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CNS Considerations in Scuba Diving

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How Your Diving Fitness Can Be Affected By Your Central Nervous System Health

By Dr. Hugh Greer, DAN Southwest Regional Coordinator

Attention Deficit Disorder (ADD)

This brain disorder, usually recognized early in life, is manifested by an inability to concentrate or sustain attention. It may or may not be accompanied by physical hyperactivity. ADD is a significant (but over-diagnosed) cause of learning disability. The problem usually improves with age.

Fitness & Diving: At its worst, ADD can be so pronounced as to prevent a prospective student from learning the simple skills necessary for safety. This could present a significant hazard in many areas, including both driving and scuba diving. ADD is usually not that intense, however. Fitness to dive can best be assessed by looking at social, school, athletic and job performance. Note that because some ADD patients take medications, they should consider the potential impact of medications while diving.

Medication Used in Treatment: No testing has ever been done to determine interactions between high partial pressures of nitrogen and the medications used to treat attention deficit disorder. Two drugs currently in use are Ritalin(r) (methphenidate) and Dexedrine(r) (dextroamphetamine). Both are heavy-duty stimulants that leave most adults "wired." However, they often have a calming and somewhat paradoxical effect on children with attention deficient disorder. This desirable effect is less apparent as children grow older.

Post Brain Tumor Surgery

The type of brain tumor is one that is surgically treated or removed. This covers a lot of ground. Some brain tumors are benign - once it's removed, the person is cured of that particular tumor. Some brain tumors are cancerous and may return. Removal of either type of tumor - benign or cancerous - sometimes results in substantial loss of neurologic function; at other times there is no loss of function at all.

Fitness & Diving: This depends on all the factors above, and others, too. Individuals should be counseled that if cerebral DCI or AGE occurs, they may be at risk for significant residual symptoms due to pre-existing CNS problems. Another item to consider: Brain tumors may cause seizures, a definite contraindication for diving. Consider:

  1. The extent of the physical handicap;

  2. The presence of seizures or the need for anticonvulsant medication;

  3. Surgery by itself does not constitute a diving hazard: when you dive, there is no pressure shift inside the head. The outside / inside pressure is the same, so no shift in structure occurs, and diving will have no effect on remaining tumor cells.

  4. Surgery done through the nose (as in the removal of a diseased pituitary gland) may be a special case because of increased risk of barotrauma to the sinuses or nasal passages, which may have been traumatized during the procedure.

  5. A defect in the skull itself may require special protection from physical trauma: piercing the skin over the defect while underwater poses a greater infection hazard than when at the surface.

Medication Used in Treatment: Some cancer treatment medications may affect the patient's lungs. A return to diving may necessitate a pulmonary evaluation.

Cerebral Vascular Accident

Stroke, or loss of blood supply to the brain, causes damage to part of the brain, or bleeding from a blood vessel in the brain, which results in similar injury. Strokes come in all sizes and shapes, and the resulting disability depends on size and location of the event.

Fitness & Diving:

  1. Most strokes occur in older people. The stroke itself identifies the person as one who has advanced arterial disease, thus a higher expectation of further stroke or heart attack.

  2. The extent of disability caused by the stroke (e.g., paralysis, vision loss) may determine fitness to dive.

  3. Vigorous exercise, lifting heavy weights and using the Valsalva method for ear-clearing when diving all increase arterial pressure in the head and may increase the likelihood of a recurrent hemorrhage.

  4. While diving in itself entails exposure to elevated partial pressures and elevated hydrostatic pressure, it does not cause stroke.

  5. There is certainly increased risk in diving for someone who has experienced a stroke. Exceptional circumstances may exist, such as cerebral hemorrhage in a young person in whom the faulty artery has been repaired with little persisting damage. This type of recovery may permit a return to diving, with small risk. Each instance, however, requires a case-by-case decision, made with the advice of the treating physician, family and diving partners. Consulting a neurologist familiar with diving medicine is also advisable.

