1 December 1999
Are scuba divers mad, or only those with heart conditions?
by Kate Melville
While numerically speaking not a huge proportion of the population scuba dive those who do should take note of the following. Up to 25% of people are affected by a common heart condition that when combined with scuba diving this can have direct links to things like skin rashes, brain lesions and serious neurological problems.
According to Dr. Michael Knauth, a neuroradiologist at the University of Heidelberg Medical School, Germany, "We feel testing for this heart condition with a special ultrasound examination should be included in the fitness-to-dive exam that people take before being certified to scuba dive. That way, divers will know if they have the condition and can take precautions to reduce their risk."
The researchers used magnetic resonance imaging, to look at scuba divers with might have patent foramen ovale (PFO), a common and usually harmless condition afflicting about 25% of the population. They found that divers have more PFO and are more likely to have brain small lesions, scars, or areas of dead tissue. To make matters worse they are also at a higher risk of suffering from decompression sickness (the bends) as well as serious neurological problems such as vertigo and transient or even permanent paralysis!
"It is unclear whether the brain lesions can cause long-term problems, but common sense would tell you if you have enough of them and they're in the right places, they could cause problems, such as memory disturbances or difficulty concentrating," said Dr. Knauth.
PFO exists in all humans when we are born and it is basically just a usually harmless opening in the connection between the right and left sides of the heart. For 75% of us it naturally closes after birth. When people scuba dive, inert gas bubbles form in venous blood and normally they are pumped by the heart to the lung, however in people suffering from PFOs these gases may travel throughout the body and into the brain where they can cause small lesions. It is these small lesions that Dr. Knauth believes may cause small infarctions that lead then to dead tissue and or scarring in the brain. The bubbles traveling through the body also might cause blockages in small arteries, leading to decompression sickness.
Before they are certified to dive people should be taught the rules that apply to decompression (descending and ascending at a specific rate) and then in theory they should and follow these guidelines regarding the depth of the dive to avoid getting the bends. Unfortunately even when divers follow these rules rigorously they can still have problems with PFO's. This means that divers in this risk group need to take further precautions.
During the study a cranial MRI was performed on 88 divers with brain lesions being detected in 12 divers. Only one lesion each was found in 7 divers who did not have a PFO, but 37 lesions were found in the 5 divers with PFO (of those 4 divers had up to 16 lesions )! "Divers with PFOs should reduce the depth they are descending to, not stay deep too long, ascend slowly, increase the time they spend above water between dives and avoid several descents during one dive," said Dr. Knauth.
The second part of the research program compared 24 divers who had an unexplained diving incident where they had correctly followed the rules of decompression. These were compared with 14 divers who accompanied them and did not suffer have any symptoms of decompression sickness. Of this group 19 of the 24 divers (almost 80 percent) who had had an unexplained diving incident had a large PFO, detected by echo-contrast transcranial Doppler ultrasound. By way of contrast none of the divers without a large PFO had brain lesions.
This work indicates that divers and their medical needs require some important reviews but as Dr. Lnauth noted, "These recommendations are not fool-proof, but they should lower the risk (of diving)."