An increasing number of patients with controlled diabetes, asthma and other diseases are getting the green light for an activity that was once off limits: scuba diving.
There is little evidence to suggest that having asthma or diabetes should preclude a patient from venturing underwater, according to researchers at the Dive Medicine Symposium at Rutgers University.
"There's not a lot of strong data to suggest that diabetics are at increased risk" of potentially serious adverse events, said Dr. Michael Madsen, a fellow in undersea and hyperbaric medicine at the University of Pennsylvania. Likewise for other depth-related illnesses such as arterial-gas embolism in the lungs or decompression sickness, also known as "the bends," he said.
The same thinking applies to most asthmatics, said Dr. David S. Lambert, who specializes in hyperbaric therapy at the Hospital of the University of Pennsylvania.
However, those with severe disease are often disqualified from diving after failing a required pulmonary test.
Earlier concerns about diving with diabetes led to bans in the United States, United Kingdom, and parts of Europe. The bans stayed in place until the mid-1990s -- and until 2004 for France.
Madsen said the major issue for diabetic divers is the potential for an underwater hypoglycemic episode that causes unconsciousness. These episodes are usually triggered by increased metabolic demands, since patients are "using more energy than usual when they're diving," he said.
They're particularly problematic for insulin-dependent diabetics, because their regular does of the hormone may be too high for someone undergoing increased activity.
There are also concerns about myocardial infarction (a heart attack) among diabetic divers from unrecognized vascular disease, Madsen said, although these threats are more frequently detected today and divers know about such risk in advance.
Even so, few studies have found evidence of an increased risk of adverse events among diabetic divers.
Data from research in 2005 performed by the British Sub Aqua Club, the diving regulatory agency in England, found only one instance of hypoglycemia among 447 diabetic divers who completed 14,000 registered dives.
And 2004 data from the Diver Alert Network (DAN), the diving regulatory agency in the U.S., found no symptomatic hypoglycemia cases among 80 divers on over 6,000 dives, although it did record some "fairly large glucose drops."
On the basis of that data and other studies, the American Diabetes Association guidelines recommend that divers remain physically fit and get regular exercise outside of diving.
They must also have no significant systemic disease, as well as excellent control of their diabetes, and their physicians "should have the final say in determining fitness to dive."
DAN guidelines recommend an annual physical that includes screening for heart disease if the diver is over age 40.
The agency also recommends that diabetic patients take blood glucose readings an hour, 30 minutes, and immediately prior to "splashing," or starting their dive.
Madsen said that blood glucose should be kept "a bit above normal" at 150 mg/dL since the diver will be using more energy than normal.
"When diving, we like to keep diabetics a little bit sweet," he said, adding that the dive should be cancelled if blood glucose tops 300 mg/dL.
For asthmatics, the biggest concern is having an attack underwater. And some studies have shown an increased risk for arterial-gas embolism or decompression sickness, Lambert said.
For instance, one study reported by DAN found that 12 percent of arterial-gas embolism victims had a history of asthma, and another found that asthmatics have a four-fold increased risk of decompression sickness.
But Lambert said the data were based on surveys and case reports, detracting from their strength and power.
A large study at the University of Rhode Island found only one asthmatic patient among 2,131 diving death records that they assessed.
Guidelines from the American Thoracic Society say that patients with well-controlled, stable asthma who have normal spirometry and "understand the risks of scuba diving … seem to have only a slightly increased risk over the general population."
Patients considering diving "should have their asthma severity and control reviewed, undergo spirometry, and have an action plan in place with access to emergency rescue medications," according to the guidelines.
Ultimately, the decision about permitting the asthmatic patient to dive is in the physician's hands, Lambert said.
He said patients with cold-induced asthma are immediately prohibited from the sport because exposure to colder underwater temperatures could trigger an attack. Likewise, exercise-induced asthmatics are disqualified from diving.
But those with mild intermittent and mild persistent asthma are "probably OK to dive," Lambert said.
"It's the patients with moderate persistent and severe persistent asthma … that I'm going to be most concerned about," he said.
He said physicians should base their decisions about a patient's ability to dive on chest X-rays, pulmonary function tests, and a thorough patient history -- and make all decisions "on a case-by-case basis."
Most importantly, the physician must be sure the asthmatic patient understands what he or she is getting into.
"Diving with asthma is all about patient education and understanding the risks," Lambert said.
Dr. Matthew Partrick, who specializes in emergency and undersea and hyperbaric medicine at Southern Ocean County Hospital in Manahawkin, N.J., said patent foramen ovale (PFO), literally a "hole in the heart" between the atrial chambers, increases a diver's risk of decompression sickness.
Dr. Alfred Bove, of Temple University and president of the American College of Cardiology who is an expert in diving and the heart, said most patients with cardiovascular disease can participate in recreational scuba diving as they would any other sport.
Bove said deciding which patients with heart disease should or shouldn't dive is an "art," because there is little data on risk.
As with asthma and diabetes, he said, decisions are made on a case-by-case basis. But in general, he said patients are diving "with stents, pacemakers, mechanical heart valves, or while they're taking blood thinners."
"Many people who have heart problems, can dive safely," he said.