Why is the lower torso protected in traumatic asphyxia? A new hypothesis.

Traumatic asphyxia secondary to a crush injury of the chest is characterized by craniocervical cyanosis, subconjunctival hemorrhage, and severe vascular engorgement of the head and neck. These signs are believed to be due to high venous pressures causing stasis and capillary rupture. A "fear response" that produces a strong Valsalva maneuver is thought to be necessary for their development. The lower torso seems to be protected, and previously this was thought to be due to its superior system of valves. We present here ultrasonographic evidence that the inferior vena cava is compressed or obliterated during a Valsalva maneuver, and propose that this compression protects the lower torso during traumatic asphyxia.