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Squeezes When you descend, the pressure on your body increases at a rate of about 0.1 bar per meter or about 0.5 psi per foot of depth. If any air space in your body is closed off so that the pressure inside the air space cannot stay equal to the surrounding pressure, the surrounding pressure tries to compress the air in the air space. Whenever the pressure outside an air space is greater than the pressure inside an air space, the situation is called a squeeze and it can cause damage to your body. Doctors also call this type of injury a barotrauma, which means pressure injury. Divers can experience many different types of squeeze. You must be specific when you discuss this type of condition. For example, you can get squeezes in your sinuses, middle ear, or mask. You can avoid each of these squeezes by using proper equalization techniques. Blocks A reverse block is the opposite of a squeeze. It occurs when the pressure inside an air space is greater than the surrounding pressure. Blocks can occur during ascent. Air is trapped inside an air space and the air tries to expand as the surrounding pressure decreases. Middle Ear Chapter 4- Diving Science The air spaces inside your middle ears are especially important when you dive. You must be able to equalize the pressure inside your ears to comfortably and safely dive. Anatomy Your ears are divided into three sections: the outer ear, the middle ear, and the inner ear (figure 4-21). The outer ear is your ear canal. The eardrum separates your outer ear from your middle ear. The eardrum is a flexible membrane that vibrates when sound waves hit it. Your middle ear contains a series of three small bones that transmit sound waves from the eardrum to the inner ear. Your middle ear also has an airway linking it to the back of your throat. This airway is called the Eustachian tube. Your middle ear transmits sound waves from your eardrum to the auditory nerves of your inner ear. Your body’s balance mechanism is also contained in the inner ear. If you have a sudden change in pressure or temperature in one ear and not the other, you can get dizzy or experience vertigo. Middle Ear Squeezes A middle ear squeeze occurs when the air or water pressure in your outer ear is greater than the air pressure in your middle ear. You equalize your middle ear by moving air from your throat through the Eustachian tube into your middle ear. For most people, equalizing the pressure inside their ears is not an automatic process. To pass air through the Eustachian tubes usually requires a deliberate action to open the tubes and allow air to flow through them. If you cannot equalize your ears during a dive, you must end the dive and return to the surface. As you descend in the water, the pressure on your outer ear increases and pushes in on the eardrum. If the pressure continues to increase and is not equalized in the middle ear by passing air through the Eustachian tube, pain will be felt; and the eardrum flexes in to help equalize the pressure. Finally, the eardrum can rupture Diving Science 107 FIGURE 4-20. THE AIR SPACES IN YOUR BODY INCLUDE YOUR LUNGS, SINUSES, AND MIDDLE EARS. YOU CAN ALSO HAVE AIR SPACES IN YOUR STOMACH, INTESTINES, AND TEETH.


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