Suspension Trauma

 by Eva D

Something unknown to many people despite its infamous reputation among climbers is a condition known as suspension trauma. When the human body is held motionless in a vertical position for a period of time (feet pointing down), the person will lose consciousness and this will eventually lead to death. This is most common in climbers, builders, skydivers or any profession which involves harnesses. The reason for this is because gravity causes venous pooling to occur: blood collects at the bottom of the legs. Veins carry blood towards the heart with the help of muscle contraction, and valves which prevent the backflow of blood. Arteries, however, carry blood away from the heart and do not require muscle contraction, other than the heart, to function properly. You can now deduce that if someone's calf is suspended and not contracting or exerting force, then not only will arteries carry blood to the lower leg, but said blood will not be able to return to the heart via the veins as there is no muscle contraction to move the blood against gravity, thus causing venous pooling. While a harness causes someone to be in this suspended vertical position, its straps may compress the femoral vein in the thigh, further reducing the amount of blood returning to the heart. Venous pooling can also occur in people who sit for long periods of time as this may compress their veins, increasing stress on the valves which leads to venous incompetence, or valves that don’t work properly (this can be seen in people with swollen, blue/purple lower legs). The reason this specific condition leads to unconsciousness is due to the fact that a lower volume of blood is reaching the brain - venous pooling alone can result in a 20% loss in circulating volume. 

There are various factors that can worsen suspension trauma, the most significant being dehydration. The heart has to work much harder to pump high viscosity blood as there is more resistance in blood vessels and a higher blood pressure. The body, however, does not give in this easily and can use compensatory mechanisms to keep you conscious for as long as possible. In order to combat dehydration, a hormone called vasopressin is released to help your kidneys retain water. This also binds to receptors on vascular smooth muscle cells and induces the release of Ca2+ ions from the sarcoplasmic reticulum present in muscle cells. These ions cause vascular smooth muscles to contract which narrows blood vessels leading to less important areas of the body such as arms and legs and promotes blood flow to vital organs. This is called peripheral vasoconstriction (‘peripheral’ meaning an outer area ‘vasoconstriction’ meaning the narrowing of blood vessels). These compensatory mechanisms can only last a short period of time as the build up of venous pooling will continue to decrease the circulating blood volume. As the circulating blood volume is lower in a dehydrated person, they will still experience suspension trauma at a faster rate than a hydrated person despite their compensatory mechanisms. The speed at which suspension trauma can occur varies between roughly 5-30 minutes. Although this appears like a sufficient amount of time to change body positions in a harness - a climber who may be unconscious as part of their circumstance will be unable to do so and therefore more likely to lose brain function (leading to death) at a faster rate.