MEDICAL FAQs

QUESTION

ANSWER

I agree, this is odd, to get what seems an obvious case of DCS after relatively simple shallow diving.

But before you embark on investigations for a PFO, ask yourself this.

Did you do anything to make the dives more DCS prone, ie increase on-gassing or decrease off-gassing. Dehydration, diarrohea, increased exercise before and after diving, a sawtooth profile, or any rapid ascents. All these can affect your ability to get rid of the nitrogen in your body.

If the answer to the above is no, then you ought to get a PFO check. This is a specialist cardiac investigation and needs GP or diving doc referral.
If one is found, and remember that up to 30% of us have one, then you need to weigh up the need to have it closed against your desire to dive again.

Some doctors say if it is small and you don't want to undergo operative closure, then diving on Nitrox using air tables will increase your safety margin.

QUESTION

ANSWER

Knowing what an obsessive lot us divers are, I would never label being out of the water for 10 months as trivial! This is a bit of a complicated tale though. It will help to do some explaining, and I apologise in advance as this will be a little technical... let’s start with the blood’s journey through a normal heart. When the heart beats, the left side contracts and squeezes blood through the body’s arteries. The blood then returns to the right side of the heart through veins. When the right side contracts, it pumps the blood to the lungs, where it picks up lots of oxygen so it’s ready for its next journey through the arteries. This cycle is repeated about 100,000 times every day, meaning that the human heart beats around 35 million times in a year, and an incredible 2.5 billion times in an average lifetime. Not bad for an organ the size of two clenched fists.

When dealing with PFO’s and the like, the concept you need to understand is right to left shunting, where some of the blood bypasses the lungs and goes straight from the right side of the heart to the left. This means that those pesky nitrogen microbubbles, rather than being filtered out by the lungs, go straight past and enter the normal circulation, potentially leading to decompression illness. A PFO is the most common form of right to left shunt seen in divers, but there are others, including ASD (atrial septal defect) and pulmonary (lung) arteriovenous malformations (AVM). The latter is what your doctor is suggesting, as it is most likely in the absence of an obvious PFO on echo – this is often the case when the bubbles show up after more than 5 cardiac cycles. A pulmonary AVM is basically an abnormal communication between the pulmonary artery and pulmonary vein, which again allows blood (and bubbles) to bypass the lungs. They can be diagnosed by CT scan or pulmonary angiography. Most are congenital (ie present since birth). They can be treated, either surgically or with embolisation, but this depends very much on the exact type and individual circumstances of each case. Whether diving is possible afterwards again is difficult to say - the cardiologist would have to be sure that there is no residual right to left shunting. So there’s no definite answer here until you’ve been fully investigated I’m afraid. Fingers crossed.

QUESTION

ANSWER

Hmm, tricky one here. Is a diet that tends you towards ketosis likely to bring on DCS, despite the increased amounts of fluids taken at the same time? I can see it causing cramps, see your body finding it harder to find energy to dive and all that, and see odd osmotic issues causing increased cell fluid retention and so less ability to off-gas but it may well be a red herring. With a second mystery hit, and with skin DCS to boot, I think you need to look up the PFO route for the reason.

If this is confirmed, then closing the hole would allow you to return to diving. So some good news as I think the other doc is being over cautious with a total ban at this stage. If you turn out to be PFO negative, lets have a rethink.

A point to note here, I think its best not to go onto fad diets if you are diving a lot. Eat less, move more. An easy mantra.

QUESTION

ANSWER

Yes you do need a PFO check, and definitely before you do another dive. The easiest way of doing this is for me to refer you to a cardiologist with experience in these tests. I can do it remotely, if you join e-med, and you can get to London as we have a good man here to do it. But this would be a private referral and it costs about 180 quid for the scan. Or you could ask your NHS GP, and join the queue behind all the "more needy" cases.

QUESTION

ANSWER

Not many people realise that we are all born with a hole in the heart. It lies between the top 2 chambers of the heart, called the atria. When we’re curled up in the womb it’s the presence of this hole that allows oxygenated blood to pass from the placenta through the foetal heart and round the body, bypassing the lungs (which are full of amniotic fluid and therefore not much use). At birth, what’s supposed to happen is that the hole closes; the blood then gets directed around the lungs to pick up its oxygen, before being pumped around the body. This hole is called the foramen ovale (because it’s oval-shaped), and sometimes it doesn’t fully seal over, resulting in a “patent” or permanently open hole – the PFO, of which you may have heard. So a PFO is one type of atrial septal defect (ASD); there are others, of all sorts of shapes and sizes, and I suspect yours must have been rather large if it needed to be operated on at 2 years of age.

