such怎么理解？

Rarely, there may be passage of air emboli from the right to left heart without an overt right-to-left shunt. This is important because air then enters the systemic arterial circulation where there may be embolism and infarction, particularly of the brain. It is possible to pass a probe through such a foramen ovale in over 25% of the adult population (page 164), but paradoxical embolism does not usually occur because pressure is slightly higher in the left atrium than in the right. However, under many circumstances, such as following pulmonary embolism, right atrial pressure may be elevated to the point that a right-to-left shunt occurs.

极少数情况下，心内无明显的右向左分流时，栓塞的空气从右心进入左心。这一点很重要，因为空气随后进入体循环动脉，可能会在体循环动脉发生栓塞和梗死（特别是大脑）。在超过25%的成年人中，探针可能穿过卵圆孔（第164页），但由于左心房的压力略高于右心房，因此反常性栓塞通常不会发生。然而，在许多情况下（如肺栓塞后），右心房压力可能会升高指引起右向左心内分流的程度。