Autoperfusing Ectothermic Heart-Lung Preservation System

Abstract

A portable heart-lung preservation system was developed to enable distant organ procurement. In 8 dogs, a functioning heart-lung system was isolated, cannulated in situ, removed en bloc, and placed into a Plasmalyte-filled, temperature-controlled (15-38°C) chamber. The perfusion circuit consisted of an adjustable-height, autologous-blood reservoir. The heart ejected through the aortic cannula with venous return (VR) into the superior vena cava. Respiration was maintained with a positive pressure ventilator. Intramyocardial tissue pressure (IMP), tissue pH, right atrial (RAP), aortic pressure (AOP), and cardiac output (CO) were monitored. Autoperfusion at normothermia and CO of 50 mL/min/kg resulted in early (3 h) deterioration of pulmonary function with progressive interstitial lung edema. Pulmonary dysfunction always preceded changes in regional myocardial contractile viability (peak IMP and d(IMP)/dt) and global function (CO, AOP). When tissue pH was regulated ectothermically (as in cold-blooded animals) (ΔpH/°C = -0.015) the heart maintained a stable pumping mode (>6 h) at myocardial temperatures of 17-28°C, pH = 7.70-7.55, and heart rate of 25-50 bpm, respectively. The results indicate that a viable (>6 h) autoperfused, working heart-lung system can be achieved by reducing the circulating blood flow to 30-50% of normal CO. More significantly, ectothermic alpha-stat modulation of perfusate pH and pCO₂ allows a substantial reduction in organ temperature and metabolic demand without endangering induction of fibrillation and ultimate allograft failure.