Abstract： Objective To investigate whether passive leg raising(PLR)combined with ultrasonic cardiac output monitoring system(USCOM)could be used to predict the hemodynamic response to volume expansion(VE)in patients with spontaneous respiration. Methods The study was performed with prospective, cohort study method. Thirty-three patients with spontaneous breathing activity who were admitted to the intensive care unit(ICU)from October 2009 to April 2010 were included. Measurements of stroke volume(SV)were obtained with transthoracic echocardiography(TTE)and USCOM. Patients were considered to be responders to VE if SVTTE increased≥ 15%. Based on the responsiveness of VE, all the patients were divided into responders and non-responders. The change in SV(△SV)after the experiment and its correlation were observed. Results A total of 36 fluid load tests in 33 patients were evaluated resulting in 24 responders and 12 non-responders. There was no significant difference between two groups in the clinical data and hemodynamics parameters at incipient stage when head side of bed was raised for 45°. After PLR,the △SVTTE and △SVUSCOM in responder group were significantly higher than those in non-responder group [△SVTTE:(21.7±13.2)% vs.(4.8±9.4)%, △SVUSCOM:(23.5±13.0)% vs.(4.6±8.9)%, both P＜0. 01], with positive correlation between △SVTTE and △SVUSCOM(r = 0. 792, P＜0. 01). After VE, the △SVTTE and △SVUSCOM in responder group were significantly higher than those in non-responder group [△SVTTE:(27.3±14.1)% vs.(7.2±8.4)%, △SVUSCOM:(25.4±13.8)% vs.(6.7±8.6)%, both P＜0. 01], with positive correlation between △SVTTE and △SVUSCOM(r= 0. 855, P＜0. 01). The △SVTTE≥ 15%during PLR was predictive of response to VE with a sensitivity of 100. 0%[95% confidence interval (95%CI)85.0 - 100. 0]and a specificity of 83. 3%(95%CI 68.4 - 98. 2). The △SVUSCOM≥15% during PLR was predictive of response to VE with a sensitivity of 83.3%(95%CI 66. 1 - 100. 0)and a specificity of 94.4%(95%CI 83. 9 - 100. 0). There was no difference between the area under the receiver operating characteristic(ROC)curve for PLR-induced △SVTTE and △SVUSCOM(0. 95±0. 04 vs. 0. 93±0. 05, P＞0. 05).Conclusion PLR combined with USCOM can predict the hemodynamic response to VE in spontaneously breathing patients, and the procedure can be used to guide fluid therapy in spontaneously breathing patients.