The process of drowning is well-described by survivors and follows a consistent pattern. Of course, the panic and severe psychological trauma continues until lost consciousness.
Superimposed upon the continued extreme panic, the physically painful effects began and rapidly increased during this phase of drowning. At first during a drowning, there is a period of “breath holding” technically known as voluntary apnea. Normally, a person can hold their breath for a reasonably comfortable period of approximately 15-30 seconds before the drive to breathe causes them to voluntarily take a breath. Most people have tried to hold their breath for as long as they can beyond the comfortable period, and this increasingly painful feeling is well-known. The physiological underpinning of this phenomenon is the buildup of carbon dioxide in the blood. The brain is intensely sensitive to elevated levels of carbon dioxide which is normally exhaled during breathing. Buildup of carbon dioxide leads to acidification of the blood. Carbon dioxide levels are, in fact, much more important and powerful drivers of breathing than oxygen levels.
While underwater, the normal period of voluntary apnea under nonstressed situations becomes longer because of an innate drive to not inhale water. This instinct is so powerful that the drive to exhale carbon dioxide becomes secondary. People in drowning situations can maintain voluntary apnea well beyond the normal time frame in spite of increasing terror and physical pain. It has been documented that 60 to 100 seconds of voluntary apnea can be maintained underwater without training or pre-planning. With training, people can maintain apnea for much longer, with expert swimmers lasting up to several minutes. In extreme examples, expert deep divers have been documented to maintain apnea for over 20 minutes with antecedent hyperventilation.
Drowning is a type of asphyxia. The physical pain of drowning increases constantly throughout the period of apnea, during which the body is responding to the ongoing steady increase of carbon dioxide and acidity of the blood. The earliest physiologic manifestations compound the underlying sensation of panic. In addition, the victim experiences chest pain which increases in severity until the end. This has been described as a tearing or burning sensation, as if their lungs had been set on fire. As well, chest muscles begin to ache.
The final physiological event is the point at which the carbon dioxide levels become so high that an involuntary breath is inevitable regardless of being underwater. When that first reflexive breath occurs, the victim is still conscious though drowning becomes all but inevitable. A sharp, spasmodic breath sucks water into the mouth and the foreign fluid strikes the pharynx and airways. This results in extreme choking and gagging sensation, with airways completely blocked off, no possible source of oxygen, and a severe noxious stinging and burning sensation in the nose and airway. Anyone who has accidentally had water forced up the nose or mouth while swimming or diving can attest to a very minor degree of the severe painful sensation one experiences while actually drowning.
As a result of that breath, in most cases, water enters the lungs and completely shuts down any possibility of lung function. The water in the lungs has low concentrations of electrolytes so, by diffusion, fluid passes nearly immediately into the blood vessels. This rapidly causes severe electrolyte disturbances. In a minority of cases, referred to as “dry drowning,” the water hitting the larynx causes spasm of the larynx and blocks water from entering the airway. The sensations of dry drowning are the same as the more typical “wet” drowning, but at autopsy we do not find fluid in the lungs. In either case, the end result is the same. Within several seconds of this final period of agony, brain function shuts down with a typical sensation of “blacking out” paired with the knowledge of imminent death. Brain death actually occurs approximately 4 to 6 minutes after loss of consciousness, followed thereafter by cardiac death; the patient may be rescued prior to that final endpoint and may survive but with long term consequences.
The process of drowning medical expert witness specialties include forensic pathology.