Echocardiographic Evaluation of the Change on Pulmonary Blood Flow and Cardiac Function During One-lung Ventilation

The investigators used transesophageal echocardiography (TEE) to assess the change of pulmonary blood flow and bi-ventricular function during lung isolation. The investigators hypothesized that changes in pulmonary venous flow with lung isolation may be related the shunt fraction and oxygenation during one lung ventilation (OLV). The investigators also observed the cardiac function during two lung ventilation (TLV) and OLV in supine and lateral position by TEE.