Diving medicine

Diving remains the principal means of exploring and exploiting shallower underwater zones. Immersion and rapid increase in pressure with depth cause most problems unique to diving.

Effects of pressure on gases and ventilation

Gas density, partial pressures, and solubility vary proportionately with ambient pressure. At elevated partial pressure, nitrogen becomes narcotic, as can other inert gases, and contaminants barely detectable at the surface can become toxic as their partial pressures rise with depth. Hyperoxia irritates the lungs and the central nervous system, and sometimes causing generalized seizures. A safe gas mixture at depth can become hypoxic as the partial pressure of oxygen decreases during the return to surface.

Ventilatory effort is impaired at depth and failure of CO₂ elimination increasingly limits activity. Some divers are not distressed by elevated CO₂, but this does not protect them from its toxic effects.

Clinical problems associated with diving and fitness to dive

Immersion hazards include drowning (Chapter 9.5.3), aquatic flora and fauna (Chapters 9.2 and 9.3), water movement, impaired visibility and thermal control (Chapters 9.5.1 and 9.5.2), and enhanced sound and blast propagation. Immersion predisposes susceptible individuals to pulmonary oedema. Aspiration of seawater can cause pulmonary inflammation and systemic manifestations. Water entering the external auditory meati can induce disabling caloric vertigo.

Decompression illness (DCI)—caused during ascent from a dive by bubbles of inert gas, released from tissues or forced intravascularly by pulmonary rupture. Typical symptoms include limb pain and neurological symptoms (often numbness and paraesthesiae, also disturbance of higher cerebral function which can impair the diver’s insight). Symptoms develop within a few minutes to 24 h of surfacing in most cases. Management requires exclusion of other diagnoses without delaying first aid treatment of DCI with oxygen (as close to 100% as possible) and rehydration, followed by definitive recompression. Intracardiac right–left shunts, such as patent foramen ovale, predispose to the condition. Extracardiac (pulmonary) shunts can also permit a similar paradoxical embolization of bubbles.

Barotrauma—gas-filled spaces within, or surrounding, the body will be damaged unless they are flexible enough to accommodate pressure-mediated changes in volume, or they are ventilated to prevent distortion. Divers’ ears, sinuses, lungs, carious teeth, or their masks and suits are vulnerable.

Long-term consequences of diving—these include aseptic bone infarcts, impaired higher cerebral function, and hearing loss.

Fitness to dive—unrestricted diving demands a high level of physical and medical fitness. Potential disqualifying factors include conditions that might incapacitate, impair, or distract a diver; predispose to DCI or barotraumas; or mimic DCI.