Flow in the aorta descendens (arrow, yellow contour) and vena azygos (dashed arrow, green contour), images in systole (28-years old healthy male volunteers). Normal breathing (A-B) and Valsalva maneuver (C-D). Lumen of the aorta und vena azygos is compressed during Valsava (C, D), especially reduced in the superior vena cava (white stars). The luminal area and diameter of thoracic vessels is reduced under elevated intra-thoracic pressure. Scan area (localizers) were adapted to Valsalva and normal breathing, because mediastinal and heart structures are moved during variation of the intra-thoracic pressure.