Text Box: EXPERIMENTAL STUDY OF THE PULMONARY EFFECTS OF L-ARGININE DURING DEEP HYPOTHERMIC CARDIOPULMONARY BYPASS YANG YM, SU ZK, ZHANG HB, CHEN E, WANG SM Department of Cardio-thoracic Surgery, Shanghai Children’s Medical Center, China Objective: After establishing the deep hypothermic cardiopulmonary bypass (DHCPB) model on piglets as in open-heart surgery, the influence of different dosages of L-arginine on piglet lungs were studied. Measurements of lung compliance, airway resistance, artery-alveolar O2 pressure ratio,nitric oxide synthesizing rate and lung water content were performed to find out whether L-arginine had any protective effects on the lung during DHCPB. Methods: 30 piglets, aged 4-5 weeks and weighing 7-9kg, were randomly divided into 3 levels, i.e. group A (placebo control), group B (20mg/kg/min L-arginine) and group C (40mg/kg/min). Animals were anesthetized and undergone DHCPB according to clinical routine. During DHCPB, L-arginine or placebo dissolved in Ringer’s solution was infused into the lungs through the pulmonary catheter. The measurement of the above-mentioned indices was performed at 3 different times, i.e. before commencement of DHCPB, at the end of DHCPB and 1 hour after cessation of DHCPB. Results: pulmonary vascular resistance index, nitric oxide synthesizing rate, lung water content after DHCPB were significantly higher than that before DHCPB.At the same time pulmonary compliance and artery-alveolar oxygen pressure ratio were significantly lower both in both groups B and C. The above changes were also observed in group A except that nitric oxide synthesizing rate was unchanged. Comparisons among different groups showed that NO synthesizing rate was significantly higher in groups B and C. Pulmonary vascular resistance index was significantly lower in groups B and C. Pulmonary compliance and lung water content were higher, but not significantly, in groups B and C. Airway resistance was not different among the three groups. Conclusions: L-arginine has some protective effects on the lungs during DHCPB. 1857