Some of the same gases in the air we breathe to stay alive can become harmful, even deadly, at increased atmospheric pressure.
“Oxygen becomes toxic and nitrogen starts to act like a narcotic that will anesthetize you in some of these high pressure, or hyperbaric, environments encountered by the military in deep-sea diving or submarine operations,” said Jay Dean, PhD, professor of molecular pharmacology and physiology at the USF Health Morsani College of Medicine.
USF Health’s Jay Dean, PhD, is one of the world’s leading experts in hyperbaric neurophysiology.
Listen to Dr. Dean talk about the hyperbaric lab.
Dr. Dean, one of the world’s leading experts in hyperbaric neurophysiology, has attracted more than $4 million in external funding from the Office of Naval Research (ONR) Undersea Medicine Program, since joining USF in 2006.
The USF Hyperbaric Biomedical Research Laboratory he established and directs houses various styles of pressure chambers, which mimic the environmental conditions challenging divers who breathe pure oxygen as they swim deeper and longer. The largest, at 3.2 tons, is specially designed for use with an atomic force microscope and patch clamping apparatus to help researchers determine how gases with different solubility affect brain cell function.
To date, Dr. Dean and his USF colleague, Dominic D’Agostino, PhD, have adapted electrophysiology, radiotelemetry and various types of microscopy techniques for use under hyperbaric pressures, including fluorescence, confocal and atomic force microscopy.
“Atomic force microscopes are common, but not atomic force microscopes placed under hyperbaric pressure,” Dr. Dean said. “In our lab, we’ve been able to apply very powerful research tools to unique conditions.”
Dr. Dean’s lab will soon send its second graduate student to work as a physiologist at the Navy’s medical research center. “At USF, we are helping train the next generation of undersea medicine experts in the novel techniques needed to study human performance under extreme conditions.”
The USF Hyperbaric Biomedical Research Laboratory houses various pressure chambers, including a 3.2-ton one specially designed for use with an atomic force microscope, which mimic the extreme environmental conditions challenging deep-sea divers.
Shedding light on role of oxygen toxicity in seizures
Dr. Dean started his career studying the effects of carbon dioxide on the neural control of breathing and cardiovascular function. His collaborations with the Department of Defense and Undersea Medicine program shifted his primary focus to the role of oxygen toxicity in seizures as well as the toxic effects of carbon dioxide retention.
Recently, Dr. Dean’s team expanded the scope of their hyperbaric neurosciences research by probing the cellular mechanisms of nitrogen narcosis, a major factor limiting divers’ safety and performance. This new research direction was supported by a transfer of $700,000 of equipment to USF from the Navy’s Experimental Diving Unit in Panama City, FL. In addition, Dr. D’Agostino’s team, housed with Dr. Dean in the Hyperbaric Biomedical Research Lab, has broadened the work on hyperoxia to include studies that may lead to non-toxic cancer therapies combining dietary supplements and hyperbaric oxygen.
Over the last decade Dr. Dean’s research has helped shed light on the role of hyperbaric oxygen toxicity in triggering seizures. The condition can be a life-threatening by-product of breathing too much oxygen at high ambient pressures that impacts deep-sea divers as they swim deeper and longer.
Deep-sea divers can be at risk for oxygen toxicity seizures, a life-threatening condition caused by breathing too much oxygen at high ambient pressures. – U.S. Dept. of Defense photo
Navy SEALs are especially at risk because they wear a closed circuit rebreather, to mitigate the narcotic and other debilitating effects of nitrogen and carbon dioxide breathed under increasing ocean pressure. The special device filters out these gases in such a way that bubbles do not appear on the water’s surface – useful in helping avoid enemy detection. However, the additional stealth comes at a cost. The ratio of oxygen the divers breathe greatly increases the deeper they plunge (essentially becoming pure oxygen) and, when combined with physical exertion and mission stress, can lead to nausea, dizziness, seizures, and even coma or death – all symptoms of oxygen toxicity.
A possible countermeasure, anti-seizure sedatives, requires high doses that could impair warfighters’ mental and physical performance.
Without a reliable way to treat oxygen toxicity or predict which divers are more prone to seizures than others, the Navy takes rigorous precautions to restrict all divers to no more than 10 minutes in 50 feet of seawater.
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Applications extend beyond undersea medicine
“This risk of central nervous system oxygen toxicity limits oxygen’s use — not only in diving operations, but also its clinical applications in hyperbaric oxygen therapy,” Dr. Dean said.
Hyperbaric oxygen therapy, which increases blood oxygen to temporarily restore blood gases and tissue function, can help treat unhealed wounds, burns, crushing injuries, decompression sickness, carbon monoxide poisoning, and other medical conditions. The therapeutic benefit might be maximized if the doses of hyperbaric oxygen administered could be boosted without the risk of CNS oxygen toxicity.
In their search to find solutions, Dr. Dean and colleagues analyze the response of individual brain cells to the powerful effects of oxygen and other gases under altered pressure. In the laboratory’s hyperbaric chambers, they measure changes in brain cell membranes and electrical activity, and the damage of oxygen-induced free radicals.
The researchers also monitor physiological changes in the breathing and heart rate of normal rats moving about in a chamber mimicking the environment of an increasingly deep dive. An electroencephalogram (EEG) shows electrical signals in the brain in real time, indicating the hyperexcitability that precedes and peaks with oxygen toxicity seizures.
