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CHAPTER 3 — Underwater Physiology and Diving Disorders 3-23 3-6 MECHANICAL EFFECTS OF PRESSURE ON THE HUMAN BODY-BAROTRAUMA DURING DESCENT Barotrauma, or damage to body tissues from the mechanical effects of pressure, results when pressure differentials between body cavities and the hydrostatic pres­ sure surrounding the body, or between the body and the diving equipment, are not equalized properly. Barotrauma most frequently occurs during descent, but may also occur during ascent. Barotrauma on descent is called squeeze. Barotrauma on ascent is called reverse squeeze. 3-6.1 Prerequisites for Squeeze. For squeeze to occur during descent the following five conditions must be met: n There must be a gas ­ filled space. Any gas ­ filled space within the body (such as a sinus cavity) or next to the body (such as a face mask) can damage the body tissues when the gas volume changes because of increased pressure. n The gas ­ filled space must have rigid walls. If the walls are collapsible like a balloon, no damage will be done by compression. n The gas ­ filled space must be enclosed. If gas or liquid can freely enter the space as the gas volume changes, no damage will occur. n The space must have lining membrane with an arterial blood supply and venous drainage that penetrates the space from the outside. This allows blood to be forced into the space to compensate for the change in pressure. Incus Semicircular Canals Vestibular Nerve Facial Nerve Cochlear Nerve Cochlea Round Window Eustachian Tubes Stapes at Oval Window Malleus Tympanic Membrane External Auditory Canal Figure 3-7. Gross Anatomy of the Ear in Frontal Section.

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