U-M physicist receives grant to tackle the bends
ANN ARBOR—When divers stay at depth too long, or ascend too quickly from depths of more than 33 feet, they can experience “the bends,” or decompression sickness.
Decompression sickness happens because when a person is diving, they breathe air at a higher pressure. Nitrogen gas is dissolved in blood and other tissues such as the spinal cord, and when divers ascend, this gas precipitates back out of these tissues and collects in bubbles. Previously, researchers believed that this sickness was caused because the nitrogen gas bubbles ballooned as they collected, compressing spinal cord tissue.
Jens-Christian Meiners, a professor of physics and biophysics at the University of Michigan, observed recently that the bubbles may not just compress spinal tissue: they may tear it. He has received a $10,000 grant from Divers Alert Network, an organization devoted to scuba diving safety, to investigate this hypothesis further.
When nitrogen bubbles in the spinal cord, it can be serious. Divers can experience bladder dysfunction, sensory and motor issues, back pain and paresthesia—numbness or tingling of the skin. These effects can last a month or longer, even with treatment.
If this damage was caused by gas compressing the spinal cord, standard treatment of decompression sickness—hyperbaric oxygen therapy during which patients breathe oxygen in a pressurized room—should resolve the side effects. Instead, hyperbaric oxygen is only partially effective, with a quarter of patients having symptoms a month or longer after the accident, according to Meiners.
The grant continues a summer project Meiners led with undergraduate students in 2018 and continued through the academic year. That project made a model system that mimics spinal cord fluid using gels injected with gas bubbles. The students compressed and decompressed the gels to study how gas bubbles behaved inside them.
“The first thing we noticed when we looked at these gels is that the bubbles were not forming like a balloon, like you would expect in an elastic medium,” Meiners said. “Instead, they were actually peeling and fracturing the gels.”
Meiner suspects that when a nucleated gas bubble—or a bubble that grows by accreting other bubbles—grows during and after ascent, it tears the surrounding tissue. As the bubble continues to grow, the fracture spreads and further damages the nerve tissue.
In the current project, Meiners and his students will examine spinal cord tissue from cows. Placing the tissue in a pressure cell, they will compress the sample until it is under about six times as much air pressure as you experience at sea level, or ATA, and leave it pressurized for 48 hours. Then, they will subject it to a cycle of decompression and compression. Using a high-resolution magnetic resonance imaging machine, or MRI, they will observe how these gas bubbles form—and create damage—in the spinal cord.
“We think this may have implications for traumatic spinal cord injuries in general,” Meiners said. “The thought is that the high pressure oxygen could help in regenerating tissue. Our hypothesis is maybe there’s more to it: putting damaged tissue under pressure may be similar to compressing a wound and stitching it back together.”
Their work may present a new paradigm for how compression sickness generates. Their findings may also lead to better approaches for treatment.
Meiners and his team also received support from Mcubed, a U-M initiative that provides seed money for research projects to faculty-led teams. Expertise in MRI imaging is provided by Joan Greve, an assistant professor in the U-M Department of Biomedical Engineering, and Osama Kashlan, an assistant professor in the Department of Neurosurgery, provides the clinical background for the work.