Decompression sickness (DCS) is caused by bubbles in the body. However, there are instances when people with bubbles may not have DCS. Information about bubbles and their effects on divers are presented.

Bubbles in the body cause decompression sickness. What causes bubbles? Is there more to bubble formation and growth than you learned during basic training? What’s the best way to prevent bubbles? Are all bubbles bad? What should you do if you have bubble trouble? Test your knowledge.

  1. True or false. It is common for divers to have bubbles in the body and be without symptoms of decompression sickness.

* A. True

* B. False

  1. Select all correct answers. Gases that diffuse into bubbles inside the human body include:

* A. Nitrogen

* B. Oxygen

* C. Carbon dioxide

* D. Water vapor

  1. Select the incorrect answer. Bubbles form inside divers as a result of:

* A. Tribonucleation

* B. Cavitation

* C. Pressure reduction

* D. Negative pressure areas

  1. True or false. The capillary beds of the lungs are effective bubble traps.

* A. True

* B. False

  1. True or false. Bubbles can form in any tissue in the body.

* A. True

* B. False

  1. True or false. A heart defect can allow venous bubbles to pass directly into arterial circulation.

* A. True

* B. False

  1. True or false. Above water body positioning of a diver suffering decompression sickness affects the location of bubbles inside the body.

* A. True

* B. False

  1. True or false. Gas nuclei (microscopic gas spaces) is an advanced term for bubbles. The nuclei respond to pressure changes the same as bubbles.

* A. True

* B. False

  1. True or false. The surface tension of a bubble is inversely proportional to the radius of the bubble.

* A. True

* B. False

  1. True or False. Bubble growth during decompression sickness occurs because nitrogen supersaturated in tissues diffuses into bubbles and causes them to expand.

* A. True

* B. False

  1. When a tissue eliminates excess nitrogen, a bubble formed in the tissue will disappear after:

* A. Hours

* B. Days

* C. Weeks

* D. Any of the above

  1. True or false. The primary purpose of recompression for the treatment of decompression sickness is to reduce bubble diameter in tissues.

