Scuba diving is an activity that places the human body in an environment of dramatically shifting pressures. The fundamental principle governing the risks is Boyle’s Law, which states that the volume of a gas is inversely proportional to the surrounding pressure. As a diver descends, increasing ambient pressure compresses air spaces; conversely, ascending causes trapped air to expand. This expansion is the primary mechanism by which pre-existing medical conditions become dangerous, potentially leading to barotrauma, or pressure-related injury. Because the underwater environment is unforgiving, any condition that impairs consciousness, compromises gas exchange, or prevents pressure equalization can be life-threatening.
Conditions Affecting Respiratory Function
Disorders of the lungs and airways are serious contraindications because they increase the risk of pulmonary barotrauma, or lung overexpansion injury. This injury occurs when trapped air expands rapidly during ascent, potentially rupturing lung tissue and allowing gas bubbles to enter the bloodstream, leading to an arterial gas embolism (AGE).
Conditions like Chronic Obstructive Pulmonary Disease (COPD), including emphysema and chronic bronchitis, are generally absolute contraindications. They involve permanent air-trapping structures such as bullae or cysts that prevent the smooth release of expanding air upon ascent, making pulmonary rupture highly likely. A history of spontaneous pneumothorax, or collapsed lung, typically disqualifies a diver unless it has been surgically corrected and is associated with normal lung function.
Asthma is the most common respiratory condition evaluated, and its severity is the determining factor. Exercise-induced or severe, uncontrolled asthma is a major concern, as an attack underwater could lead to bronchospasm and subsequent air trapping. Even mild asthma can be dangerous if it causes air to be trapped during an emergency ascent.
Cardiovascular System Contraindications
The underwater environment places unique stresses on the cardiovascular system. Diving involves physical exertion, cold exposure, and a central shift of blood volume, all of which increase the heart’s workload. These factors increase the risk of a sudden cardiac event, such as a heart attack or a serious arrhythmia, resulting in immediate incapacitation and probable drowning.
Conditions like untreated coronary artery disease, recent myocardial infarction, and significant valvular issues such as severe aortic stenosis are absolute contraindications. Aortic stenosis restricts blood flow and can lead to sudden cardiac death under the stress of exercise. Uncontrolled severe hypertension must also be managed and stable before diving, as the physical and emotional stress can dangerously elevate blood pressure.
A specific concern is the Patent Foramen Ovale (PFO), a small opening between the upper chambers of the heart. While an incidental PFO is not an automatic contraindication, it increases the risk of neurological decompression sickness (DCS). The PFO allows venous bubbles, normally filtered by the lungs, to cross into the arterial circulation, potentially traveling to the brain and causing a stroke-like injury. Divers with a known PFO are often advised to follow more conservative dive profiles to minimize this risk.
Neurological and Mental Health Limitations
Any medical condition that can cause a sudden loss of consciousness, impair judgment, or induce panic is a serious limitation due to the high risk of a fatal accident. Epilepsy and a history of seizures are typically contraindications because a seizure underwater would lead to a loss of the regulator and drowning. Even in cases of well-controlled epilepsy, diving presents physiological triggers that can lower the seizure threshold, including oxygen toxicity and nitrogen narcosis.
Most guidelines require an individual with a history of seizures to be seizure-free for three to five years and often off all anti-epileptic medication before diving is considered. Other conditions affecting the central nervous system, such as a recent stroke or Transient Ischemic Attack (TIA), may also disqualify a diver due to the risk of residual cognitive or motor deficits. A neurological examination is a standard part of a dive medical assessment to ensure normal coordination and balance.
Mental health conditions, particularly those involving panic or severe anxiety, also pose significant safety risks. Panic is a major contributor to diving accidents, as a sudden surge of fear can cause a diver to bolt to the surface, leading to pulmonary barotrauma. Panic disorders that impair a diver’s ability to handle stress are serious concerns. Individuals taking certain psychotropic medications must also be evaluated, as the drug’s effects underwater, potentially combined with nitrogen narcosis, are often unpredictable.
Risks Related to Pressure Equalization
The ability to equalize pressure in air-filled body cavities is fundamental to safe diving. Conditions that prevent this equalization can cause barotrauma to the ears and sinuses. Failure to equalize pressure during descent can cause middle ear barotrauma, ranging from pain and fluid accumulation to a ruptured eardrum.
A perforated eardrum is a direct contraindication, as it allows cold water to enter the middle ear, causing severe vertigo and vomiting, which is a life-threatening state of disorientation. Recent ear surgery, such as a stapedectomy, or conditions like Meniere’s disease, which causes balance issues, are high-risk factors. Even a common cold, severe sinus congestion, or an infection can temporarily disqualify a diver because blocked Eustachian tubes or sinus passages prevent pressure clearing.
Forceful attempts to equalize against blocked passages can transmit pressure to the inner ear, potentially rupturing the delicate round or oval windows. This inner ear barotrauma can cause permanent hearing loss, tinnitus, and vertigo. Chronic sinus disease or nasal polyps can also interfere with pressure equalization, leading to sinus barotrauma, which involves pain and bleeding in the sinus cavities.