The cardiovascular system undergoes changes underwater. By being aware of the changes and knowing why they occur, divers can better understand what happens to them. Knowledge of the effects on circulation underwater can also help prevent injury and accidents.

1. The likelihood of a heart attack is no greater while diving than when exercising on land.

A. True
B. False

2. The amount of oxygen carried in the blood increases significantly with increased exercise.

A. True
B. False

3. Pressure on the neck, such as that from a tight hood, causes the heart rate to increase.

A. True
B. False

4. The diving reflex causes changes in circulation. The degree of response is determined primarily by the temperature of the water.

A. True
B. False

5. Blood pressure is lower underwater than on land.

A. True
B. False

6. Blood is shunted from extremities to conserve heat in the core of the body. This remains true no matter how cold the extremities become.

A. True
B. False

7. When blood is shunted from extremities to conserve heat, one result is increased urination (diuresis).

A. True
B. False

8. Alcohol increases circulation to the skin and increases heat loss.

A. True
B. False

9. Under pressure, enough oxygen can be carried by the blood plasma to meet the body’s needs even if the oxygen carrying capability of blood hemoglobin has been significantly reduced.

A. True
B. False

10. With frequent exposure, it is possible to improve vasoconstriction and, therefore, tolerance to cold water.

A. True
B. False

11. Owing to the many effects on circulation caused by submersion, medical experts have determined that diving is unhealthful for the average person.

A. True
B. False

Answers: Circulation

1. A. True. The blood supply to the heart, efficiency of its muscle contractions, changes in rate and rhythm and increased work load all result from diving. Such stresses can be tolerated by a healthy heart, but can cause a heart attack in those with coronary problems. A person with any heart disorder should not dive unless cleared by both a cardiologist and a diving physician.

2. B. False. The blood carries nearly as much oxygen as it can at all times. The change that takes place with exercise is in the circulation of the blood, which is increased to get oxygen to and waste products from tissues more quickly. Increased oxygen partial pressure while diving does allow more oxygen to be carried dissolved in the blood, but the benefit of this is offset by other cardiovascular changes.

3. B. False. The carotid sinuses, located at the bifurcation of the arteries on each side of the neck, are sensors for blood pressure and provide information to the brain to control heart rate. As pressure increases, the sinuses tell the brain to slow the heart. Artificial pressure, such as a tight hood, also results in slowing of the heart. This can be dangerous, can lead to blackout and must be avoided.

4. A. True. The diving reflex is much more pronounced in marine mammals than in man, but its effects have been documented and include cardiovascular changes. The controlling factor seems to be the temperature of the water in contact with the face. The colder the water, the greater the effect. It should be noted that the effects of the diving reflex are not always beneficial. Diving in very cold water places quite a strain on the circulatory system.

5. B. False. Rapid loss of body heat can occur in water. To reduce the loss, the body reduces blood flow to the skin and extremities. This vasoconstriction results in a greater volume of blood in the torso, increasing blood pressure slightly. Weightlessness in water also reduces the pooling of blood in the legs. Higher blood pressure is not a problem except for those who already have such difficulties.

6. B. False. As explained in the previous answer, vasoconstriction is the body’s defense against heat loss. However, when the skin temperature of an extremity drops below 50|F circulation is pathologically restored to the extremity owing to failure of construction. This is called “cold induced vasodilation,’ is undesirable and is potentially hazardous because the heat lost from the body is very great when the vasodilation occurs. Insulation of the extremities is needed in very cold water to prevent hypothermia.

7. A. True. In cold water, diuresis occurs because the volume of blood in the trunk of the body is increased. This means the blood passes through the kidneys in greater amounts, so the need to urinate is more frequent. Incidentally, the negative pressure breathing of diving is also diuretic. If you feel you urinate excessively when you dive, don’t worry, you are only normal!

8. A. True. Alcohol causes vasodilation, which is just the opposite of the effect created in the body as a reaction to cold. Drinking before diving inhibits the system’s heat loss defense mechanism, while drinking after diving may release nitrogen trapped in cold extremities and contribute to the bends. Teetotaling divers have good justification for their abstention.

9. A. True. Higher partial pressures caused by depth increase the amount of oxygen in the bloodstream. This explains why the effects of carbon monoxide toxicity are experienced during ascent – when the partial pressure of oxygen is decreasing – rather than when the afflicted diver is at depth. If you are not feeling well, be sure to have someone ascend with you because loss of consciousness is quite possible on the way to the surface.

10. A. True. Studies of the Ama divers of Japan have shown this to be true, and I and others I know will also vouch for it. Isn’t it nice to know that the more you dive the more comfortable you will be? This is a great excuse to justify diving on a regular basis.

11. B. False. While diving does require participants to be in good health, the medical community does not suggest that it is harmful for healthy persons. What is known, however, is that those with cardiovascular problems are much more likely to experience difficulty while diving that they would otherwise. A person with circulatory problems should consult a diving physician before diving.

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