By Dr. Norman Wood

While suspended in a safety harness, the leg straps cause a tourniquet effect on the femoral vein and pressure on the femoral nerve, causing blood to pool in the lower extremities, and considerable discomfort and pain.  The venous return from the legs has very little pressure behind it, approximately one-fifth of the arterial pressure going into the legs. During ambulation, the normal venous pressure in the feet of 25 mm Hg can be increased to 90 mm Hg in just a few minutes due to gravitational pull on the blood and immobility. 

To assist the body in the movement of blood against gravity, the venous return from the legs has one-way valves to help the transfer of blood back to the heart. To provide the pressure needed to overcome the gravitational pull on the blood, active leg muscle contractions must be used.  As the leg muscles contract, pressure is exerted on the veins in the legs forcing the blood through the one-way valves and back to the heart.  

Unfortunately, while suspended in a harness, the “muscle pumps” of the legs may be inadequate to overcome the compressive forces placed on the femoral veins by the leg straps and blood pooling occurs. Even with active leg movements, which can prolong the onset of presyncope symptoms, they ultimately may be ineffective against the rapidly progressing chain of events that cause increasing immobility and unconsciousness.    

There are many reasons why a suspended person would become immobile; a lack of understanding of Suspension Trauma, injury, confusion, physical and emotional exhaustion, pain, hypoglycemia, muscle failure due to hypoxia and aesthesia of the legs, or the Suspension Trauma Cascade has progressed to the point of unconsciousness. The longer the suspension, the less mobile a person will become and the Suspension Trauma Cascade of events will begin to proceed at an ever-progressive rate.     

The average human body contains ten pints of blood with two pints normally in the legs at any one time.  As soon as a person is suspended in a rear-attached harness, those two pints of blood are trapped in the legs and the body has a decrease of 20% of its total circulating blood volume, and Class II Hypovolemic Shock is present. The heart is powerful enough to push the blood past the leg straps via the arteries and as long as the heart continues to beat, more blood will be pushed into the legs where it will be trapped.  

Vasovagal Event (Fainting)

The lower extremities can hold 60% (six pints) of a body’s total blood volume.  As soon as the heart has pumped over 40% (four pints) of blood into the legs, the victim is now in Class IV Hypovolemic Shock, the most severe level of Hypovolemic Shock with impending death if no immediate medical care is rendered.  There is no Class V.    

This is the same as cutting both wrists and bleeding out half of the body’s blood. Blood pressure and oxygen levels drop to a critical point where it causes unconsciousness and then death. If the body is placed in a horizontal position, survival is possible; however, being suspended by a harness in a vertical position, there is little chance of survival without immediate suspension relief.

A Vasovagal syncopal event, fainting, while suspended in a vertical posture can end in the same catastrophic result. The Autonomic Nervous System (ANS) controls our “Fight or Flight” responses as well as our “Normal Relaxation State”.  In an emergency, similar to having a harness fall stop, the sympathetic or “Fight or Flight” component of the ANS quickly prepares us to physically respond by increasing the heart rate, breathing, and blood pressure through catecholamine release and blood vessel constriction.

This sympathetic control will remain dominant in an emergency unless reduced by an increasing parasympathetic tone.  The parasympathetic or “Normal Relaxation State” component of the ANS creates the opposite effect on the body by decreasing the heart rate and blood pressure. The 10th Cranial Nerve, the Vagus Nerve is part of the parasympathetic ANS.  

The Vagus Nerve can be stimulated by pain, emotional stress, and hypovolemia. While suspended in a harness the body can be experiencing all three stimulants and the longer the suspension, the more intense the vagal tone will become.  Contributing to this vasovagal event is the Bezold-Jarisch Reflex which is initiated when ischemic hypoperfusion or hypovolemia is sensed by chemoreceptors and mechanoreceptors in the left ventricle of the heart. This reflex causes a marked increase in vagal tone causing immediate bradycardia and dilatation of blood vessels by decreasing the sympathetic input.     

When the vagal tone becomes significant enough, a vasovagal syncopal event will occur due to the rapidly decreasing heart rate, blood pressure, and cerebral perfusion. This can take a minute or two where the victim feels the symptoms of presyncope, or it can be instantaneous as in a person fainting over the sight of blood or being stuck by a needle. A victim will never know how soon this event will occur, but it will be very rapid. 

Elements of the Suspension Trauma Cascade can present so suddenly that the suspended victim may have little opportunity to respond in an effective manner.  One of the earliest symptoms of Suspension Trauma is cognitive impairment or confusion which makes the suspended victim much less likely to be able to assist in their own self-rescue.        

As soon as the Suspension Trauma Cascade progresses to the victim’s limits of physical or emotional tolerance, unconsciousness will occur by hypovolemic shock, vasovagal event, or both. During unconsciousness, the respiratory rate will slow, oxygenation of the brain and heart will diminish, thus causing a greater drop in respiration and blood pressure which causes a further drop in oxygenation and the cascade spirals downward.  There will be permanent brain damage in a few minutes. The heart will stop shortly after that when it sustains a global myocardial infarction, a “massive heart attack” from the lack of oxygen and death occurs. All of this can happen in “less than 30 minutes”.

Blood Clot Formation Beginning in Pooled Blood after 10 minutes
Well-Formed Blood Clot in Pooled Blood after 20 minutes
Blood Clot completely formed in Pooled Blood after 30 minutes


Recall that these victims had prolonged suspensions anywhere from 30 minutes to eight hours before being rescued, some of whom had Suspension Relief Straps. All of them were in front-attached harnesses or rope slings.  