  6. There is a similar concern for significant residual symptoms, as with post brain tumor surgery.

Cerebral Palsy

This describes brain injury, present at birth and which is manifested by some degree of weakness. This includes a wide variety of clinical illnesses, ranging from "walks abnormally" to very severe and disabling handicaps. Some cases present accompanying seizures, learning disability and speech defect.

Fitness & Diving: Diving fitness depends entirely on the extent of disability in the individual case. Candidates with mild problems may qualify; candidates with more severe disabilities may qualify through one of the scuba programs for disabled people. The absence of seizures and the ability to master the water skills are particularly important. For participation in scuba, case-by-case selection is needed.


This disorder of brain function causes episodic alterations of consciousness, called epileptic seizures. Abnormal electrical discharges in the brain cause these episodes; they may occur without warning, and they may vary in character from a brief loss of attention to violent, prolonged convulsion. People may outgrow the condition; it is often, but not always, controlled by medication.

Fitness & Diving: Loss of consciousness or loss of awareness while underwater carries a high risk of drowning or embolism from an uncontrolled ascent. An analysis of motor vehicle operators with epilepsy has shown that a seizure occurring behind the wheel will result in an accident in nearly every instance, but no evidence exists that diving with compressed air scuba to the accepted 130 fsw limit increases the risk of epileptic seizures. One is no more likely to seize while diving than while driving: the risk is the same. There is no useful data to determine the potential for injury in divers with epilepsy.

Current doctrine among diving medicine physicians advises that individuals with epilepsy not dive. Those with childhood epilepsy, who have outgrown the condition and have been off medication for five years, still face a slightly increased risk of a seizure. To make an informed decision about diving, these individuals should discuss this with their personal physicians, families and diving companions.

Medication Used in Treatment: Anti-seizure medication acts directly on the brain and may interact with high partial pressures of nitrogen. This may produce unexpected side effects. (See nervous system medical effects.)

History of Seizures Without a Clear Diagnosis of Epilepsy

This is a cloudy question since many variables can cause transient alteration of consciousness. These alterations of consciousness include fainting, a reduction of blood pressure, which is very common in young people, an alteration in heart rhythm that is more common in older people, effects of medication and psychological events, such as hallucinations.

Fitness & Diving: As with epilepsy, any loss of consciousness underwater is likely to have a bad outcome. When diving using nitrox or mixed gas as a breathing gas, increased partial pressures of oxygen can increase the likelihood of seizures. Increased carbon dioxide may also increase seizure risk.

The best advice is to get a precise diagnosis of the cause of altered states of consciousness: effective treatment is often available. You cannot make a reasonable fitness-to-dive decision till this is sorted out. It may take some time and a visit to a neurologist or other specialists. Ask your doctor first.

General Concerns About Taking Medication While Scuba Diving

Many of the conditions discussed are treated with medication. These include anticonvulsants to prevent seizures, antidepressants and sedatives to alter behavior, pain medication and a host of others. In addition to the intended effect, many drugs have undesirable side effects, which vary from person to person and are not entirely predictable. The list of side effects, while far from complete, includes these most common states: drowsiness, dry mouth, blurred vision and slowness to urinate.

Additionally, these medications have not been tested in divers while diving or in a controlled hyperbaric environment: this type of assessment of risk for the diver cannot be performed. There may be an interaction between the medication and high partial pressures of nitrogen, producing an unexpected side effect such as anxiety or panic.

Fitness & Diving:

  1. Alertness is important; medications while diving can affect a diver's alertness;

  2. Increased pN2 (partial pressures of nitrogen) causes narcosis and can be expected to increase the drowsiness side effect of many drugs such as antihistamines and medications for motion sickness.

What to do:

  1. Read the package insert of the drug you are taking;

  2. Ask your doctor;

  3. Pay attention. The medication may affect you in an unexpected way. Ask again;

  4. If you start a new medication, or change medications, don't dive until you have had a couple of days to feel it out. If your medication makes you drowsy on the surface, expect it may have greater effect at 75 fsw. In this case, you should either not dive, or discontinue using the medication. Always check with your physician before stopping a prescription medication.

