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THE ORIGIN OF THE ANTI-G SUIT - A LINK BETWEEN CLINICAL SURGERY AND AVIATION MEDICINE.
Wilfrid H. Brook RFD, MB, BS(Melb), MS(Mon), FRCSEd, FICA
[presented at] Aerospace Medical Association,
The antigravity suit (anti-G suit) is used in military aviation to apply external pressure to the abdomen and lower limbs. This reduces the pooling of blood in the veins and increases the systemic arterial pressure when a pilot is subjected to several times the force of gravity in a head-to-feet direction during a high speed manoeuvre. This helps to prevent the loss of consciousness which results when the blood pressure to the brain falls to a critical level (1).
In 1903, the year that the Wright brothers first demonstrated powered flight at Kitty Hawk, an American surgeon and a founder of the Cleveland Clinic, published a book titled "Blood-pressure in Surgery". George Crile reported that bandaging the extremities of experimental animals raised their blood pressure, and that compression of the abdomen raised it further. He also found that animals subjected to haemorrhage had immediate haemodynamic improvement when placed in a pressurised chamber and still breathing air at atmospheric pressure, but they died of cardiac congestion (2). To control the externally applied pressure more exactly, he developed a rubber suit which could be inflated by means of a bicycle pump and vary the blood pressure within a range from 25 to 60 mm Hg. The suit consisted of a number of rubber bags which covered the limbs and abdomen and which could be laced together (3). Crile initially used the suit in patients requiring operation in the sitting position (2, 4), but also described how the suit controlled the blood pressure of a train engineer injured in a wreck and who had his left arm amputated (3). Crile eventually concluded that the suit was "cumbersome and uncomfortable" and was impracticable, and he turned his attention to saline infusions for the treatment of shock (3). As the treatment of haemorrhage with fluid and blood became possible Crile's suit was forgotton. Thus the concept of what later became known as the anti-G suit had its origin in clinical surgery as a method of maintaining blood pressure.
With the advent of aviation there were situations in which it was difficult for a pilot to maintain blood pressure when subjected to increasing forces of gravity during turns and this could lead to unconsciousness. By the time the Schneider trophy for the highest speed by a seaplane was permanently secured for Great Britain in 1931 "blacking out" or visual loss had become a problem in closed-circuit racing of high-speed aircraft. The aircraft designed for the Schneider trophy races developed acceleration of 4 to 6 G in turns around the course markers. (5)
Thus by 1931 "blacking out" was a problem, and in 1932 the United States Navy began its initial studies on anti-blackout devices. Lieutenant Commander, later Captain, J.R. Poppen designed a pneumatic abdominal belt which the pilot inflated with a hand bulb prior to anticipated exposure of force. The belt was designed to overcome the pooling of blood believed to occur in the splanchnic vessels in the abdomen (6). The experimental work, in collaboration with Dr. Cecil Drinker of Harvard, had been done on experimental animals exposed to high G forces in aircraft. It was found that abdominal restraint diminished blood pressure effects when the G force ws applied along a vertical axis of the body. The belt was eventually flight-tested by the Navy in June 1941, and the test pilots reported moderate but not wholly adequate protection (7).
A link between Poppen and Crile occurred in 1941, when Crile was in an aircraft that flew into a tornado which caused the plane to crash after producing unconsciousness in its occupants. In his autobiography Crile wrote "After the experience of everyone in the plane it seems clear to me that the cause of the blackout in aviation must be the failure of the blood to return to the brain and the heart because of the rapid ascent of the plane."
He went on to say "So many times I have seen an unconscious patient restored to consciousness by being placed in the head-down position that the blackout seems to me to be just one more phase of the problem that I have been trying to solve for so long and which I solved years ago theoretically if not practically by the device of the pneumatic suit which provided artificial peripheral resistance, giving control over the blood pressure within a range from 25 to 60 mm mercury. This suit enveloped the body up to the chest. Were an aviator encased in this suit and the pneumatic pressure established, the suit in itself would prevent pooling of the blood in the large vessels in the abdomen and extremities and would maintain the conscious state. I believe that an aviator thus equipped would be protected against the failure of the blood to return to the heart and hence would have protection against blackout." So George Crile understood the principle of the anti-G suit.
Crile then corresponded with Dr. Eugene F. Du Bois who was working on problems with aviation and with whom he had already been in contact concerning his pneumatic suit as he knew the idea could be applied to dive bombing to prevent blackout. Soon he was requested to send a description of the pneumatic suit with a photograph to Captain John Poppen (8).
Prior to this, in November 1940, J.F. Fulton, an American physiologist, suggested that pressurised leggings might increase protection on the basis that the lower limbs contained a large reservoir of blood when subjected to acceleration. Accordingly leggings were developed and connected by a tube to the abdominal belt so that the three-piece assembly was inflated from a common source. No centrifuges were available to test it, but it was flight-tested by Wing Commander W.K. Stewart of the RAF Institute of Aviation Medicine at Farnborough, and one of the leggings exploded in flight on the first test. It was evident that the covering fabric was inadequate, and since the assembly was awkward to put on it was suggested (largely by Mr. Fred Moller, an experienced pilot with more than 3,000 hours to his credit) that the pneumatic equipment for the legs, abdomen and arms (for sleeves had now been suggested) be built into a single compact flying-suit (7).
The development of the anti-G suit was not only carried out in the United States and England, but also in Canada and Australia. Between 2 June and 5 June 1940 a water-filled Canadian suit designed by Dr. Wilbur Franks was successfully tested in a Spitfire (9). On 21 November 1941 an Australian gas-filled suit, initially filled with carbon dioxide and later air (10), was successfully tested by the designer, Professor Frank Cotton, in a centrifuge at Sydney University (11).
In conclusion the principle of an air-inflated suit to maintain blood pressure was described by a surgeon in 1903 and who 38 years later was made an honorary Consultant to the United States Navy. According to an account of the history of the Cleveland Clinic (12) George Crile produced the first G suit for military use. However his pneumatic suit was designed long before blackout became a problem to aviators, and the request that he send a description of his pneumatic suit to Poppen came one year after Fulton suggested pressurised leggings could be added to Poppen's abdominal belt. But the fact remains that the principle of an air inflated suit to maintain blood pressure was described by George Crile the same year that the Wright brothers took to the air in their first demonstration of powered flight.
Copyright © 2004, Dr. Wilfrid H. Brook
Posted with permission from the author.
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