To understand why ASD is a problem, a little explaining is required. The right and left sides of the heart are normally separate. The left side of the heart pumps blood around the entire body, and so the pressure is much higher than on the right, which just pumps blood to the lungs. If you have a hole between the two sides, then the right side of the heart becomes exposed to the higher pressure of the left, which in time will overload it. This is called a “left to right shunt”. Fluid will then accumulate in the lungs causing breathlessness, and ultimately the heart will fail. If the ASD is small, this process may take many years, but a large hole can cause heart failure in childhood.

These days the hole is easily closed with an umbrella-like device which is threaded through a groin vein into the heart, and deployed on either side of the ASD (or PFO for that matter). After a few months enough scar tissue has formed to occlude the defect completely, and separate the two sides of the heart again. So at the ripe old age of 32, if you are able to exercise without any symptoms, the heart should be normal, to all intents and purposes. An echo test to put some numbers on the heart function would be useful, but I anticipate it will show a heart that’s perfectly capable of diving.

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ANSWER

Quite a bizarre set of symptoms there, but I’ll throw in my two pennies/cents. I’m presuming from your question that these episodes didn’t cause any problems in other organ systems, ie. they purely involved your vision. In which case, despite the apparent response to surface oxygen, we can put DCS and/or arterial gas embolism lower down on the list, as they tend to present with other manifestations too. We should consider simple things such as contact lens problems, medication side effects or local infections as well, as they can cause all sorts of visual disturbances. Typically though, they will be irritating or painful and involve watering or other surface reactions; not the impression I get from your description. My feeling is that these are probably migraine-like phenomena, which have been reported in the literature after exposure to pressure. These can be triggered by diving, or just happen as a coincidence, but are sometimes very difficult to distinguish from DCS. There is a well-publicised link between visual auras and patent foramen ovale (PFO, the “hole in the heart” that can predispose to DCS), which confuses the picture even further. As this is recurrent and you’re intending to dive for a long period in a remote location, my advice would be to get this fully checked out by a cardiologist with diving medicine experience before your trip.

QUESTION

ANSWER

We’re impaled on the particularly spiky horns of a classic diving doc’s dilemma here: migraine or bend? Difficult to distinguish the two, as both can result in similar visual tomfoolery. The commonest eye-related DCS symptoms include blurring, tunnel vision and loss of parts of the visual field. These can also occur as part of the aura of a migraine, and as we know, headaches can be a presenting symptom of DCS. A tangled web indeed. Your unprovocative dive circumstances don’t ring DCS alarm bells, but we all know that a normal profile doesn’t exclude a bend. Other features unconnected with vision and headache (eg. joint pain) might lead one to suspect DCS, but you don’t mention any other symptoms. So my advice would be to see a neurologist about this before diving again. There are other conditions to consider, eg. TIA (Transient Ischaemic Attack, otherwise known as a “mini-stroke”), and as the symptoms have recurred and are worsening, you really need a full work-up to be sure what the cause is. An echocardiogram looking for PFO should be part of this.

QUESTION

ANSWER

Your query is a good one and this issue is the subject of much debate in the diving medicine fraternity. The main problems causing the controversy are poor standardisation of the diagnosis of DCS, and of PFO. Without applying the same criteria to all data, it’s difficult to interpret. Furthermore, measuring the diameter of a PFO is one thing, but grading of the resultant shunt is a tricky task; quantifying its size by counting the number of bubbles crossing is difficult and very operator dependent. This is the reason that studies looking at the relationship between DCS and PFO vary so much in their conclusions, quoting an increased DCS risk with a PFO of anywhere between 2.5 to 4.5. Importantly though, the overall risk for DCS in recreational divers remains very low, something of the order of 0.005% to 0.08%, or 1 in 3500 dives. So even in the worst case scenario, multiplying this by 4.5 still equates to a very small number. What it boils down to is how much risk you are willing to accept. Ultimately what you have to remember is that it is not a PFO that causes a bend, it is nitrogen bubbles. So I humbly suggest your objective should be to minimise your bubble load at all times, using the simple measures I’ve outlined in this article.

QUESTION

ANSWER

PFO is such a common condition, and the actual number of bends so low, that screening everyone would be unethical – although the test is very safe, there are risks attached, and a large number of divers would end up requiring closure procedures unnecessarily. However, certain groups are thought to be more prone to PFO. Those who suffer migraines with aura are one. Aura is the term given to a neurological disturbance that precedes or accompanies your typical migraine headache. The commonest symptoms are visual disturbances (eg. zigzag lines, blurred or tunnel vision) but pins and needles, tingling, weakness, speech problems and even strange tastes or smells are possible. There is some evidence linking this type of migraine with the presence of PFO, and if you are keen on a career in commercial diving then one could make a case for screening to pre-empt a later episode of avoidable DCS. However, it has to be remembered that not all bends are due to PFO, so fixing the hole doesn’t make one “immune” to future bends. But once repaired, you’re carrying the same risk as a diver without a PFO, so you shouldn’t be discriminated against.