Barotrauma is an injury caused by pressure change in a cavity, and is a common fatality among divers. An example of such injury is to the middle ear or sinuses.
As a diver descends into deeper waters, external pressure against the whole surface of the body, including the insides of the ears and sinuses, is increased. Divers regularly need to equalise the pressure by means of a valsalva manoeuvre. This is done by pinching the nose while the mouth is closed and trying to exhale. This pushes air up the Eustachian tube to equalise the pressure on both sides of the ear-drum. If this is not done, the outside water pressure will rupture the eardrum and cause immediate pain.
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Equalising is important
On ascent, the reverse will follow, with gas inside the cavity needing to escape with the decrease in external pressure. The gas will bubble out of the Eustachian tube spontaneously. A diver can assist the process by simply swallowing, also known as 'popping the ears'.
Another example of barotrauma is if a diver ascends to the surface too rapidly without exhaling adequately. With the decrease in pressure against the body, compressed air in the lungs will begin to expand. If the diver holds his/her breath, or does not breathe correctly, the tissue lining and cell walls will stretch, leading to a rupture at the weakest point. Air will escape directly into the bloodstream, causing bubbles to flow directly through the heart and brain, causing unconsciousness, and even possibly death. This is known as Pulmonary Over Pressurisation Syndrome (POP) and Arterial Gas Embolism (AGE).
More about pressure
The human body is designed to withstand an average 6.7kg per 6,5 square centimetres, the pressure at sea level. If the same area of water and air were compared, water weighs far more than air does. Therefore, water pressure on your body is far higher than the equivalent to that of air pressure.
Forty metres is the recommended depth to which divers should go. The pressure at this level is the equivalent to five atmospheres (approximately 90 tons of pressure).
(Health24, June 2006)
Source: Jos Beer, Safety and Training Manager, Cape Diving (Pty) Limited
Source: Dr Jonathan Rosenthal, Hyperbaric Physician, Diving Medical Examiner
Source: Last Breath, Cautionary Tales from the Limits of Human Endurance, Peter Stark, Chapter 9, Bubbling from the Bottom Up, The Bends
Reviewed by Dr Jonathan Rosenthal, Hyperbaric Physician, Diving Medical Examiner
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