The following is from an article in the fall 1986 issue of the National Aquatics Journal. The author, Dr. Alison Osinski, is assistant professor of physical education at San Diego State University. She says that about 90 percent of freshwater drownings occur in this way and that 10 percent happen in a supervised pool with lifeguards on duty.
An individual finds himself unexpectedly in the water. Unable to save himself because of lack of swimming ability or injury, and unable to summon assistance which should be readily and immediately available, he panics, struggles briefly on the surface of the water and then slips below.
After submerging, he holds his breath until no longer able. He eventually resigns himself to the fact that he is going to drown, and a sense of calm overtakes him. As he begins to lose consciousness from asphyxia, the reflex closure of his glottis is overcome by the need to breathe. He inhales a large quantity of water, then begins to vomit.
The regurgitated water and vomit are aspirated into his lungs. As he begins to sink deeper in the pool, the increased water pressure on his chest forces the remaining air out of his lungs. The water now in his lungs passes into his bloodstream and dilutes the blood. As the salt concentration of his blood is lowered, the red blood cells begin to burst into the surrounding plasma and be destroyed. The hemolysis causes a frothy pink fluid to build up in his lungs and a tremendous swelling to take place. An electrolyte imbalance develops as calcium levels decrease because of the blood dilution, and potassium levels increase as a result of the breakup of red blood cells.
In the wake of this electrolyte imbalance and oxygen deprivation, his heart is forced into ventricular fibrillation. Within a short time, he is clinically dead.