he force of the right ventricle in systole is used to push the blood forward into the pulmonary artery (PA) and some part of the force is used to distend the pulmonary vascular tree. When the resistance of pulmonary circulation increases, the PA becomes more distended and less distensible. Some studies of PA compliance have suggested that PA distensibility decreases with rising pulmonary arterial pressure. 1,2 While PA distensibility in patients with pulmonary hypertension (PH) can be investigated non-invasively by magnetic resonance imaging, [3][4][5] this modality is expensive and time-consuming, and it cannot be performed at a patient bedside. Therefore, based on the premise that there is a difference in PA elasticity in acute pulmonary embolism (PE) and chronic PH, we designed this study to find out if non-invasive echocardiography could be used to compare PA distensibility in normal subjects, and subjects with PH and PE. As echocardiographers were often bewildered by echocardiographic signs of right ventricular (RV) pressure overload, which could be disclosed in both PE and PH, we focused and tried to differentiate patients with echocardiographic signs of RV pressure overload by using main PA distensibility. Methods Study PopulationAfter the study protocol was approved by our institutional review board, we enrolled 45 patients (PH group) with echocardiographic signs of PH, defined as a pulmonary arterial systolic pressure of >50 mmHg, evidence of RV dilatation or dysfunction, flattening of the interventricular septum and no filling defect of pulmonary vessels as confirmed by multidetector-row computed tomography. Patients also had cardiopulmonary distress for more than 6 months. The diagnoses of PH patients are listed in Table 1. Another 45 patients with RV dysfunction and flattening of the interventricular septum, which was detected by echocardiography, Circ J 2008; 72: 1454 -1459 (Received March 3, 2008 revised manuscript received April 30, 2008; accepted May 7, 2008 Main Pulmonary Arterial Distensibility Different Presentation Between Chronic Pulmonary Hypertension and Acute Pulmonary EmbolismDen-Ko Wu, MD*; Shih-Hung Hsiao, MD* , **; Shih-Kai Lin, MD*; Chiu-Yen Lee, MD*; Shu-Hsin Yang, MD*; Shu-Mei Chang, MD*; Kuan-Rau Chiou, MD* , ** Background The main pulmonary arterial (PA) distensibility in patients with pulmonary hypertension (PH) and pulmonary embolism (PE) is uncertain. Methods and ResultsWe enrolled 45 patients with echocardiographic signs of PH and without imaging evidence of PE, and another 45 who were found by multidetector-row computed tomography to have PE. Fifty normal patients served as a control group. The PA distensibility was calculated from the change in main PA diameter between diastole and systole, as the maximal systolic diameter minus the minimal diastolic diameter divided by the minimal diastolic diameter. The PA distensibility is lowest in PH (6.0±2.7%), followed by PE (12.9±3.4%) and then the normal controls (25.9±5.7%). Statistical analysis of data obtained from patients ...