The Brain and Diving

[Plane Trouble]

Hello Dr. Deco,

Basically I was wondering if you would shed some light on the reports that diving results in damage to the central nervous system. The results of different published studies go either way. Same for the ocular damage associated with diving...

What are your thoughts as to whether or not diving results in brain and eye damage?

Thanks,
John

 

[idocsteve]

Eet duzz KNOT!

 

[Dr Deco]

Hello John:

There are reports of changes to the brain as detected by MRI. These lesions are also found in non-divers. There is a degree of correlation with DCS and/or length of diving, however, so people are suspicious.

It is difficult to say that this is CNS damage, since changes are seen in the brain and cord in the absence of signs and symptoms. The same is true for the eyes.

I would not believe that recreational divers need worry. There is not much concern in military or commercial divers, and they are under considerable decompression stress.


Dr Deco :doctor:

 

[Bubbletrubble]

Certainly decompression stress can cause damage to the central nervous system (CNS: brain + spinal cord).

Can diving over several years (in the absence of any overt clinical signs/symptoms of DCS) cause long-term cumulative destruction of the CNS? Yes, it's possible that subclinical DCS can eventually result in CNS dysfunction. In fact, here's a study that looked at CNS structures in amateur divers using MRI:

Citation: Reul et al. 1995. 345(8962):1403-1405
Title: Central nervous system lesions and cervical disc herniations in amateur divers

Abstract

Permanent neuropsychological changes such as memory disturbances and depression have been found in professional divers, even in those who have never had decompression sickness. The changes are probably the result of intravascular gas bubbles insufficient to cause acute symptoms. We examined amateur divers with long histories of self-contained underwater breathing apparatus diving by magnetic resonance imaging and compared them with normal controls. Hyperintense lesions of the subcortical cerebral white matter and degenerative changes of the cervical disks were significantly more common in the divers. 27 of 52 divers had a total of 86 focal hyperintensities versus 10 of 50 controls with 14 focal hyperintensities (p<0·01). 32 divers had at least one degenerated intravertebral disc versus 9 controls (p<0·0001). These results suggest that amateur divers are at risk of accumulating lesions in the central nervous system and in cartilage.

I'd have to do a literature search on DCS-mediated damage to the eye. According to the hypothesized mechanism of injury above (bubbling resulting in repeated focal ischemia), I don't think that the optic nerve would possess any inherent protection to such ischemic injury. Furthermore, since the visual cortex exists as part of the brain, I'd think that the entire visual system would be susceptible.

I don't want to frighten you, but there's still so much we don't know about the pathogenetic mechanisms at play in DCS.

In case you were wondering, all forms of ischemia are not "bad," per se. There is a phenomenon called "ischemic/hypoxic preconditioning" (think tiny, transient mini-strokes) that may help protect against catastrophic neuronal loss in the setting of a massive cerebrocortical stroke. The molecular mechanisms underlying this phenomenon are complicated, but it is thought that protective factors (cytokines) such as HIF1-alpha (a.k.a. Hypoxia Inducible Factor1-alpha) are involved. Interestingly, HIF1-alpha has been shown to be able to induce neurogenesis in vivo and in vitro.

Hope this makes some sense.

Is there any particular reason why you asked your question? I can imagine that people with extensive diving histories may become interested in this due to recent diagnosis of some kind of CNS condition. Unfortunately, it would be very, very difficult to causally link a degenerative CNS disorder to decompression stress.

 

[Plane Trouble]

Well... I don't dive a lot... Maybe 3 or 4 times a year maximum. But for my job, I am commercial pilot and flight instructor and I certainly don't want damage from my other hobby - diving - to cause me to lose my job etc...

As best I know, I don't have any neurological damage. I am a very conservative diver. I don't really want to stop diving but at the same time as the reports come out I get more and more concerned.

In addition to not wanting to lose my job, I also don't want cognitive problems or a "reduced intellectual capacity" as I derive much of pleasure in life from pondering the world.