The two that died before being rescued may have succumbed to the classic cascade of events associated with Suspension Trauma. Either hypovolemic shock when excessive blood pooling in the legs or a vasovagal syncopal event occurred.  With either, blood pressure and brain oxygenation will drop to a critical level where the victim becomes unconscious and death quickly follows.  

The three victims that died shortly after being rescued may have died of sudden cardiac arrest or pulmonary emboli. This can be caused by hypoxic injury to the myocardium while suspended and by the blood which was once pooled in the legs becoming a toxic sludge which consists of low oxygen levels, blood clots, and high potassium (hyperkalemia). The third and final injection during a Lethal Injection Execution is potassium, it stops the heart.  

While suspended in a harness, the extent of stasis that the blood is exposed to will determine the degree of pathological changes that occur to that collection of blood. If the venous return is only slowed as in a sit harness with increasing immobility, the pathological changes in the pooled blood of the legs will take longer to occur, perhaps hours. If the venous return is stopped or near so as in a rear-attached safety harness, the pathological changes will begin to occur immediately.  

As blood pooling continues in the legs, increasing hypoxia within the stasis blood triggers anaerobic metabolism in the muscle cells.  Lactic acid, a byproduct of anaerobic glycolysis, causes the pooled blood to become increasingly acidotic. During an acidotic state, an ionic shift will occur between the hydrogen ions in the blood and potassium ions in the muscle cells causing the pooled blood to become hyperkalemic. Damaged Red Blood Cells will also release their own potassium.     

As the pooled blood becomes more hypoxic and stagnant, micro blood clot formation will begin very quickly which can lead to Deep Vein Thrombosis (DVTs). When the movement of blood, circulation, is stopped this imitates death to that section of the body. Anyone that has harvested a game or farm animal and then immediately cleaned that animal has observed the clot formation that has already accumulated. This same process of pathological change occurs in the stasis blood of the legs while suspended. Clot formation is easily observed in this instance, what cannot be visually observed is the pathological changes of the chemical composition of the blood to an acidotic state with high potassium and low oxygen content.  

At ten minutes, the pooled stasis blood is already starting to form clots. The scattered dark spots are the micro clot formation and the thickened area is more advanced clot formation. Although troublesome, a person would have a good chance of survival if this blood was allowed to circulate back to the heart and lungs.  At 20 and 30 minutes, these clots are well-formed and are potential killers and if allowed to circulate back to the heart and lungs, death can occur in less than one minute.  

The pathological chemical changes occur at the same time and for the same reasons that clot formation begins and depending on the type of harness suspended in and the length of time of suspension, over half of a person’s total blood volume may become incompatible with life.  Once the tourniquet effect of the leg straps is removed, this blood can rapidly return to the heart, causing it to go into a fatal arrhythmia, and/or clots can be shed to the lungs, either of which can kill a victim very quickly.  

The victims that died shortly after being rescued may have been laid down in a supine position, which is considered the standard of care for trauma victims; however, this can be detrimental if the conscious and alert victim has been suspended for a prolonged period of time. It must be remembered that a suspended person is not a typical trauma victim. They have not fallen to the ground, they have been suspended, a very unique circumstance. On-site, EMS care must be adjusted and is discussed later.    

The final five may have died over the next few days of hypoxic damage sustained by the heart, pulmonary emboli, or acute kidney failure. The kidneys cannot tolerate low blood flow and low oxygen levels caused by blood pooling while hanging suspended in a harness.  Renal tubular necrosis is the kidney “rotting from the inside out” and is caused by hypoperfusion while suspended.  

The kidneys can also be damaged by myoglobin, a large muscle protein released in the blood when muscle cells begin to break down in a low oxygenated state and from leg strap compression injury, a condition called Rhabdomyolysis. These bulky proteins obstruct the fine membranes of the filtration system of the kidneys causing acute kidney failure. 

It can take a day or two before acute kidney failure becomes significant enough to make the victim ill.  A short period of no symptoms may precede the acute onset of kidney failure which can quickly lead to death.  Fifty percent of all acute kidney failure victims die.


It is very clear from all available reports and studies conducted on Suspension Trauma and from the medical knowledge of the pathophysiological effects on the body, a person will never know how much time he will have to survive and even if rescued after being suspended for a prolonged period of time, that victim is still in very grave danger of serious injury or death. Suspension Trauma can be quickly lethal and anyone using a rear-attached full body harness must be aware of the dangers and use all precautions. 

That being said, if you do not wear a full-body harness and fall, your odds of survival may be zero. Even if you survive, you may still sustain catastrophic injuries where any further employment is impossible for the rest of your life. Always wear a full-body harness and use all available safety measures.

Dr. Norman Wood graduated with honors from the West Virginia School of Osteopathic Medicine after 16 years of working in law enforcement for the WV State Police. In 1998, he fell 20 feet from a tree while trimming limbs and sustained injuries that immobilized him for almost 4 months. During his recovery, he began inventing new technology for fall prevention, and he continues his work through the present day. Dr. Wood is the owner of 4 U.S. Patents and several U.S. Patent Pending inventions for safety products that make elevated work and tree stand hunting safer.

Contact Us

"*" indicates required fields

This field is for validation purposes and should be left unchanged.