A STUDY ON OPTIMAL TEMPERATURE FOR ISOLATED LUNG PRESERVATION

Fifty-two heart-lung blocks (grafts) of New Zealand white rabbits were used for determining optimal temperature in lung preservation. Grafts were inflated with room air and preserved by simple surface cooling at arbitrarily determined temperatures for 18 hours. Graft function was assessed by nonrecirculated perfusion with autologous blood. Segmented regression models between functional parameters and preservation temperature (T) were applied for determining optimal temperature. Graft ability was also assessed from the point of view of pulmonary circulation by indocyanine green dilution rate of effluent and histological distribution of carbon particles. Significant segmented regression curves and lines between parameters of effluent oxygen tension (PO2) and wet-dry weight ratio (W/D), and T were obtained as follows: PO2 = 150/(1 + 3208.1[e-1.17T]), p < 0.01; PO2 = -13.8T + 222.6, p < 0.05; W/D = 5.0 + 1.5/(1 + 0.0028[e0.94T]), p < 0.01; W/D = 0.075T + 4.52, p < 0.05. Optimal temperature for lung preservation by topical cooling was calculated as 8-degrees to 9-degrees-C from each intersecting point of regression equations. Analysis of regression curves suggested that the most common hypothermic ischemic injury during preservation by topical cooling is pulmonary vascular obstruction, which might be induced at temperatures lower than the critical temperature of 6-degrees to 7-degrees-C. Indocyanine green dilution rate and histological findings supported the results of graft functional parameters.