Problems Of Descent

One of the most far reaching and oft experienced laws of physics encountered by divers is Boyles Law, which states, essentially, that under conditions of constant temperature, pressure and volume of gases are inversely proportional. This means that as you increase the pressure applied to a flexible container, the volume of that container is decreased. For instance, visualize a balloon inflated at the surface and then taken underwater. As the balloon is taken deeper the pressure upon it increases and the size of the balloon decreases. What is happening, of course, is that the water pressure outside the balloon is compressing the balloon, and the air inside it, until the air pressure inside is equal to the water pressure outside.

As the balloon is brought toward the surface, the water pressure outside is lessened because of lessening depth and the balloon begins to grow in size, or volume again, until, at the surface it is again its original size or volume.

As Boyles Law affects the human body, its importance is immediately obvious. For instance, the middle ear is a natural air space in the body, with a flexible wall exposed directly to outside pressure. (The eardrum). When a diver descends from the surface to a depth underwater, the air inside the middle ear is at surface pressure. As his depth increases, surrounding or ambient pressure increases. In accordance with Boyles Law, the eardrum bows inward, thus reducing the volume of the middle ear, and causing considerable pain in the process. If the outside pressure is increased enough and the air pressure inside the middle ear is not raised to equal it, the result will be a bowing inward of the eardrum until it can bow no further, but instead implodes or ruptures inward. When this occurs, cold water rushes into the middle ear, creating dizziness, confusion, and a loss of balance. Often this bursting of an eardrum underwater creates a condition known as vertigo, which is a combination of all the symptoms. If the diver will remain stationary and wait a few minutes, the condition will correct itself as the body becomes accustomed to the new condition. However, there is a serious possibility of infection and the ruptured ear should receive treatment by a physician.

The sinuses are also connected to the respiratory system, and are filled with air. If the opening or passage to the sinuses is closed for any reason, the walls of these structures being composed of tissue, will attempt to bow inward until the cell walls rupture and the structures attempt to equalize the pressure by partially filling the cavity with blood.

The obvious means of preventing these mishaps is for the diver to forcibly equalize the air pressure in these natural air spaces. If, for instance, the diver holds his nose and blows, he will force air, under pressure, into the middle ear, via the connecting eustachian tubes. If these tubes are blocked by mucus or other matter, clearing of the ears is impossible, and the diver should not attempt to descend. The same applies to the sinuses. Very often, even though the diver has apparently been successful in clearing, or equalizing as he descended, he will experience a slight nose bleed upon surfacing. This means that he was unable to equalize his sinuses completely, and that some of the minor capillaries have ruptured. As long as the bleeding is minor, and stops soon after surfacing, it is unimportant. However, if nosebleed persists, or is profuse, medical attention should be procured without delay.

SHADED AREAS SHOWING SINUSES

Another type of squeeze, which is of very grave importance to the skin diver, is thoracic, or lung squeeze. Here, as the diver descends holding his breath, the ambient pressure increases and the volume of the lung decreases until a point is reached where the lungs collapse and the thoracic cavity begins to fill with blood. This is a very often fatal condition and for this reason free dives without scuba should be limited to 100 feet.

When the diver is wearing scuba, these squeezes, or pressure differentials still plague him. The basic premise of scuba is that the diver is always breathing air at surrounding pressure, thus, if he is able to equalize the pressure throughout his body he has no squeeze problem. However, as mentioned before, these passages of the natural air spaces are often blocked by mucus or other matter, and then equalization becomes a matter of concentrated effort. In the case of the ears, equalization can usually be effected by merely swallowing, which causes the eustachian tubes and the passages to the sinuses to gape open, facilitating the equalization of pressure. However, the presence of a slight amount of mucus can block these passages and it may become necessary for the diver to forcibly clear. This is done by either blocking off the nostrils through the mask or taking the mask off and holding the nose and then trying to blow through the nostrils. The ears will clear with a noticeable popping or squeaking, if at all. If it is not possible to clear the ears at this level, the diver should ascend a few feet and try again. If the ears will not clear, the diver should not attempt to descend, but would be far wiser to leave the water, to try another day. For best results, the diver should clear his ears every four feet of descent, rather than wait for the pressure differential to become uncomfortable. By clearing often, irritation of the eustachian tube opening is avoided and equalizing is facilitated.

There are on the market today many commercial decongestants which are of inestimable value to the diver. However, these should be checked out with a doctor before being used. Any respiratory infection, such as a cold, should keep the diver out of the water, for obvious reasons.

In addition to the air spaces in the respiratory tract, there are also at times air spaces in the digestive tract. These are not of very great importance, except with the use of scuba where, occasionally, air may be swallowed. Upon ascending the air in the digestive tract expands causing a condition known as divers colic. This can be readily relieved by belching or otherwise relieving one's self of excess air pressure.

A brief word should be said about external air spaces attached to the diver. For instance, the face mask worn by the diver contains an air space. If this air space is not equalized with surrounding pressure a squeeze occurs. In mask squeeze the mask tends to flatten against the divers face and the pressure being less than that contained in the divers body (which, in the use of scuba, is equal to ambient pressure) causes the minute capillaries just under the skin and in the eye to rupture, giving the diver the appearance of a sunburned face and bloodshot eyes. The same situation prevails in the use of a dry type exposure suit, when the pressure is not equalized, leaving the body covered with welts.

The mask squeeze can be eliminated very simply, merely by exhaling a small quantity of air into the mask through the nostrils as you descend. As you ascend, a slight inhalation through the nostrils will keep the mask seated. In use of the dry suit, it is necessary to exhale into the suit from time to time to pressurize it. However, it should be remembered that this air must be vented upon ascent, or the suit will balloon, and may bring the diver up to the surface feet first, to dangle there helplessly

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