During her decades-long career as a commercial diver, Sherri Ferguson has gone beneath the surface of the sea more times than she can remember. What stand out clearly for the local researcher, though, are the several instances when she experienced a state of mental impairment called nitrogen narcosis.
When breathed under pressure, nitrogen, which makes up 78 percent of our atmosphere, has an intoxicating effect akin to that of alcohol. Also known as the “rapture of the deep”, nitrogen narcosis sets in, generally, when divers go to depths of 30 metres or more.
“It kind of comes on suddenly, just like after you’ve had a couple of drinks,” Ferguson tells the Georgia Straight by phone. “In hindsight, you’re clearly impaired.”
Ferguson, the director of the Environmental Medicine and Physiology Unit at SFU—which researches human performance in extreme environments—is studying nitrogen narcosis and other health effects of deep-sea diving, including sudden cardiac events. With funding from the U.S. navy, she hopes to improve safety among occupational and recreational divers alike. (A 2003 survey estimated that about 25,000 recreational divers used B.C. dive-charter services that year, and that approximately 10,000 people enrolled in basic and advanced diving courses.)
She recalls a local dive about five years ago where she was doing routine underwater work but with great difficulty. “I can remember tying a knot, but I did it the wrong way and was trying to undo it so I could do it properly, and I was just fumbling around with this rope,” she says. “If I would have been thinking clearer, I would have just cut it, but I just kept trying to undo it, and any other solution wasn’t coming to my mind.
“You only have so much time,” she adds. “When you’re impaired, you’re not as aware of time. It seems to go faster or slower; your perception is off. For recreational scuba divers who don’t have as much experience, if you’re not monitoring your air supply you could run out.”
Higher brain functions such as reasoning, memory, concentration, and attention can all be affected by nitrogen narcosis, and the consequences can be disastrous. According to the book Diving Medicine for Scuba Divers, divers in this altered mental state could fail to follow instructions or the dive plan or be inattentive to buddy signals. “Emergency signals will go unheeded, emergency air supplies will not be offered, weight belts will not be released, rescue attempts will be crude and amateurish,” the authors write. “Survival instincts and responses may be dampened. The safety of both the diver and his buddy are compromised.”
Between 30 metres and 50 metres, divers may feel overconfident. At 50 metres, anxiety and sedation can set in. Go deeper and confusion and terror can strike. So can hallucinations and loss of consciousness.
“It intensifies with depth and can result in poor judgment and decision-making,” Ferguson says.
“Any diver that’s working below 100 feet is working impaired, and that can lead to mistakes and can be life-threatening. Could you imagine carpenters or welders or people in any other profession having to go to work with four beers in them? Routinely, divers have to do that, only it’s not beer but impairment that’s similar to drinking.”
Factors that are known to exacerbate the effects of nitrogen narcosis include fatigue, anxiety, inexperience, hypothermia, and recent consumption of alcohol or use of sedative drugs, including seasickness medications and marijuana.
Meanwhile, divers are also at risk of cardiac events brought on by the effects of decreasing pressures at the end of a dive. In B.C., anywhere from 20 to 28 percent of diving fatalities are a result of heart attack, Ferguson says, either during ascent or upon reaching the surface. She’s personally known people who have died this way.
“These were very experienced divers,” she says. “It was so sad.”
The actual figures could be much higher; oftentimes the cause of death is noted as “drowning”, but it’s possible a cardiac event occurred first.
What perplexed Ferguson was that these individuals were not exerting the same kind of physical effort involved in more strenuous physical activities like hockey. Many had no history of cardiovascular disease. Some were under age 30.
“What I thought was, ‘Something is going on,’ ” she says. “There’s something triggering these heart attacks. It happens in older divers, men reaching 50 or 60, but in young, healthy adults as well. We want to see if diving itself has an effect on the heart that’s causing some kind of arrhythmia.”
Ferguson’s research into nitrogen narcosis and cardiac events involves two approaches: using a hyperbaric (pressure) chamber to investigate the cognitive effects of various concentrations of oxygen used by divers; and recording and analyzing divers’ heart rate, blood pressure, core body temperature, biomarkers in the blood, and blood-oxygen saturation during simulated hyperbaric dives. She is also recording cellular electrical activity using an electrocardiogram, providing insight into subjects’ physiological responses at the cellular level.
“We need to understand what diving’s doing to the heart,” she says. “It places much higher stress on the heart than we figured. If we can get that information out to physicians and individuals, we can help avoid those cardiac events.
“We should be educating people who are at increased risk of heart attack as well,” she adds. “We need good education programs telling people that if they have problems breathing underwater or their chest feels tight or they’re having trouble catching their breath, even if they’re experienced divers, they could be experiencing something bigger.”