Perfusion Modes
During Langendorf mode (LM), oxygenated perfusate is pumped retrograde by a centrifugal pump (CP) into the aorta at a constant pressure of 50 mmHg to close the aortic valve and allow perfusate flow into the coronary vessels. The perfusate drains into the coronary sinus and through the RV it is ejected back to the reservoir via a cannula into the pulmonary artery.13
In this experiment the donor heart was mounted on the ESHP system following 1h of cold-storage. Anterograde flow through the LA was commenced for de-airing of the left cardiac chambers. Once completed, all hearts were first perfused in LM. Over the course of 30 minutes, hearts were rewarmed to 37℃. Hearts that fibrillated were defibrillated as required. Perfusion was kept steady at these settings for another 30 min. The metabolic assessment of the donor heart was performed hourly in LM. For the functional assessment, the hearts were transitioned to SAM as described previously and the LA loaded with an inflow corresponding to a cardiac index of 1.8 L/min/m2 based on donor weight. The right atrium was loaded with an inflow such that the sum of the inflow and coronary flow corresponded to a cardiac index of 1.8 L/min/m2 based on donor weight. The centrifugal pump and left atrial resistance were adjusted such that diastolic pressure was maintained between 25-30 mmHg. Systolic aortic pressure was not controlled. A Windkessel module was added on the aortic line in order to regulate systolic and diastolic aortic pressure. The evaluation process was performed with a standardized systemic resistance of 2 mmHg/cm3 and a standardized arterial compliance of 2 cm3/mmHg. The LV was assessed in SAM at one hour (indicated as SAM1), then switched to LM. After 4.5 hours was assessed in PAM and after one hour of LM (5.5 hours of perfusion) the hearts were switched back into SAM2 to perform the final functional assessment. Figure 1A shows the detailed setup.
Continuous infusions of dobutamine (0.05 mcg/min), nitroglycerin (1mcg/kg/min), and insulin (5 units/h) were maintained throughout the experiment. Fraction of inspired oxygen (FiO2) and gas flow through the oxygenator were titrated to maintain a pH between 7.35 and 7.45, a pO2 between 100 and 300 mmHg, and a pCO2 between 35 and 45 mmHg. Arterial and venous samples were collected at baseline and hourly during ESHP. Electrolyte, lactate and hemoglobin concentrations, pH, pO2, pCO2 and oxygen saturation (SpO2) were measured using a blood gas analyzer (RAPIDPoint® 500 Blood Gas Systems, Siemens). Myocardial lactate metabolism was determined as follows:
Myocardial Lactate Metabolism [mmol/L]=Pulmonary Artery Lactate [mmol/L] - Aortic Lactate [mmol/L]
A positive result indicates production, whereas a negative result indicates extraction. All metabolic parameters were assessed with hearts perfused in LM. The heart was weighed at the beginning and at the end of the perfusion.