In 1662, a British clergyman and physician now known only as Henshaw created the first hyperbaric chamber for therapeutic purposes. While this chamber was merely a sealed room with a system of bellows and valves, Henshaw theorized that the pressure changes he could modulate in his “domicilium” were of a benefit to both acute and chronic illnesses. In the more than three centuries since, hyperbaric oxygen treatments have proven effective for myriad conditions including decompression sickness (the “bends”), carbon monoxide poisoning, burn,s and non-healing wounds. And new research out of Tel Aviv University suggests that hyperbaric oxygen might also promote neuroplasticity—and dramatic improvements in outcomes—after brain damage.
How it works
It is the increased overall pressure found in hyperbaric oxygen chambers that helps reduce the volume of inert gas bubbles to treat conditions like the bends. But another side effect of the pressure change is an increased level of oxygen—the pressure compresses the oxygen molecules, providing an environment that can deliver oxygen to the body at ten times the amount available in normal atmospheric conditions.
“I call it a supernatural treatment,” says George Mychaskiw, chair of the department of anesthesiology at Nemours Children’s Hospital in Florida and an expert in hyperbaric medicine. “Not that it’s magic. But we don’t normally live at two or three atmospheres of pressure. Except for a few bottom-dwelling organisms in the sea, the behavior of oxygen at these difference pressures is outside the normal realm of biology, certainly outside the normal realm of human biology.”
That “supernatural” oxygenation has been shown to help promote healing in different types of wounds. “The tissue around a chronic wound may be getting very little oxygen because there’s very little blood flow to the center of the wound,” says Col. Brian McCrary, an Air Force physician and expert in hyperbaric medicine. “So by increasing the oxygen to the tissues, you help drive healing. Hyperbaric treatment also helps stimulate new blood vessel growth, which drives new capillaries into an area to help get more blood and oxygen into the affected area. And it’s also been shown to reduce inflammation, too.”
The combination of these benefits has led many to hypothesize that hyperbaric oxygen could be a good treatment for brain damage. Mychaskiw has demonstrated exactly that in animal models, yet it has been more difficult to prove in human trials. But Shai Efrati, a neuroscientist at Tel Aviv University's Sackler Faculty of Medicine, recently tested hyperbaric oxygen treatments on seventy-four people who had had strokes and were no longer improving.
Healing after stroke
Efrati and his colleagues had half the study participants undergo hyperbaric oxygen treatment for two hours daily five times a week for a total of forty sessions. The second control group received no treatment for two months, followed by two months of hyperbaric treatments. The researchers found that the patients who received hyperbaric treatment in the first two months showed remarkable clinical improvements including increased sensation, language skills, and movement ability—even if it had been years since the initial damage. Neuroimaging analyses also showed significant increased neural activity in damaged brain areas. The results were published in PLoS ONE earlier this year.
“After a brain injury, you’ll see several types of brain damage. The most severe is necrosis. That tissue is dead and nothing can be done. But surrounding that necrotic tissue, you see areas that still have some metabolic function. Those areas can be improved,” says Efrati. He argues that those cells are compromised, with enough metabolic activity to stay alive but not enough to fire and promote action potentials. The extra oxygen delivered by hyperbaric treatment, over time, helps those cells heal and regain normal metabolic function and firing potential.
Efrati and his team are currently running two similar trials on people with traumatic brain injury and Alzheimer’s.
A question of control
While many agree that Efrati’s data are promising, a prior study run by the U.S. Air Force found no significant differences between hyperbaric oxygen treatment and a sham treatment on patients with mild traumatic brain injury (TBI). Both groups showed significant improvement over the course of the trial. Those results were published in the November 2012 issue of the Journal of Neurotrauma.
“The sham treatment was just air at a slightly increased pressure,” says McCrary. “There are several possible explanations for why there were equivalent improvements but the most likely scenario is a placebo effect or just the effects of the intensive treatment and attention that the patients received over the course of the six-week trial.” McCrary says that future trials should be able to rule out those scenarios.
Mychaskiw is not surprised by the contradictory results. He argues that it is very difficult to design a good study to test the efficacy of hyperbaric oxygen treatments. “Patients are very aware of their surroundings, so people in any control group have to believe they are receiving some kind of pressure. It’s hard to rule out placebo or just the effect of receiving a treatment, any treatment ,” he says. “But it’s also possible that it’s not the oxygen that has the effect. It’s possible that the pressure itself has a therapeutic effect. There are a lot of factors at play—and it’s a very complicated thing to study.”
The Air Force is completing the analysis on three more trials that will be published later this year, which McCrary hopes will finally provide more definitive answers. But despite the lack of clear-cut clinical results, hyperbaric oxygen is already being used to treat brain damage resulting from conditions ranging from TBI to dementia to autism at specialized clinics across the globe.
“At the end of the day, hyperbaric oxygen is a relatively benign therapy. It’s very hard to hurt someone with hyperbaric oxygen at the pressures that are used,” says Mychaskiw. “And those who are currently using it become very evangelistic about it because they see, at least in their minds, dramatic, clinical improvement. My hope is that future studies will give us a better understanding of how and where and why it works. But we haven’t gotten those answers yet.”