Diving After a Stroke

By Dr. Sawatzky

What is a stroke? This turns out to be a very difficult question to answer and even in a medical dictionary, the word is poorly defined ('a sudden and severe attack'). In this discussion I will be talking about central nervous system dysfunction (acute brain damage) due to disease of blood vessels. This can occur either because the artery has been blocked (ischemic stroke) or because the artery has burst (ruptured aneurysm, haemorrhagic stroke). In Canada and the USA, 80% of all strokes are ischemic while only 20% are haemorrhagic.

Stroke is the third most common cause of death in both Canada and the USA (second most common in women and fourth most common in men). It is slightly more common in men than women (male/female ratio 1.3) but more women die from stroke than men. There are approximately 50,000 strokes per year in Canada and over 300,000 Canadians are alive who have had a stroke (500,000 and 2 million in the USA respectively). If you have had a stroke and survived, the risk of having another stroke in the next 5 years is 42% in men and 24% in women). The major risk factors for stroke are hypertension, smoking, and diabetes.

Newer oral contraceptives (estrogen <50 micrograms) and postmenopausal hormone replacement therapy are NOT associated with increased risk of stroke.

When the circulation to part of the brain is interrupted, the cells supplied by that artery stop working. Depending upon the function of those cells, almost any sign or symptom is possible but the most common symptoms are slurred speech (47%), hemiparesis (muscular weakness affecting one side of the body, 42%) and hemiplegia (paralysis of one side of the body, 34%).

There are many causes of stroke. Ischemic stroke is usually due to thrombosis, embolism or hypoxia. In thrombosis, an artery in the brain clots or a clot may form in the artery before it enters the brain and extend (grow) into the brain. In embolism, a clot forms outside the brain, breaks off and is carried into the brain. In both cases, the clot will completely block the artery and stop the circulation. If the clot breaks down quickly, it will be pushed through the artery and the circulation will be restored. In this situation, the person will experience a sudden neurological sign or symptom that lasts for less than one hour and then clears completely. This is called a "transient ischemic attack" (TIA) or "little stroke". Ideally, this results in no permanent damage to the brain. The concern in TIAs is that they tend to recur and often are warning signs that the person is going to have a full blown, serious stroke.

In hypoxic stroke, the person has low blood pressure for some reason (heart failure) and the areas of the brain with a poor blood supply do not receive enough oxygen and die (border zone infarcts). Haemorrhagic stroke is usually due to rupture of a dilated artery (aneurysm) or bleeding into the brain tissue because of hypertension. The most common causes of stroke however are thrombosis and embolism. When a person suffers a stroke, it is very important that they get to an emergency department as fast as possible. If it can be proven that the stroke is due to clot (CT scan and neurological consult), drugs can be given to break up the clot and reduce the
amount of brain damage.

The circulation of the brain is quite complex. The major supply of blood to the front and sides of the brain is by the left and right carotid arteries. These arteries branch off the aorta near the heart (technically, the right carotid artery branches off the innominate artery) and run up the front of the neck to enter the brain. The blood supply to the back of the brain is via the vertebral arteries. These arteries branch off the subclavian arteries in the shoulders, run up inside the vertebrae of the neck and join to form the basilar artery at the back of the brain. Inside the brain, branches off these three arteries join to form a circle, the circle of Willis. This is the most common way in which the brain receives its blood supply but variations are quite frequent. This variable and redundant blood supply makes it very difficult to predict what will happen when a particular artery is blocked.

In a typical stroke some brain cells die, but others receive enough circulation to stay alive, but not enough to function normally. Over time, additional circulation will sometimes develop and these cells will return to normal function. A person who has suffered a stroke can expect improvement for up to two years after the event.

Let's move on to a discussion of the fitness of a person to return to diving after a stroke. The first task is to determine why the person had the stroke. The second task is to determine if the person has any of the other medical problems that are usually associated with stroke. Do they have damage in the major arteries (arteriosclerosis) to the brain, in the heart, in the peripheral arteries, or in the kidneys? Do they have hyperten

sion, diabetes, or any other medical problems? Once these questions have been answered, the physician will be able to make an educated guess as to how likely it is that the person will have another stroke. For example, a young person with no other risk factors or medical problems may suffer a stroke when an aneurysm ruptures or starts to bleed. The aneurysm can often be clipped off surgically and angiography might show that they have no other aneurysms. The risk of this person having another stroke is very low. Conversely, a person might have had an embolic stroke and have extensive disease in their carotid arteries, coronary arteries and peripheral arteries. The risk of this person having another stroke is extremely high, even with optimal treatment.

This estimate of the risk that the person will have another stroke is very important in determining if they should return to diving. There are no specific rules for this but I like the two following guidelines. In aviation medicine, a pilot is considered fit to return to work when the risk of them having a sudden problem (stroke, heart attack, etc.) is less than 1% per year. In this case, the probability of having the problem while they are actually flying is extremely small. For divers who get paid to dive (commercial divers), this is a reasonable risk for the "company" to assume.

For technical divers I use the following guideline. I think it is reasonable to do the dive when the risk of the dive, including the risk of having a medical problem during the dive, is less than the risk of driving to the dive site (driving in Toronto and driving the logging roads on Vancouver Island is quite risky!). For recreational divers, the diver has to decide what risk is reasonable, remembering the risk to their dive partners if they have a problem during a dive.

The diver who has had a stoke must also consider several other factors. First, the signs and symptoms of the stroke must have completely cleared or be stable (up to two years). Any residual problems must not interfere with the ability of the person to dive. This assessment must be made by the diver and a very experienced diving instructor. Any residual signs or symptoms will make the diagnosis of DCS/AGE extremely difficult. Therefore, these individuals should be unfit all forms of commercial, technical and recreational diving where DCS is a concern. They must dive VERY conservatively so that the likelihood of DCS is extremely small.

Most individuals who have had a stroke will also have cardiac or arterial disease. They must be evaluated for fitness to dive for ALL of their medical problems, not just for the stroke. This also includes their level of physical fitness.

When you have an area of dead cells in the brain, there is a greatly increased risk of
having a seizure (epilepsy). Although the risk is always elevated, if the person has gone two years without a seizure, the risk of having a seizure becomes low enough that all states and provinces will allow that person to drive a car (some have shorter waiting periods). Therefore, two years seizure-free would seem to be a reasonable waiting period before returning to diving. The proviso in this situation is that the two year waiting period restarts every time the person changes the dose of their anti-epileptic medication, including stopping it. Therefore, a person who had been on a stable dose of a drug for two years might return to diving. If they decided to stop the medication three years later, they really should stop diving for two years as their risk of having a seizure is increased by stopping the drug.

Finally, individuals who have had a stroke are usually placed on several drugs to reduce the likelihood of them having another stroke, or seizure. Each of these drugs must be evaluated to determine if it is reasonable for the person to dive while taking that medication.

As can be seen from the preceding discussion, it is impossible to categorically say that someone who has had a stroke is fit or unfit for diving. Everyone must be individually evaluated, using the outline above. However, most stroke patients will have to wait at least two years after the stroke for their neurological signs and symptoms to stabilize, and to determine their risk of seizures. Most will be unfit for diving because of other associated medical problems. Some will be unfit for diving because of residual dysfunction and others because of the drugs they need to take.

As most patients will be unfit for diving after a stroke, it is imperative that divers do all they can to reduce their risk of having a stroke. Ensure blood pressure and cholesterol are under good control, maintain a healthy weight, lifestyle, regular aerobic exercise program, and most importantly, DO NOT SMOKE!