 

[LeadTurn_SD]

Hi Bubbletrubble,

Thanks for posting the link.

The size of the test population in those studies seems pretty small to draw any solid conlusions, other than to say "Hmmmm, that's interesting, I wonder if there is a connection...." (all I did was look at the summaries and noted the relatively low numbers of subjects, I'm lazy ).

I'd worry about the memory disturbances related to diving, but..... wait, what was I worried about again???

Oh, it must not have been very important, time to go diving.

Best wishes.

 

[Bob DBF]

It's an interesting topic but the real danger is an auto accident on the way to the dive site.

I think old age and beer consuemption will take a larger toll on my memory than diving, so far I can remember my dives, more than can be said for my nights out on the town.

Bob

 

[Bubbletrubble]

The size of the test population in those studies seems pretty small to draw any solid conlusions, other than to say "Hmmmm, that's interesting, I wonder if there is a connection...." (all I did was look at the summaries and noted the relatively low numbers of subjects, I'm lazy ).

@LeadTurn SD: I could PM you a download link for the full-length PDF (if you're feeling less lazy). Just let me know. The paper is only 3 pages long.

The study was done by a very competent German group from Aachen. You voiced a concern regarding the "low" number of subjects. I'd like to point out that there was sufficient statistical power to show a difference between groups (see the p values). As with most human clinical studies, subject selection was done on a voluntary basis. Investigators solicited experienced, active divers from local dive clubs. They took the first 55 respondents who fit the study criteria. "Experienced" was defined as having conducted at least 40 dives per year for the last 4 years. Then, 55 age-matched, gender-matched controls were selected from sport clubs in the local area. In total, investigators did MRI scans on over 100 different people -- that's pretty good in my book. MRI scans were evaluated in a random fashion by two neuropathologists. It wasn't a truly blinded study, but AFAIK hyperintense loci on T2-weighted images are fairly easy to pick out. The choices that the authors made in experimental design seemed to make sense.

Interestingly, in the diver group, only one person reported having a history of DCS. In this case, there was one DCS incident which resulted in transient sensory deficits in the right arm. That same person had a focal lesion in the left hemisphere. The paper doesn't say whether the location of this lesion was in the sensory cortex.

BTW, the study doesn't prove anything really. It is merely suggestive that diving even without overt signs and symptoms of DCS may be linked to long-term pathological changes (focal lesions) in the CNS.

 

[Lopaka]

Is there a medical distinction between brain "lesions" as seen on a MRI, and areas of stroke?

The study linked would be more useful if the subjects had also been screened for PFO, as others are making progress in linking that to "undeserved" DCS.

 

[Bubbletrubble]

Is there a medical distinction between brain "lesions" as seen on a MRI, and areas of stroke?

@Lopaka: No. A stroke is nothing more than dead CNS tissue that occurs when the neurons are deprived of a blood supply. It produces a lesion, just as many other CNS insults might. A stroke diagnosis is generally made by combining the clinical picture (acute onset of focal sensory/motor/cognitive neurological deficits) with imaged lesions in the corresponding area of the brain. "Lesion" is a very general term. It refers to any focal area of abnormality. In this 1995 study, T2-weighted images were used to image brain pathology. There are other techniques involving various contrasts available to neuroradiologists nowadays. For a nice summary of the difference among T1-weighted images, T2-weighted spin-echo, and the FLAIR MRI techniques, check out this link.

The study linked would be more useful if the subjects had also been screened for PFO, as others are making progress in linking that to "undeserved" DCS.

The purpose of the study was not to look at PFOs, "undeserved"/unexpected cases of DCS or the specific cause of DCS, per se. The objective of the investigators was simply to correlate the existence of CNS lesions with an active dive history. Interestingly, with the exception of one case in the diver group, none of the divers reported ever experiencing a formal DCS incident.

Put simply, the mechanism by which the CNS lesions occurred is beyond the scope of this study.