FIG 4. Diagram illustrates the physiologic venous stenosis at the thoracic inlet.

A, The left brachiocephalic vein (Bv) is compressed between the aortic arch (Ao) and the sternum (St) during regular breathing (arrowheads).

B, The compression is relieved by full inspiration (arrowheads), because the distance between the aorta and sternum increases due to the elevation of anterior chest wall (arrows). E indicates esophagus; Sv, superior vena cava; T, trachea; V, vertebra