It has, therefore, become the screening tool of choice. However, it should be noted that a proportion of cirrhotic patients have intrapulmonary vasodilation detected at echocardiography without gas exchange abnormalities, and in general these patients do not appear to develop hypoxemia

over time.[15, 56] In bubble contrast echocardiography, a sample of liquid (normally saline) is vigorously shaken to produce microbubbles, and then injected into an arm vein while the cardiac chambers are visualized via a transthoracic approach. Normally, BGB324 cell line these bubbles, which are > 25 μm in diameter, are trapped in the alveolar capillary bed, where the vessels have a diameter of 5–8 μm. Therefore, their appearance in the left atrium after intravenous injection suggests that pulmonary BVD-523 vasodilation has allowed them to traverse the capillary bed, reaching the left side of the heart. A positive study can of course also occur due to the passage of bubbles through a cardiac defect, but in this case the bubbles appear in the left atrium much sooner (within three cycles) after their first appearance in the right atrium. In practice, an intracardiac shunt cannot be definitively excluded in a small proportion of patients with positive studies, and this may require further cardiac investigations. MAA perfusion lung scan is performed by peripheral venous injection of MAA particles that

have been radio-labeled with technetium-99 m, followed MCE by whole body scanning to estimate the extrapulmonary shunt fraction. These radio-labeled particles have a diameter

of 10–90 μm and are removed in the normal pulmonary circulation. Thus, the detection of a significant amount of radiation in the brain or kidneys suggests intrapulmonary vasodilation or intracardiac shunting. MAA scanning appears to be highly specific but less sensitive than bubble contrast echo for detecting intrapulmonary dilatation consistent with HPS, and may fail to detect the presence of intrapulmonary vasodilation in the absence of hypoxia.[15] However, its high specificity makes it useful in diagnosing HPS in patients with coexisting lung disease,[15] and it has the advantage of being quantitative. Chest X-ray may be normal or may show increased vascular markings in the lower zones. High resolution computerized tomography can be helpful in selected patients to exclude intrinsic lung disease, but the absence of vascular abnormalities does not preclude the diagnosis of HPS. A reduced carbon monoxide diffusing capacity is frequently seen in cirrhotic patients and is almost universal in HPS,[10, 12] possibly reflecting diffusion limitation at the alveolus. In the absence of intrinsic lung disease, other pulmonary function tests are normal. Pulmonary angiography can be normal in HPS and is rarely required.