ROCHESTER, Minnesota — If you have watched "Top Gun: Maverick," you saw a fictional portrayal of fighter pilots performing incredible aerial maneuvers at high G-forces, or the force of gravity. Here is the story about the role Mayo Clinic had helping U.S. pilots reach those heights in World War II.
In 1942, the U.S. government secretly tasked a small group of Mayo Clinic physicians and researchers with developing technology that would help lead the U.S. and its allies to victory a few years later.
Mayo Clinic physician-researchers Walter Boothby, M.D.; W. Randolph Lovelace II, M.D.; and Arthur Bulbulian, D.D.S., had designed an oxygen mask, called the BLB mask (for Boothby-Lovelace-Bulbulian), a few years earlier to solve the problem of airplane passengers experiencing low oxygen levels while flying. Now adjustments were needed to better suit military needs for the war effort.
Dr. Bulbulian quickly began improving the mask for pilots flying jets higher and faster than typical aircraft. The updated BLB mask, now known as the A-14 mask, provided pilots with as much supplemental oxygen as needed, was frost-resistant and had a microphone for radio communication.
As Dr. Bulbulian solved one problem, the U.S. military quickly discovered another. Pilots experienced G-forces so severe it resulted in blackouts. At 2-Gs, pilots feel twice their body weight pushing them against their seats. At 3-Gs, they experience triple their weight, and so on. As the G-force increases, it becomes increasingly difficult for the heart to pump blood to the head, resulting in a lack of oxygen to the brain. To discover how pilots tried to combat this on their own, researchers went right to the source.
"Pilots would consistently say that they would just yell at the top of their lungs as they were about to pull out of their bomb-diving run," says Jan Stepanek, M.D., director of aerospace medicine at Mayo Clinic in Arizona. "When you really yell hard, you create increased pressure in your chest, which results in high blood pressure as long as you're yelling."
The goal of Mayo Clinic researchers Earl Wood M.D., Ph.D., and Charlie Code, M.D., was finding a practical way to keep blood flowing to the brain during gravitational stress, because pilots could only yell for so long. This led to the development of the M-1, or Mayo-1, maneuver. This eventually developed into what is known today as the anti-G straining maneuver, nicknamed "the grunt."
"What it is is a straining maneuver that is designed to primarily increase arterial blood pressure. It consists of voluntary contractions of both legs, calves, thighs, arms and increasing pressure in your abdomen," Dr. Wood said in an interview for the Mayo Heritage film, "Reaching New Heights: Secret Stories of the Mayo Clinic Aero Medical Unit." "When someone knows how to do that, they can increase their blood pressure … if they work at it hard enough."
This maneuver had pilots focus on constricting their bodies and controlling their breathing so blood could flow more easily to their hearts and brains, preventing loss of consciousness under higher G-forces. The anti-G straining maneuver alone couldn't get them to safely fly over 3- and 4-Gs. Still the anti-G straining maneuver is incredibly important for pilots even now: "The maneuver was teachable and trainable, and arguably more important than the G-suit," Dr. Stepanek says.
While the original model of the G-suit had already been developed, improvements made by Dr. Wood, and David Clark, a weaver from Massachusetts, allowed pilots to fly up to a force of 9-Gs. Dr. Wood and Clark took the revolutionary concept of the G-suit, developed in 1941 by a team led by Wilbur Franks, M.D., at the University of Toronto, and devised an inflatable, five-bladder system that could be slipped into a garment. At the same time, the aeromedical team perfected a valve to reliably connect the suit to the plane's air pressure system. While the previous design focused more on the gravitational pull, Dr. Wood's design focused on increasing arterial pressure without needing the pilot's attention or effort.
Testing the suit's design wasn't easy. Researchers and physicians didn't want to test the concept on others because the effects G-forces cause — lack of oxygen to the brain and blood flow to the heart — weren't yet known. So, they tested it on themselves.
The need for testing G-suit designs led Mayo Clinic researchers to build a gigantic human centrifuge in the Medical Sciences Building in Rochester. The centrifuge, designed and built by Dr. Code; E .J. Baldes, M.D.; and Adrien Porter, was the first of its kind in the U.S. A simulated cockpit was attached to the end of a tubular steel structure powered by the remains of a wrecked Chrysler automobile engine. Two 20-ton flywheels provided the momentum and energy to spin the cockpit at high speeds, creating intense G-forces. Using the centrifuge, the Mayo Aeromedical Unit gathered the most complete data ever recorded on the effects of G-forces.
When asked about the unknown damage lack of oxygen causes to the brain, Dr. Wood said in the film he didn't really think about it: "I don't remember having any concern that the repeated blackouts and so on might cause residual damage. We never worried about it very much."
Even with the data, pilots wanted real-world proof that the suits would work before trusting their lives to them. This led the Mayo Clinic Aeromedical team to request a fighter plane — a Douglas Dauntless dive bomber — and a volunteer pilot. To test the inventions, the pilot flew the plane while the researchers sat in the back seat. These real-world experiments, led by Edward Lambert, M.D., Ph.D., proved that the G-suit alone could provide protection up to 7-Gs. When the suit was combined with the anti-G straining maneuver, pilots could function up to forces of 9-Gs. After the tests, the concept of the new G-suit was accepted by the Army and Navy and is sometimes credited as making a difference in winning the war.
Today, the G-suit concept and anti-G straining maneuver created by the team at Mayo Clinic are used by fighter pilots worldwide. To learn more, visit Discovery’s Edge, Mayo Clinic History & Heritage website and the Department of Defense Medical Research Office webpage.
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