Salt water aspiration (SWA) is a ubiquitous consequence of diving in the ocean, as well as among surfers, snorkellers, helicopter rescuees and ocean swimmers, who now recognize SWAS.
With divers, a watertight seal of the demand valve should ensure that water does not enter the spaces that carry the inspiratory and expiratory air.
This depends on the integrity of the mouthpiece, inspiratory valve or diaphragm (rubber or silicone) and the expiratory or exhaust valves. Any damage, wear, perforation, displacement or foreign body can disrupt these seals. This is more likely with increasing pressure gradients across the seals, such as with increasing respiration.
Whether the diver is aware of the ‘leaking’ probably depends on many factors, such as the volume, the site of entry (the proximity of the leak to the air inlet) and the attention paid to other activities. Sometimes the diver will recollect a specific incident leading to the aspiration (often inducing a cough), or he or she may notice a ‘bubbling’ or ‘wet’ sensation in the regulator. Other times, the diver may not notice anything, as occurs with the inhalation of many nebulized particles.
SWA in divers may occur in certain circumstances, namely:
- In inexperienced divers because they commonly overbreathe the regulator.
- Excessive respiratory flow and volumes, as with exercise and anxiety.
- Increasing depth and thus density of the inspired gas.
- During buddy breathing or re-inserting the regulator underwater.
- From a faulty, corroded or damaged regulator.
- Foreign body (salt crystals, weed, sand) interference with the diaphragm or exhaust valve seating.
- Failure of the mouthpiece seal, as from tears.
- Being towed at speed.
- With upstream regulator valves, as in some surface supply units.
- Whenever the air intake is below the exhaust outlet – a positional effect.
- Removing the regulator on the surface.
As we know from respiratory medicine, larger volumes of fluid in the upper respiratory tract stimulate a laryngeal response varying from coughing to laryngospasm. Nebulized droplets with diameters of 1 to 10 micrometres are distributed to the terminal bronchi, with less deposition in the upper respiratory tract. The aspiration volumes in diving probably depend on the previously listed 10 circumstances.