PANAMA CITY, Fla. — Years before the advent of modern scuba gear in the 1940s, bridge builders and underwater construction workers labored in large, watertight, high-pressure chambers known as “caissons” -- dive bells that enabled the creation of iconic American structures such as the Brooklyn Bridge.

But, some of those workers returned to the surface feeling sick, achy, in shock or worse

Today, along with his team at the Navy Experimental Diving Unit, Naval Support Activity here, Navy Lt. (Dr.) Jonathan Casey Brown, a physician and dive medical officer, helps to ensure that understanding, treatment and research of caisson’s disease – now known as decompression sickness – keeps military divers safe and mission-ready.

History of ‘the Bends’

Around the turn of the 20th century, Brown said, underwater workers presented symptoms ranging from joint pain, skin rashes and neurological disorders such as numbness, tingling or weakness to the point of coma or death. These maladies, he said, mirrored those that military explosive ordnance disposal and special operations swimmers might face in missions involving extreme depth, coldness or currents.

“Although no one knew at the time what caused these afflictions, as research developed from caisson disease to ‘the bends’ to decompression sickness, doctors have developed a better understanding of how that occurs,” he said. “Mainly, it’s a load of nitrogen in the body as you’re increasing pressure of the environment -- and when you decompress, that nitrogen causes symptoms.”

Think of it as shaking a can of soda, with increased pressure causing bubbles and gas that will dissipate –but the ‘”fizz” occurs when that pressure is prematurely released. When bubbles gather around joints, the effect can be so painful that people commonly bend in agony, hence the name.

Navy divers inspect gear inside the ocean simulation facility that mimics pressurized ocean conditions at the Navy Experimental Diving Unit, Naval Support Activity Panama City Division, Panama City Beach, Florida. (DoD photo by EJ Hersom)

Bends, Body

The longer and deeper a dive, the more critical methodical decompression becomes, Brown said. As human tissues absorb more nitrogen, gas will present little or no problem to a diver remaining at pressure. But a sudden decrease in pressure forces the nitrogen from the tissues and into the blood stream.

“There’s a controlled decompression back to the surface at an extremely low rate of ascent, and that allows a greatly reduced risk for sickness,” Brown explained. “We deliver 100-percent oxygen to the diver in certain periods, and if it’s done in a timely fashion, the person has a good outcome.”

Since the NEDU’s specialized team of dive medical officers, research psychologists and physiologists can conduct manned biomedical research, development, testing and evaluation using rigorous scientific discipline, the unit is able to simulate extreme and diverse missions in an ocean simulation facility while keeping their test subjects safe and comfortable.

“We allow for proper clothing, warmth, food, water, toilet, showers … so that way people are taken care of while they’re decompressing,” Brown said.

Brown said one method NEDU uses to prevent decompression sickness is the Navy Dive Manual, which features tables indicating the decompression periods necessary to keep illness from occurring. For example, if a diver’s mission takes him or her 60 feet under water, the maximum decompression time is going to be 60 minutes.

“In the 1920s, developing decompression tables was much less standardized than today, so we’re still working on analyzing decompression schedules in the dive manual and improving them in a standardized, scientific venue,” Brown added.

Safety is Paramount

Although NEDU works closely with an institutional review board that oversees all human subject research to improve dive tables and lower the risk of diving-related injuries, what happens when limits must be deliberately pushed?

Brown said most NEDU human subjects are Navy divers and other military members. They are recruited openly, without coercion, and on an individual basis with informed consent of associated risk, he added. Brown also assured that the test subject information NEDU gains from the research remains confidential and is “de-identified,” which he said is one of the paradigms of the institutional review board when it assesses test protocols.

Despite an overall solid safety record, Brown acknowledged that NEDU research can bring adverse outcomes or injuries to their human subjects.

“While sometimes that may be the outcome we look for, we have a highly skilled, large medical team that’s here to support any medical emergencies that occur,” he explained. “In order to prevent as much injury as possible, our researchers, engineers and people tasked to do the test protocols here … are all part of a team that evaluates and looks to expose any kind of undue risk to our human subjects.”

DoD’s Unique Asset

Still, through their chains of command, research subjects enthusiastically volunteer, Brown noted, explaining NEDU involvement differs greatly from a typical Navy diver’s experience.

“There’s less work in maintenance on ships or salvaging, and there’s more work on experimental research,” Brown said. “The benefit for the nation, for the world, is important for these guys as well as for the command and for the Navy.”

The Navy divers are specifically trained to run the test facilities unique to the Navy and the Defense Department, and they undergo intensive training to understand and capably service the systems.

NEDU, Brown said, is an important asset to advise on proper equipment and newer, advanced technologies divers can use to better operate and perform their missions and duties. “Ultimately, NEDU is about protecting the warfighters and supporting their missions in all communities around the world,” he said.

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