Pressure–volume analysis

In vivo pressure–volume analysis was performed in mice 5 wk after metformin/vehicle treatment (6 wk after TAC) using a SciSense Advantage Admittance Derived Volume Measurement System and 1.2F catheters with 4.5-mm electrode spacing (SciSense). Mice were anesthetized and ventilated with 1% isoflurane using an SAR-1000 Ventilator (CWE Inc.), and body was temperature maintained at 37°C using a MouseMonitor S platform (Indus Instruments). Mice were secured, and the abdomen was opened below the sternum. The apex of the LV was punctured using a 28-gauge needle, and the catheter was advanced into the LV. The inferior vena cava was located and occluded during a sigh (pause) in ventilation to acquire load-independent indexes. Data acquisition and analysis was performed in LabScribe2 (iWorx). Pressure–volume data were analyzed using a monoexponential fit (P = Ae^βV + c) with the exponent (β) reported as the stiffness (Burkhoff et al., 2005).