VO2–PVA relation was linear in the rat LV. Its slope represents the O2 cost of PVA (1/contractile efficiency), and its VO2 intercept represents PVA-independent VO2. The PVA-independent VO2 is composed of O2 consumption for Ca2+ handling in E-C coupling and for basal metabolism.
