Dr Peter Wilmshurst has been a qualified doctor for over 25 years. He has served on the BSAC Medical Committee since 1977 and also advises the HSE on diving.
I recently had major surgery on my intestine and need to know whether there is a safe period for which I should wait before returning to diving, whether I should restrict myself to shallow dives, what ill-effects I might suffer as a result of the surgery when diving and what symptoms to watch out for.

After major surgery of any type, there are general recommendations about returning to diving. Do not do so if the wound has not entirely healed or before the surgeon has given the all-clear to dive. Generally, I advise people to lay off for at least six weeks after that. However, there will be specific recommendations depending on the surgery.
I dont know its precise nature, but whenever there is intestinal surgery the concern is that gas trapping could occur and cause barotrauma to the gut. Symptoms of this might be abdominal pain; bloating; breathlessness as movement of the diaphragm is restricted; or vomiting. It is difficult to be more precise without further information.

Could diving help treat MS
My wife has dived in the past, but was recently diagnosed as suffering from multiple sclerosis. She is left with residual numbness and poor movement in one hand, which might improve with time. Should she continue to dive We have read about the so-called benefits of hyperbaric oxygen in multiple sclerosis, but what would the effect of a raised partial pressure of nitrogen be

There are a number of issues here. First, anyone diving with any sort of pre-existing neurological disease could be at risk because of reduced power, sensory input or co-ordination. However, they can dive under a scheme for diving with disability.
Adjustments to training and diving procedures will need to be made and the individual might need to dive only with an experienced companion.
Second, if a neurological bend is suffered, those providing treatment wont know which finding is the result of the bend and which the pre-existing disease. Treatment will usually be more difficult and recovery less likely, because of the reduced reserve capacity.
Finally, we do receive enquiries from people with multiple sclerosis because of the suggestion by some doctors that some of its effects might be improved by hyperbaric oxygen therapy.
I think the evidence for this is poor, and that if there is a benefit, it is very mild. The effect of diving could not be expected to have any benefit on the disease process in multiple sclerosis, though a psychological benefit in some people (by increasing confidence) cannot be excluded.
Testing for a hole in the heart
I have recently suffered from what appears to be an unaccountable bend. After long recompression treatment I am now waiting to have tests for a PFO before being given the all-clear to dive again. What do these tests involve

Decompression illness (the bends) can be caused by failure to follow a safe dive profile, either because of missed decompression stops, a rapid ascent or both.
When bends occur after a theoretically safe dive profile, the diver usually has a physical cause for the condition, and this could be lung disease causing barotrauma.
More frequently it is the presence of a PFO (patent foramen ovale), a hole in the heart which is necessary for life in the uterus, but which normally closes after birth. In about a quarter of the population it does not close, though in most cases the residual hole is very small. In fewer than one person in 20 it is large enough to be a diving problem.
After many dives, bubbles form in the veins. These are filtered out by the lungs but a large PFO will permit significant numbers of them to pass across from one side of the heart to the other, bypassing the lungs.
If sufficient bubbles get across to the left side of the heart after a dive, they can damage the brain or spinal cord to cause a neurological bend. They can also cause skin bends.
Before return to diving after the bends, you should be tested to make sure you dont have a large PFO.
There are a number of methods but I would recommend contrast echocardiography.
This involves an ultrasound examination of the heart, essentially similar to the type of ultrasound scan that pregnant woman have of the uterus but with the transducer placed on the chest rather than the abdomen.
The ultrasound is painless. The only slight discomfort is the need to inject some contrast into a vein in the arm to outline the PFO, but this requires only a very small needle and is no worse than giving a blood sample.
Other tests for detecting a PFO are not any better, in my opinion, and are more uncomfortable.

Quick consultations
I have been prescribed omeprazole (tradename: Losec) for reflux oesophagitis and am concerned that diving might increase the side-effects of the drug. Should I be diving while taking it

I dont think omeprazole is likely to cause problems when diving, though reflux oesophagitis can do so occasionally.
This condition causes acid to pass up out of the stomach into the gullet, and can be associated with a hiatus hernia. It can cause vomiting, which would clearly be a problem if it occurred under water. However, usually there will be no problem from either the disease or this treatment.

I have suffered from a defective hip joint for a number of years and am getting near to the stage when I should have the joint replaced. Is it possible to dive with an artificial hip joint

There are lots of divers with artificial joints. Provided things have healed up well after surgery, you should be able to dive.

In July I had an accident in which I suffered a compression fracture to my spine. I crushed one of my vertebrae, reducing it by 50 per cent. Will this mean longer decompression, or will my depth be restricted when diving I have been told that my back will take the weight.

I dont think there is proof that injury to the bones of the spine affects risk of decompression illness.
As you point out, the main concern is whether your back will stand up to carrying cylinders around.

I am thinking about starting scuba diving as a hobby but two years ago I had an epileptic fit for which I am now on medication (phenytoin capsules). Am I allowed to dive when I am on the pills

Diving is not permitted for individuals who have had a recent fit, in case they have another convulsion under water and drown.
Diving is not allowed for anyone who takes anti-convulsants (drugs to stop fits) because this type of drug is thought to increase the risk of nitrogen narcosis.

I have been put on Dothiepin for depression. Is it compatible with diving I have been off it for five nights but there is no way that I would dive the way I feel now.

Do not dive. Dothiepin and depression are both reasons to avoid diving. The condition and its treatment are each likely to impair judgment when diving.