Chapter 4- Diving Physiology Diving Physiology 135 Enter and exit along a line if visibility is poor. Vertigo Vertigo is often imprecisely used as a general term for dizziness. More specifically, it means a hallucination of spinning, rotation, or whirling. Vertigo can occur from problems with your vestibular system or brain. You can get vertigo from hyperventilation, using alcohol or drugs, from motion sickness, even high places if you have a fear of heights. In diving, vertigo can result from inner ear DCS, covered earlier in “Decompression Sickness,” and from unequal stimulation of your ears by temperature or pressure. Vertigo from temperature may result if you break an ear drum from forcing or failing equalization. Cold water rushes into one middle ear. Or more simply, cold water enters one external ear canal and not the other because one side is covered by your hood or filled with ear wax. Your vestibular system on one side cools, producing sudden and sometimes intense vertigo. Vertigo from pressure can result if you damage your vestibular apparatus by excessive force during ear clearing. Or more simply, you equalize one ear but the other ear is too stuffed up to equalize. The unequal pressure in either case can produce vertigo. This is more pronounced if pressure change is sudden. Pressure building up in your ear during ascent (reverse block) can produce alternobaric vertigo. Effects: Whirling sensations. May produce headache or nausea. First Aid: Stop and grasp a stationary object for reference. Wait for the dizziness or whirling to pass. If vertigo occurs in mid-water where there is nothing to grasp, hug yourself. The value of a nearby buddy in such instances is apparent. If problems persists, stop diving and get medical assistance. Prevention: Practice good equalization early and often. Descend feet first. Maintain good health. Don’t use alcohol or recreational drugs before diving. Get regular checkups. Dehydration Dehydration is abnormal loss of water from your body that you do not replace. It does not mean any water loss. You normally lose water all day and all night in several ways as part of your body’s normal heating, cooling, humidifying, and cleaning systems. Overheating during diving preparation can increase your sweating. Both immersion and cold stimulate your body to urinate more than usual, a response called increased diuresis. Scuba air is dry. With each breath through your regulator, your body uses water to humidify the air. None of these, by themselves, is a problem. When you increase water loss through one avenue, your body helpfully reduces water loss another way. For example, when you exercise and sweat more, you urinate less. Losing water is not a problem as long as you replace what you lose. Dehydration results when you lose more than you replace. Effects: Dehydration greatly reduces your tolerance to heat and ability to exercise. You fatigue early. Your heart rate increases, and your mouth may feel dry. You may even be thirsty. Dehydration is thought to predispose you to other diving problems, particularly decompression sickness. First Aid: Stop, rest, remove yourself from the heat, and drink nonalcoholic, noncaffeinated fluids. Sport drinks replace fluids, minerals, and salts that you need, and stimulate your thirst so that you will drink more. Sport drinks work best undiluted, and there is no physiologic need to dilute them unless you prefer the taste that way. Prevention: Drink fluids before and between dives. Drink before you feel thirsty. Get into good aerobic condition. Higher physical fitness increases the total circulating fluid volume in your body, better preparing you for activity in the heat. With greater volume, you have enough blood to distribute to your skin for cooling and also enough fluid volume for sweating. Good aerobic condition is your most important factor in tolerating exercise in the heat. Don’t overdo drinking water. You can drink so much water that you dilute yourself too much. Overdilution is not common, but for people who drink only large quantities of water without eating
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