Archive of Spotlight Feature Articles

Submerging the body and the brain: Sea Grant scientists probe the physiology and psychology of scuba diving

by John Karl

"It’s extremely important that divers have sufficient information to make informed choices about what they’re doing. It’s all a matter of determining acceptable risk."

-- Charles Lehner

Three decades ago, the popular Undersea World of Jacques Cousteau television show made scuba diving seem as natural as a walk in the park. Yet today, as millions of people dive for recreational, commercial, and military purposes, scientists still have much to learn about the complex ways the human body and brain respond to the underwater environment.

With support from NOAA Sea Grant, the University of Wisconsin (UW) has been advancing diving physiology knowledge for a quarter century. In the early 1980s, Wisconsin Sea Grant researchers helped design some of the first dive computers, now widely used by divers to monitor how long they can safely remain at depth.

Even as far back as the 1970s, Wisconsin Sea Grant was supporting the work of prominent diving physician Dr. Edward Lanphier, who conducted some of the first controlled experimental assessments of the causes and effects of the bends and other forms of decompression sickness or illness. This line of inquiry continues today.

The “bends,” also called “limb bends,” refers to discomfort or pain in joints or bones that divers may feel if they dive too deep, stay down too long and surface too quickly. The sensations are mostly caused by bubbles of nitrogen forming in bone or other tissues. Other forms of decompression illness (not considered limb bends) involve bubbles in the lungs, brain and spinal cord.

Divers sometimes dive deeper, stay down longer, or surface faster than conventional guidelines recommend. However, the risks of doing so have been poorly understood.

Today, Dr. Charles Lehner and his colleagues are changing that. Lehner, a physiologist at the University of Wisconsin-Madison, has succeeded Lanphier in leading Wisconsin Sea Grant’s diving physiology research.

Lehner and his colleagues have established several cornerstones of modern diving physiology. One is that diving profiles influence which body tissues are most likely to be damaged from nitrogen bubbles. For example, Lehner showed that multiple short dives of 50 feet or more tend to produce injuries to the spinal cord and central nervous system, causing temporary paralysis, severe disablement or even death. Longer, shallower dives, however, are more likely to injure the long bones of the arms and legs or to induce “the chokes,” a condition in which a diver has difficulty breathing because of bubbles in the lungs.

Lehner’s team also showed that persistent limb bends, lasting roughly a half day or more, can lead to the death of bone tissue, called dysbaric osteonecrosis or DON. This was the first demonstration of the link between the bends and DON in a controlled setting, and it has important implications for diving medicine. DON often leads to arthritis in bone joints, or osteoarthritis. In severe cases, osteoarthritis weakens the ends of the long bones in the arms and legs and can result in joint collapse and debilitation.

Lehner and his colleagues are corroborating these laboratory findings with real-world observations of seafood divers in Puerto Rico and Maine. Many of these divers practice the short and deep “bounce” diving that places them at high risk for DON.

With support from the U.S. Navy, Lehner and his colleagues are also evaluating the risks associated with long stays at elevated pressure in submarines and underwater research habitats such as NOAA’s Aquarius facility—and they are developing procedures to minimize the dangers of quick escapes from these high-pressure environments.

Wisconsin Sea Grant has also supported extensive research into human psychological responses to the underwater environment, particularly panic responses. UW-Madison exercise psychologist William Morgan spearheaded this work.

Morgan surveyed more than 500 experienced recreational scuba divers and found that more than half reported panic behavior at least once while diving. One strategy for preventing panic might involve identifying people at high risk for panic episodes before they take up scuba diving. Morgan and his colleagues found that a standardized pencil-and-paper measure of trait anxiety can predict panic behavior with 88 percent accuracy.

“If a test like this were used to identify beginning divers at high risk for panic, those people might be dissuaded from pursuing diving, or they could be specially trained to cope with diving-induced stresses,” Morgan said.

Morgan has discovered panic responses may be related not only to physical exertion, but also to perception of physical exertion. Using hypnosis to alter people’s perceptions of effort while exercising, Morgan found their heart rate, blood pressure and regional brain blood flow depended as much on their perceptions of exercise intensity as on the actual intensity. According to Morgan, this suggests that accurately perceiving one’s exertion while diving, which is typically low, could reduce divers’ risk of panic responses. He emphasizes, however, that these studies were land-based, and it is not yet known how these findings might be adapted to diving training programs.

As more people discover and explore the underwater world, Wisconsin Sea Grant looks forward to advancing our knowledge of how the brain and body respond to this challenging but fascinating environment.

For more information see:
NOAA’s Aquarius site: http://www.uncw.edu/aquarius/
Wisconsin Sea Grant site: http://www.seagrant.wisc.edu/

[6/30/03]

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