Dr Ian Sibley-Calder has been a GP since 1988, is a medical referee for the UK Sports Diving Committee and is involved with hyperbaric medicine and commercial diving activities. He is a BSAC Advanced Diver and Club Instructor.

I have severe back problems. Some discs are herniating and partial disc removal has left me with some numbness in one leg, caused by pressure on the sciatic nerve. It is unclear if sensation will return. Other than avoiding basic trauma from lifting scuba equipment and boat travel, what kind of extra risk am I running regarding decompression illness Would diving be better avoided until sensation returns to my leg

There are theoretical concerns regarding increased risk of decompression illness in someone who has had spinal surgery. Disturbance of the blood vessels around the site of the surgery could lead to poor gas exchange and increased bubble formation, which in turn could lead to a spinal bend.
There is also the potential confusion that could occur regarding the nerve damage that has already occurred, when trying to diagnose a DCI episode.
    Diving might be possible if the neurological signs are stable, so you should be assessed by a medical referee. I would advise that any problems be recorded in detail (with a copy to yourself) for future reference, and that your diving should be conservative. You should make every effort to minimise nitrogen loading.

Equalising in helmet
What are the differences between diving with scuba equipment and using a US Navy-style Mk V helmet. Do you have to equalise changing air pressure when descending using the helmet If so, how is it done The Valsalva technique using your hands would be impossible.

Most modern commercial helmets have a small nosepiece against which the nose can be pushed, thus sealing the nose and allowing a Valsalva.
    Many other techniques allow ear-clearing, including the Frenzel, Lowry or Toynbee. Most are a variation of trying to close the nose, thrusting forward the jaw and swallowing, thus allowing air into the middle part of the ear via the eustachian tube.
    Experienced divers often have very mobile tympanic membranes and can descend to great depths before equalisation needs to take place. They also have the ability to auto-inflate their ears using less pressure, often simply by swallowing.
Medication for depression
Since completing my Club Diver course I have suffered a mild breakdown. I am presently on Fluoxetine (Prozac 20mg). I dont want to risk putting a buddy or myself in danger due to the medication, so I am not diving, but can I dive safely on it

Without knowing more details I cant comment on your fitness to dive.
    As a rule we dont like diving on medication that can potentially affect a divers abilities under water. Many medications for depression and anxiety do affect the mind and there are grave concerns as to how they might affect divers under pressure.
    Alongside this is the reason the person went on the medication in the first place. Depression is often associated with inability to concentrate properly, make decisions clearly and rapidly and to have increased anxiety/panic attacks. These symptoms are not compatible with diving.
    I have known divers who have dived successfully while on 5HT anti-depressants such as Prozac. They are usually at the end of their illness and have been stable for months without any symptoms. After being assessed individually (sometimes discussing their condition with their GP and partner), they were allowed some limited diving.
    We have no hard data on the safety of these drugs under pressure.
    My advice is: get well, get off the medication, and then start diving.
After the heart attack
Last March I had a heart attack due to a blocked artery. It was treated with an angioplasty and stent insertion, and I was put on aspirin and simvastatin. I have been physically active, with no problems. Can I return to diving

Heart attacks can cause significant damage, and before diving it must be shown that your heart can withstand a significant exercise load without stress.
    Stents open up the blocked artery, and are very successful but unfortunately some seem to block up, and symptoms return. The medication that you are on is acceptable (as far as we know).
You need to contact a local medical referee to arrange an up-to-date exercise ECG test and check that your heart is up to diving. Sadly, a common cause of medical death in older divers relates to heart problems under water, so these need to be taken seriously.
    You will probably not be allowed to train, and will be recommended to dive only with experienced divers in case of problems.

Are contacts OK
I hope to begin my Open Water course soon, and need to know whether it will be safe to dive with contact lenses

Many divers use soft, gas-permeable contact lenses without problems while diving. Consider how you would manage if you lost a lens while diving, both from a safety and cost point of view. Daywear lenses help in this respect.
    In training you will be expected to take off your mask several times and look for it. Many instructors (rightly) do not allow students to shut their eyes.
    I would avoid hard lenses, as there is increased risk of barotrauma to the eye and they can be forced off the eye as bubbles come out of solution beneath them, and cannot disperse easily.
Other methods of correction include prescription masks and laser eye surgery. Radial keratectomy is best avoided as it is associated with spontaneous rupture of the cornea, but the newer techniques using the eximer laser seem to be quite safe with diving once the cornea has healed.

Tinnitus and beyond
I have had tinnitus in both ears for six months after failing to equalise on a 20m dive. I felt intense pain, rose by a metre or so and forcefully equalised. My hearing was unaffected, according to tests, but what are the chances of the tinnitus going

Your severe ear barotrauma was caused by failure to equalise the ears and a forceful Valsalva.
    The tinnitus (noise in the ears) probably represents inner-ear damage and could have resulted from a rupture of the round window or haemorrhage and/or trauma of the cochlea, the shell-like structure that picks up sound waves and transfers them into electrical energy for the brain to hear.
The tinnitus is likely to be permanent. You are lucky your hearing has not been affected, though get this rechecked, as it can present later.
    Future diving would be unwise, as you would be prone to possibly even more serious events. Consult an ENT surgeon expert in diving problems.
Necrosis risk
I was a US Navy salvage diver for 20 years and have avascular bone necrosis . I have had both hips and my right knee replaced. After another six years with the merchant marine I couldnt walk or pass the physical needed to sail. I have requested permanent disability from the veterans administration and wonder what your thoughts are

Your claim is best dealt with by local medical experts and, if necessary, lawyers. However, bone necrosis is a subject that might start to concern sport divers as they go deeper and for longer on mixed gas. It can occur months, years, even decades after hyperbaric exposure and results in areas of bone dying, often next to joints, which can be destroyed.
    Avascular bone necrosis was first found in caisson workers and then commercial divers. There are now reports of it occurring in sport divers. The exact cause is unknown, but there is a relationship to the depth and duration of hyperbaric exposure.