Head Trauma

"Head trauma" refers to a head injury sufficient to cause prolonged unconsciousness or persisting brain dysfunction. Mild head injury without unconsciousness rarely has lasting effects.

Fitness & Diving: Two principal concerns exist:

  1. Post-traumatic epilepsy - This risk is directly related to the severity of the injury and the time elapsed between the injury and your plans to dive. Penetrating head wounds with brain disruption have a high risk of post-traumatic seizure; head injuries resulting in brief unconsciousness do not. With mild head injuries, risk falls sharply with time; with penetrating head wounds, long-term risk is less predictable.

  2. Cognitive loss. Defects in memory, understanding and concentration are obvious risks in diving. This is best evaluated by social, school and job performances. If these skills are intact, there is probably no reason to restrict diving. Diving in itself does not worsen the effects of head injury.

Migraine Headache

A migraine headache is a periodic, usually one-sided, throbbing ache, sometimes preceded by warning signs and symptoms and of variable severity.

Migraine, though dreaded, is common. More than half the people in the world will have some experience with migraine during their lives, and about 5 percent will see doctors. A few of these will suffer significant disruption of their activities.

Fitness & Diving: Migraine poses little danger to divers. Even those with frequent migraine do not usually experience an increased incidence while diving. An elevated level of carbon dioxide in the blood, which occurs with decreased ventilation and breath-holding / hypoventilation, can theoretically precipitate a migraine headache because carbon dioxide (CO2) causes vasodilation in the brain. Increased levels of oxygen in the blood (which occurs in diving as well as in hyperbaric chambers) has been used with variable success to treat severe migraine, because it is a powerful brain vasoconstrictor.

Very complex migraine, with visual loss or paralysis, might lead to confusion in diagnosing a diving accident. However, little data exists to suggest that migraine poses a significant hazard to divers. Severe and incapacitating migraine headaches while in the water would create a hazard for the individual. People with severe and incapacitating migraine should probably not dive.

Multiple Sclerosis (MS)

This immunologic disease occurring in young and middle-aged people is characterized by episodes of neurologic dysfunction, often separated by remission. The extent of disability is quite variable. Treatment has improved in recent years.

Fitness & Diving:

  1. There is no evidence that diving in itself has an effect on the disease. About 20 years ago an unsuccessful effort was made to treat MS with hyperbaric oxygen. Patients neither suffered nor benefited from this treatment series.

  2. Persons with MS are advised not to exercise to the point of exhaustion and to avoid becoming chilled or overheated. Diving candidates with MS should respect that advice.

  3. In each individual case, consider whether the candidate can handle the physical load and master the water skills. Diving candidates should talk to their neurologist about diving.


Paralysis (paraplegia) or weakness (paraparesis) of both legs may result from spinal cord injury such as accidental fracture, decompression sickness, muscle disease such as poliomyelitis or a brain injury such as cerebral palsy or stroke.

Fitness & Diving: Diving fitness depends on the cause and the extent of disability in each individual case. Considerations include:

  1. The extent of physical disability that may determine whether the candidate can perform the required water skills. High spinal cord injury (closer to the head) may compromise breathing. How? Respiratory signals come from the spinal cord at the c4-5 level, so a fracture at or above that level will likely paralyze the diaphragm. A fracture at the mid-thoracic (chest) level will paralyze the legs, while a fracture at c5-6 will cause severe paralysis of the arms as well.

  2. Diving in itself does not cause further injury unless the diver gets decompression sickness involving the spinal cord. In that case, because the spinal cord is already damaged, there may be an increased risk of residual disability, even after prompt treatment.

  3. There are reliable programs (e.g., associations of disabled divers) designed to accommodate diving candidates with such problems. These programs emphasize the importance of avoiding DCS by careful diving practices.

  4. As with multiple sclerosis and other CNS considerations, deciding on whether to dive with paraplegia requires a case-by-case decision. Decide after consultation with your physician.

DAN Southwest Regional Coordinator Dr. Hugh Greer is a practicing diving medicine neurologist and former Underwater Demolitions Team (UDT) officer.

From the May/June 1999 issue of Alert Diver