Generalization is always difficult when giving advice about a specific medical condition, such as Diabetes Mellitus, and its relation to diving. Each applicant requires individual assessment with regard to the disease, its severity and control, and how well the patient understands both the disease process and the diving environment.

The role of the physician for the recreational diver is that of advisor to the patient, his family and possibly his fellow divers, and to provide information on the risks that the pathological process may represent in the underwater environment. Should such applicants then choose to ignore the advice given, the advising physician should not be subsequently liable.

In commercial diving, fitness standards are largely "black and white". Regulations limit the options for a physician with respect to certifying an individual as fit to perform a specific task. In addition, many commercial diving companies have their own stringent fitness standards as a precondition to employment and in such circumstances there is no place for a diabetic in the commercial diving field.

Diabetes Mellitus is a common endocrine disease resulting from a deficiency of or insensitivity to insulin. The disease spectrum is wide and ranges from the young child dependent on frequent doses of exogenous insulin to the elderly patient whose blood glucose level can be controlled by diet alone. Between these extremes is large group of patients controlled by diet and oral hypoglycaemic agents but who may sometimes require insulin for glucose control when under severe stress.

It is often forgotten that many diving trips are preceeded by a passage in an open boat. The diabetic who takes his insulin prior to departure and then is either unable to eat or suffers from repeated vomiting as a result of sea sickness is especially prone to hypoglycaemia.The stress of a dive addes to this unstable state may well precipitate a hypoglycaemic crisis. In addition, the travel and diving schedule may interfere with the normal eating timetable so essential for the maintenance of stability in diabetics.

Every physician who has been present at an insulin induced hyopglycaemic reaction can attest to the rapidity at which symptoms appear and the speed with which judgement is impaired. Rapid loss of consciousness occurs in a significant number of hypoglycaemic diabetic patients. The normal symptoms of impending hypoglycaemia; agitation, sweating, circumoral paraesthesia, palpitations and confusion are all effectively masked by immersion and the normal anxiety of the novice diver. In the more experienced diver, the narcotic effects of nitrogen may well disguise these symptoms further.

During a dive, any loss of consciousness usually results in the regulator being dislodged from the mouth so that the victim either apsirates water or has larynegeal spasm and becomes apnoeic. Unless the buddy is immediately to hand, the victim will drown. Such a situation necessitates an emergency ascent with the attendent problems of gas expansion (according to Boyle's Law) resulting in barotrauma to the lungs. If there is a significant nitrogen load, the missed decompression schedule will put both victim and rescuer at risk of decompression illness.

Physicians who are sympathetic to their diabetic patient's attempts to gain recreational diving experience often quote examples of world class athletes who have diabetes. Such physicians either forget or are unaware that the diving environment is totally different from the athletic field or tennis court, in its density, the rate in which pressure changes occur, and the distance from skilled medical assistance. Although most diving is safe and quite leisurely, the need for unplanned, severe, sustained exercise is always present. On the athletic field, the blood glucose level can be easily maintained with drinks and nutritional supplements. The carriage and consumption of these items in the course of a dive is not as readily achieved.

A diabetic hypoglycaemic reaction is most likely to occur towards the end of a dive at which time it will be associated with hypothermia, high nitrogen load, dehydration and fatigue, all of which predispose to and may exacerbate the effects of decompression illness.

The end organ complications of diabetes predominantly affect the cardiovascular and neurological systems. There is a premature onset of generalised arterial disease in diabetic patients which has wide ranging effects on the myocardium, the kidney and the peripheral circulation. Myocardial infarction occurs earlier in diabetics and may be more severe as it is often associated with arrhythmias or cardiogenic shock. Such infarcts may be painless, especially when the victim is immersed as this eliminates the orthostatic hypotension associated with pump failure.

Peripheral vascular disease which interferes with the circulation tp the limbs is profoundly affected by the hypothermia of immersion. It may also affect the rate of gas exchange in the tissues making the diver more liable to decompression illness.

The neurological complications of diabetes which may affect candidates wishing to dive include polyneuropathy, amyotrophy and autonomic neuropathy. Such neuropathies result in muscle wasting, glove-like anaesthesia of the limbs and a loss of deep tendon reflexes. These may be a source of confusion to any physician if the patient subsequently presents for recompression therapy. Autonomic neuropathy may result in bladder dysfunction and urinary retention, disturbed temperature regulation, postural hypotension and cardiac arrhythmais in times of stress. Loss of afferent supply from the myocardium may be a reason why diabetic patients are subject to "silent" or painfree myocardiac infarcts.

In the vascular system, free gas not only obstructs smaller vessels and destroys endontelial surfactant resulting in loss of integrity of the intimal layer, but there is also a surface effect of the bubbles which causes denaturation of protein, increased platelet and white blood cell adhesiveness and stimulation of the clotting cascade. A study reported Halushka et. al. showed that, in diabetics, platelet agglutination occured more rapidly in response to ADP, adrenalin and collagen as a result of increased activity of the platelet prostaglandin synthetase system.

Fibrin and platelet deposition around a bubble stabilise a bubble so that it is more difficult to remove by recompression. A diver with a significant nitrogen load who performs a too-rapid ascent may suffer from bubbles of gas forming in the tissues and venous capillaries. This decompression illness is associated with intravascular changes in protein, platelets and extravasation of fluid into the extracellular space. It follows therefore that a diabetic diver is almost certainly more likely to suffer from decompression illness than a healthy diver in the same circumstances.

This liability to decompression illnes is compounded by the earlier onset of obliterative vascular disease in diabetic patients. These vascular changes are independent of the quality of control of the blood glucose level. The pathology affects all levels of the vascular tree and, potentially, interferes with the kinetics of gas exchange and slows the elimination of nitrogen from peripherial tissues.

In all classes of diabetic patient the end organ disease is often more severe than the symptoms suggest and is unrelated to the level of control of the diabetes. The non insulin dependent diabetic is typically obese, middle aged and unfit. The diving physician can usually eliminate such a candidate on the grounds of medical problems other than just diabetes.

Although most recreational diving is safe, uneventual and conducted at a leisurely pace there are occasions when it becomes exceedingly stressful and there is a need for unplanned, severe, sustained exercise. A diabetic whose blood sugar is controlled either with insulin or other oral agents would be incapable of maintaining such an exercise level and should be guided into less exacting pursuits.

The insulin dependent diabetic is prone to hypothermia, hypoglycaemia resulting in loss of consciousness and decompression illness and consequently should be advised against diving.

Diabetics controlled by oral hypoglycaemics are usually obsese, unfit and are unable to maintain an acceptable exercise level.

The diabetic controlled on diet alone may be permitted to dive if he demonstrates adequate cardiorespiratory fitness and all other criteria tested at the diving medical are found to be within normal limits.