What are the physiological effects on the brain during scuba diving?

Physiological Effects on the Brain During Scuba Diving

Scuba diving exposes the brain to multiple significant physiological changes that can lead to serious neurological complications including arterial gas embolism, decompression illness, and oxygen toxicity, all of which can cause permanent brain damage or death if not properly managed. 1, 2

Pressure-Related Effects

Increased Partial Pressure of Gases

• Nitrogen narcosis: At depths beyond 30 meters, increased partial pressure of nitrogen affects neurotransmission, causing impaired cognitive function and judgment, similar to alcohol intoxication 1
• Oxygen toxicity: At depths of 60-70 meters, high partial pressure of oxygen can cause:
  • Seizures
  • Central nervous system dysfunction
  • Impaired respiration 3

Blood Redistribution Effects

• Immersion causes blood shift to the thoracic cavity (approximately 700 ml)
• This results in:
  • Increased intracranial blood volume
  • Altered cerebral perfusion
  • Potential changes in ventilation-perfusion matching 1

Barotrauma and Gas Embolism

Arterial Gas Embolism (AGE)

• Occurs when expanding gas ruptures lung tissue during ascent
• Gas bubbles enter pulmonary circulation and travel to the brain
• Clinical manifestations include:
  • Sudden loss of consciousness
  • Seizures
  • Focal neurological deficits
  • Potential death 1, 4

Decompression Illness

• Neurological decompression events comprise 80% of major decompression problems 3
• Brain effects include:
  • Multiple cerebral infarcts
  • Confusion and altered mental status
  • Sensory disturbances
  • Visual disturbances including double vision 4, 5

Patent Foramen Ovale (PFO) Risk

• Present in approximately 25% of the population
• Creates right-to-left cardiac shunt allowing venous bubbles to bypass lungs
• Significantly increases risk of:
  • Cerebral arterial gas embolism
  • Neurological decompression illness 3
• Divers with history of severe decompression illness should be evaluated for PFO 3

Long-Term Neurological Effects

• Neuroimaging studies show increased frequency of ischemic brain lesions in experienced divers 3
• Commercial deep divers report:
  • Concentration difficulties
  • Paresthesia in extremities
  • Abnormal EEG findings
  • Symptoms correlating with diving depth and history of decompression sickness 6

Breath-Hold Diving Risks

• Repetitive breath-hold diving with short surface intervals can cause:
  • Multiple cerebral infarcts
  • Brainstem lesions
  • Sensory numbness
  • Visual disturbances 5

Epilepsy and Seizure Risk

• Scuba diving is contraindicated for people with epilepsy due to:
  • Immediate drowning risk if seizure occurs underwater
  • Increased risk of decompression illness
  • Potential complications from nitrogen narcosis 2
• The British Thoracic Society and American Heart Association recommend against diving for individuals with seizure disorders 2

Prevention of Neurological Complications

• Proper ascent and descent techniques to prevent barotrauma
• Adherence to decompression schedules
• Avoiding diving with conditions that increase risk (epilepsy, PFO)
• Limiting depth and duration to minimize nitrogen loading
• Proper training and equipment maintenance 4

Common Pitfalls and Caveats

• Neurological symptoms may be subtle or delayed after diving
• Symptoms resembling "fatigue" or "mild headache" may actually represent serious decompression illness
• Any neurological symptoms after diving should prompt immediate medical evaluation and consideration of hyperbaric oxygen therapy
• Divers often underreport symptoms, leading to delayed treatment and worse outcomes 1, 4

Remember that any neurological symptoms following diving should be treated as a medical emergency, as early recognition and treatment with hyperbaric oxygen therapy significantly improves outcomes for decompression illness and arterial gas embolism.