An intracellular recording of the electrical signaling by a brain cell (middle trace) in a rodent brain slice that is stimulated by hyperbaric oxygen (top trace).
Promising discoveries to predict, delay seizures
The USF group made what could be a key discovery – the breathing rate of the rats exposed to pure oxygen increases several minutes before a seizure starts. “This may be a biomarker – an early physiological signal that predicts the impending seizure,” said Dr. Dean, who was principal investigator for the study published in the Journal of Applied Physiology.
If this early-predictor hypothesis bears out in larger animal models, he said, the next step would be to work with the Navy to devise and test a mask-fitted with a device designed to monitor divers’ breathing underwater. The ultimate aim: preventing oxygen-induced seizures to safely allow Navy SEALs to dive deeper and longer.
Another of the laboratory’s major findings evolved from an idea by Dr. D’Agostino, Dr. Dean’s former postdoctoral fellow who is now an associate professor, to harness the power of ketones, natural compounds produced by the body when it burns fat during periods of fasting or calorie restriction.
They’ve focused on better understanding how the ketogenic diet — a special low-carbohydrate, high-fat diet that elevates blood ketones and alters brain metabolism — produces anticonvulsive and neuroprotective effects. The diet has been successfully used to treat drug-resistant epilepsy or other seizure disorders.
Dr. Dean with laboratory colleagues Angela Poff, PhD, research associate, and Dominic D’Agostino, PhD, associate professor, all members of the Department of Molecular Pharmacology and Physiology.
Dr. Dean comments on the team’s two approaches to studying oxygen toxicity seizures.
Working with collaborators in academia and industry, USF continues to develop and test naturally derived and synthetic supplements that will more rapidly mimic the therapeutic effects of ketosis without the problems associated with adhering to the ketogenic diet.
In a first of its kind study, Dr. D’Agostino and Dr. Dean tested whether feeding laboratory rats a ketone ester and placing them in the hyperbaric chamber simulating underwater conditions could delay oxygen toxicity seizures. It worked. Their study was published in the American Journal of Physiology: Regulatory, Integrative and Comparative Physiology. They also hold a patent on the use of the USF-developed ketone ester, a highly efficient fuel for the brain, to prevent CNS oxygen toxicity.
More research is needed, but the experiments pave the way for a ketone supplement that would allow Navy SEALs to dive longer while protecting them against seizures, Dr. Dean said. “If what we’ve observed in rat model experiments holds true in humans, the Navy diver should be able to increase the amount of time spent at a depth of 50 feet of seawater (10 minutes) by 600 percent… which means that the divers could get more work done with fewer dives.”
The USF Hyperbaric Laboratory will be included in an upcoming independent documentary on nitrogen narcosis, which features Sherri Ferguson, a colleague of Dr. Dean’s from Simon Fraser University in British Columbia, who studies the health effects of narcosis in deep-sea divers.
Unmatched expertise in hyperbaric cellular electrophysiology
Earlier this year, Sherri Ferguson, director of the Environmental Medicine and Physiology Unit at Simon Fraser University in British Columbia, visited Dr. Dean’s lab to observe and collaborate on some experiments investigating brain cell response to nitrogen under pressure. Ferguson, helping to make a documentary on nitrogen narcosis and its health effects in deep-sea divers, brought along the independent filmmaker who included an interview with Dr. Dean in the piece.
When breathed beneath the ocean’s depths, nitrogen can create state of mental impairment similar to the intoxicating effect of alcohol.
Ferguson recently visited Dr. Dean’s lab to collaborate on some experiments investigating brain cell response to nitrogen under pressure. “Dr. Dean has the only cellular hyperbaric electrophysiology lab of its kind in North America,” she said.
Ferguson says she was attracted to the USF Hyperbaric Biomedical Research Laboratory by Dr. Dean’s development of continuous intracellular recordings measuring how mammalian neurons behave under varying gas and pressure conditions.
“Dr. Dean has the only cellular hyperbaric electrophysiology lab of its kind in North America. His expertise in this field is unmatched, so I was excited to learn from him,” she said. “To leave him out of a documentary on cellular mechanisms of narcosis would not accurately reflect where the research is today and where it is going in the future.”
A microscopic image of neurons hyper-excited by exposure to pure oxygen under high pressure in the hyperbaric chamber.
Something you might not know about Dr. Dean:
He has spent 33 years researching the physiological problems of flight encountered by World War II pilots and their crews, who flew at high altitudes in unpressurized aircraft and suffered hypoxia from lack of oxygen and decompression sickness from low pressure.
Dr. Dean is writing a book on advances by the Allies in aviation physiology research during the war and has presented on this topic across the United States. His impressive collection of historical documents, manuscripts, films and other artifacts from Wright Field Aeromedical Laboratory (Dayton, Ohio) and several universities and medical centers documents the pioneering work on oxygen equipment, G-suits, high-altitude parachute escape, explosive decompression and development of the first pressurized airplanes.
This photo from the Mayo Historical Unit Archives shows the team of researchers from the Wright Field Aero Med Lab and Mayo Aero Med Unit before the aircraft Nemisis, a B-17E testing platform used during World War II, takes off for a study of the opening shock of a parachute at high altitude. Physiologists trained a 145-pound St. Bernard dog, Major, (lower right) to parachute — simulating the jump of a man. Major wore protective clothing and an oxygen mask during his descent.
Photos by Katy Hennig, USF Health Communications
