NAUI Master Scuba Diver 120 Diving Physiology toes back. Stretch a quadriceps cramp in the front of your leg by bending your leg at the knee. Occasionally, a twinge of the unhappy muscle will give you an early warning. Stop and stretch the muscle to prevent a full locking contraction. Do not ignore a cramp. A cramped muscle becomes more likely to remain in painful spasm the longer it is allowed to cramp. Prevention: Proper kicking is your main prevention for leg and foot cramps. Kick with loose, floppy ankles. Do not “hold” your ankles - there is no motor control of the foot in a good kick. Allow your ankles and feet to flop whichever way the water moves them. Don’t curl or hook your toes. Don’t lock your knees. Maintain good physical fitness, good nutrition and health, swim regularly with fins, regularly stretch your legs to keep them flexible and mobile, use properly fitting fins, and adequate thermal protection. Carotid Sinus Reflex The main arteries carrying blood up to your brain are your carotid arteries, on either side of your neck. At the main fork in each carotid artery there is a small bulge called a sinus. The word sinus does not only mean the air-filled cavities in your head that get stuffy; sinus refers to various small hollows or channels in your body. Your carotid sinus contains baroreceptors, which are receptors that sense changes in blood pressure (figure 4-9). When your baroreceptors sense that your blood pressure is too high, they send a reflex signal to slow your heart and enlarge your blood vessels, which drops your blood pressure. It is normally a good, well-working system to keep things even for you, and part of your larger network of blood pressure regulating systems. However, you can fool your carotid sinus baroreceptors with a tight hood or neck seal, or just by pressing the sides of your neck. Your baroreceptors think that high blood pressure is pushing on them. In response, they send signals to lower your heart rate and blood pressure. The carotid sinus reflex is used in medicine for patients having an acute attack of high blood pressure or rapid heart rate. Rubbing the carotid sinuses on both sides, called carotid massage, slows heart rate and drops blood pressure. Physicians are cautioned when Heart Carotid artery FIGURE 4-9. CAROTID SINUS REFLEX. examining an elderly patient not to palpate both sides of the neck at once to avoid inadvertently invoking the carotid sinus reflex. Effects: The word carotid comes from a Greek word meaning “to stupefy” or “put to sleep.” If you compress your carotid arteries too much, you can make yourself dizzy or lightheaded, even unconscious, particularly when you are exerting yourself. First Aid: Stop the pressure. If you are dizzy on land, bend over immediately or lie down so that gravity can bring blood back to your head. If you are dizzy under water due to a carotid sinus effect, loosen whatever is pressing on your neck, stop exertion, and signal your buddy to monitor you on the way up. Prevention: Choose an exposure suit that does not fit too tightly around your neck. Dry suit neck seals can be tight. Wet suit jackets may zip up high enough to be constricting, either by themselves or when zipped over your hood. When choosing a hood, try it on with your wetsuit. A hood that is not too tight may become too tight under a zipped up jacket. Choose a well-fitting buoyancy compensator that does not ride up when you are on the surface and compress your neck.
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