Abstract: Objective To study changes in pulmonary surfactant proteins A （SP-A） and B （SP-B） in rat lung tissue after one lung ventilation.Methods Sprague-Dawley rats （n=42） were randomly divided into three groups：one lung ventilation group （group A），two lung ventilation group （group B），and control group （group C）.Groups A and B were further subdivided depending on the ventilation time （A1，A2，A3；B1，B2，B3）.An artificial endotracheal tube was pushed into the right main bronchus in order to perform one lung ventilation.Pathological changes in the lung were examined by light microscopy，and the expression of SP-A and SP-B in lung tissues was detected by Western blot.Result In contrast to group C，groups A and B showed intra-alveolar exudates，hemorrhaging and interstitial edema that was proportional to ventilation duration.The left （unventilated） lung showed more serious damage than the right lung in group A.Levels of SP-A and SP-B were significantly lower in group A than in group C（P＜0.05），and the levels in group A decreased with increasing OLV duration（P＜0.05）. In the left lung，levels of SP-A and SP-B were significantly lower in A1，A2，and A3 than in B1，B2，and B3，respectively（P＜0.05）. In the right lung，there were no significant differences between groups A and B in the expression of SP-A （P＞0.05），nor were there significant differences between A1 and B1 or A2 and B2 in the expression of SP-B （P＞0.05）.However，the levels of SP-B were lower in A3 than in B3 （P＜0.05）.The levels of SP-A and SP-B were lower in the left lung than in the right one in A1，A2，and A3（P＜0.05）.Conclusion OLV causes the levels of SP-A and SP-B in lung tissue to decrease below the levels observed with two lung ventilation of the same duration.This may be a primary cause of the more serious lung injury caused by OLV.

Key words: One lung ventilation, Pulmonary surfactant protein A, Pulmonary surfactant protein B