* A. True

* B. False

  1. Whether or not bubble growth occurs during decompression depends on a change in bubble radius as small as:

* A. 1 percent

* B. 5 percent

* C. 8 percent

* D. 10 percent

  1. The best method to prevent bubble formation and growth during decompression is:

* A. A long, slow, vertical ascent

* B. A slow, vertical ascent with a precautionary decompression stop

* C. A long, slow, diagonal ascent

* D. A slow ascent with a two minute stop every ten feet

  1. Breathing oxygen after a dive:

* A. Helps prevent bubble growth and can decrease bubble size

* B. Can relieve symptoms of decompression sickness

* C. Can eliminate the need for medical evaluation

* D. A and B are correct but C is incorrect

Answers: Bubbles

  1. A. True. When you have decompression sickness (DCS), you have bubbles in the body but you can have bubbles without having DCS. Bubbles without DCS are silent or asymptomatic. Bubble growth is a far greater problem than bubble formation.
  2. A, B, C, D. The primary gas inside a bubble is nitrogen, provided a diver breathes air. All gases present in tissues diffuse into a bubble. The greater the partial pressure difference between the tissue gas and the pressure inside a bubble, the greater the rate of gas diffusion into a bubble.
  3. C. Pressure reduction. Believe it or not, the cause of bubble formation that most divers learn about during entry level training is not the cause of bubble formation during decompression! It requires 100 to 200 atmospheres of pressure change to form a gas bubble in a pure liquid. Tribonucleation is negative pressure resulting from the movement of surfaces. Muscle activity also can cause negative pressure. Cavitation is a vortex (cavity or vacuum) formed by moving fluids.
  4. A. True. Venous blood returns to the right side of the heart, which pumps blood that may include bubbles to the lungs. Tiny capillaries in the lungs trap and hold the bubbles until they disappear. Large quantities of bubbles in the blood can overwhelm the lungs, bypass the capillary beds and cause severe DCS.
  5. A. True. Bubbles can form in blood, muscles, ligaments, tendons, fat, organs, the spinal column and all body tissues. Where bubbles form determines DCS symptoms and the rapidity of its onset.
  6. A. True. A fetus has a hole that shunts blood from one side of the heart to the other, bypassing the lungs until birth. A flap of skin is supposed to cover the hole at birth and grow shut. If the hole does not close, a person has a Patent Foramen Ovale (PFO). Such a condition in a diver predisposes the person to DCS because bubbles bypass the lungs and cross directly into arterial circulation.
  7. B. False. Experts now realize the idea of body positioning affecting bubbles in circulation is largely without merit. Medical experts discourage the long held practice of placing injured divers in a head-down position. The theory was that gravity would affect bubbles but it is easy to demonstrate the concept is incorrect. Watch what happens to bubbles inside a hose that contains moving water. The bubbles move with the water no matter how you position the hose.
  8. B. False. Gas nuclei (also called bubble seeds) are different than bubbles (also called gas phase). How? Gas nuclei do not respond to Boyle’s Law. A bubble increases its size with any decrease in pressure. A gas nuclei can become a bubble but, until it does, it behaves differently.
  9. A. True. The “skin” of a bubble has cohesion that holds it together. The cohesive, bonding force is surface tension. The smaller the bubble, the greater the surface tension. As a bubble grows or expands, the surface tension decreases at a rate inversely proportional to the bubble radius. Surface tension can exclude gases until bubble diameter reaches a critical size. Surface tension gas exclusion helps explain why bubbles in the body can be asymptomatic. Surface tension keeps the bubbles from growing.
  10. A. True. During decompression, tissue nitrogen pressure reaches supersaturation (pressure greater than the surrounding pressure). If the gas pressure is greater than bubble surface tension, nitrogen diffuses into the bubble, increasing bubble size and decreasing surface tension. At a critical crossover point supersaturation triggers rapid bubble growth and DCS.
  11. D. Any of the above. Several factors affect bubble behavior: Pressure increases or decreases, ambient (surrounding) gas pressures, perfusion (tissue circulation) and bubble size. The problem is that bubbles damage host tissues. It is far better to prevent bubble growth in body tissues than to treat DCS.
  12. B. False. Pressure does reduce bubble diameter and helps relieve symptoms but not as much as many divers believe. When you double the pressure on a bubble, its relative diameter decreases only 21 percent. To decrease bubble diameter by half, the required pressure equals a depth of 231 feet! Recompression retards bubble growth while oxygen breathing shrinks bubble size.
  13. A. 1 percent. According to a paper by Dr. Hugh Van Liew of the University of Buffalo, New York, “…an increase of less than 1 percent changed the situation from no-growth to growth…and the growth caused a rapid decrease of surface tension pressure. The nucleus became a bubble.” Dr. Van Liew’s findings help us understand why DCS is so unpredictable.
  14. C. A long, slow, diagonal ascent. The prevention of bubble formation during vertical ascents can require decreasing the ascent rate by a factor of ten. According to Dr. Van Liew, “An alternative to two-stage decompression is a slow linear ascent that allows a diver to arrive at the surface in the same time but without stops…the slowest possible ascent is desirable.”
  15. D. A and B are correct but C is incorrect. Breathing oxygen after a dive can help prevent bubble growth and may relieve symptoms of decompression illness but the injured diver must always receive medical evaluation. Dramatic recoveries are possible with oxygen first aid but it is not adequate treatment for a diving injury.

The quiz tests advanced level knowledge, so don’t be troubled if you did not do well. If you learned about bubbles, that is more important than how many questions you answered correctly. The most important aspect of bubble knowledge is how you apply it. Incorporate the principles and recommendations of the quiz and a void bubbles as much as possible.


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