Echocardiography Assessment and Direct Right Ventricle Blood Pressure Measurement

The rats were anesthetized using 5% isoflurane dissolved in 100% oxygen. After the onset of anesthesia, the concentration of isoflurane was decreased to 2.5%, the experimental animals were placed in a decubitus position, and the chest and upper part of the abdomen were shaved. The animals were connected to a Philips iE33 ultrasonograph (Philips Healthcare, Andover, USA) to record ECG from the II lead. Then, the rat was placed on the left side, and a four-chamber view was recorded from the apical point of view using a Philips (Philips Healthcare, Andover, USA) S12-4 sector array transducer. Right ventricular (RV) end-diastolic area (RV-EDA) and RV end-systolic area (RV-ESA) were recorded. ECG was used to determine the exact time of RV systole and diastole. Furthermore, RV-EDA and RV-ESA were used to calculate RV fractional area change (RVFAC). The rat was again placed in a decubitus position, and functional parameters of the left ventricle were recorded at the papillary muscle level using a Philips (Philips Healthcare, Andover, USA) linear L15-7io transducer.

After the echocardiographic assessment of ventricular anatomy and functioning, invasive direct right ventricular pressure measurement was performed. The anesthetized rat was intubated using a 16-G intravenous catheter and mechanically ventilated with 2% isoflurane dissolved in 100% oxygen at a tidal volume of 1.5 ml/100 g. The abdominal cavity was opened, and the diaphragm was incised to expose the pleural cavity. The ribs on both sides of the chest were cut to access the heart. An 18-G needle was connected to a pressure transducer (AD Instruments, Sidney, Australia) and inserted into the cavity of the right ventricle through the apex of the heart. The right ventricular pressure was measured until a stable pressure reading was obtained.