Influence of Posture on the Parameters of the Unilateral Pulmonary Arterial Occlusion (UPAO) Test

The unilateral pulmonary arterial occlusion (UPAO) test is employed preoperatively to evaluate cardiopulmonary function and determine whether patients can tolerate lung resection. Lung resection is generally performed with the patients in the lateral position. We therefore conducted the UPAO test in both the lateral position and supine position to assess how hemodynamic changes in the acute phase immediately after intraoperative ligation of the pulmonary artery would be predicted by UPAO parameters in both positions. The subjects were 14 lung cancer patients who were scheduled to undergo pneumonectomy or lobectomy between January 1996 and January 1998. They were 10 males and 4 females, and their mean age was 68.7 ± 11.4 years. Mean pulmonary artery pressure (Ppa), mean pulmonary arterial wedge pressure (Ppw), and cardiac output (CO) by the thermodilution method were measured in both the supine and the larteral position to estimate total pulmonary vascular resistance index (TPVRI) and pulmonary vascular resistance index (PVRI). The points selected for making the measurements were the mid-axillary line in the supine position and the spinal midline in the lateral position. Mixed venous blood and arterial blood samples were collected for blood gas analysis. The Ppa values in the supine and the lateral position during UPAO were 18.4 ± 5.7 and 16.6 ± 5.7 mmHg, respectively, TPVRI values were 516 ± 235 and 467 ± 211 dyne・sec・cm^・m^2, respectively, and the mixed venous blood gas values (PvO_2) were 36.8 ± 3.3 and 35.4 ± 3.2 mmHg (p