Dry drowning

Dry drowning is when a person's lungs become unable to extract oxygen from the air, due primarily to:


 * Muscular paralysis
 * Puncture wound to the torso (affecting ability of diaphragm to create respiratory movement)
 * Changes to the oxygen-absorbing tissues
 * Persistence of laryngospasm when immersed in fluid

The person may effectively drown without any sort of fluid. In cases of dry drowning in which the victim was immersed, very little fluid is aspirated into the lungs. The laryngospasm reflex essentially causes asphyxiation and neurogenic pulmonary oedema.

Dry drowning can occur clinically, or due to illness or accident, or be deliberately (and repeatedly) induced in torture (waterboarding). It can be traumatizing, and it can be deadly

Pathophysiology
The pathophysiology of this form of pulmonary oedema is multifactorial.

In normal breathing, the diaphragm contracts, causing it to drop and increase the volume of the chest. This increase in volume causes a partial vacuum, which draws air into the lungs from the outside. During laryngospasm, the person's larynx spasms shut. As a result, the partial vacuum created by contracting the diaphragm cannot be filled by the inrush of air into the lungs, and the vacuum persists. In an attempt to force air in through the spasmed larynx, the person may contract the diaphragm further, but this only increases the partial vacuum inside the chest.

The heart continues to beat during this time, and blood continues to flow, though it can neither pick up oxygen nor drop off carbon dioxide in the lungs. The volume of blood in the chest can increase, however, by pulling in more blood from the abdomen, head, arms and legs - abnormally large volumes of this blood enter the chest via the superior and inferior vena cavae (great veins) in response to the persistent partial vacuum. From the vena cavae, the increased volume of blood flows through the right atrium and into the right ventricle. The volume of blood is great enough to stretch out the ventricle, similar to water entering a balloon.

The ventricle typically responds to this increased volume of blood by contracting and pumping with increased strength - a phenomenon known as the Frank-Starling mechanism. On being ejected from the right ventricle, the blood is forced into the pulmonary artery and thence to the lungs.

In the lungs, the nature of the vasculature changes. The vessels become extremely narrow - narrow enough that red blood cells have to pass though in single file. The walls of the vasculature also become extremely thin to allow oxygen to enter the blood and carbon dioxide to leave it. In the case of dry drowning, however, there is no oxygen available in the lungs; there is only a partial vacuum. This partial vacuum draws some of the fluid from the vasculature and into the airspaces of the lungs, creating pulmonary oedma.

At the same time, the sympathetic nervous system responds to the emergency of the closed larynx. Among other things, it constricts much of the body's vasculature. This vasoconstriction increases the pressure against which the left ventricle must pump, and may cause enough backpressure to ripple back through the left ventricle, into the left atrium, and into the pulmonary vasculature. This additional pressure on the blood in the lungs' blood vessels exacerbates the oedema described above.

Additionally, the actions of the sympathetic nervous system can damage the lungs' vasculature, allowing even more fluid to escape into the lungs' airspaces.