Miss RE 12/29/08

The Bends Effect

A. Purpose:

This experiment should demonstrate how a sudden decrease in pressure causes gases dissolved in a liquid to form bubbles. The bubbles in the carbonated water simulate the way blood acts when pressure around it decreases rapidly (as when divers surface quickly). Thus the bottle provides a model of the human blood vessel, and the experiment shows how bubbles form can in divers blood. This bubble formation causes the illness known commonly as the bends.

As humans enter high-pressure environments (the most common example being under water), the air in their lungs (or in their SCUBA tank) is also put under higher pressure. Gases can dissolve into liquids in greater amounts at high pressures than at the typical, sea level pressure of one atmosphere that people experience. As described by natural gas laws, exposure to increasing pressure forces more gas to dissolve in the bodily fluids and tissues of humans as they descend under water (Campbell). This dissolving gas is primarily nitrogen, since nitrogen makes up the greatest percentage of the air humans breathe. Conversely, as divers rise back to the surface, pressure decreases, as does the solubility of the gases in blood and tissues. If the ascent is made too quickly, the gases will come out of solution as bubbles in the circulatory system, blocking blood flow, and in the bones, causing tissue damage.

This process leads to a condition called the bends, officially known as Decompression Illness (DCI). Symptoms range from joint pain and nerve tingling to brain problems and paralysis. Not only can divers contract it, but miners working in pressurized conditions have also been known to fall victim to the bends, and airplanes must be carefully pressurized to avoid this condition. Nitrogen bubbles, particularly those forming in or near joints, are generally thought to cause the joint pain of a classical bend (Thalmann). High concentrations of these bubbles can lead to brain problems and damage to motor systems, for much of humans blood goes to the brain. Almost every part of the body is affected by the bends because of the ubiquitous nature of bubble formation.

This experiment should show how gases dissolved in a pressurized liquid will form bubbles if the pressure decreases suddenly. Initially few or no bubbles should be seen in the unopened bottle. Once the cap is twisted and the bottle opened, however, bubbles should rapidly form. This, then, will simulate the way air bubbles form in blood.

Complete understanding of the bends is scientifically important for human safety and for deeper understanding of marine organisms. Because of the potential lethality of the bends, full knowledge of its causes and effects is very important. Understanding its causes allows divers to avoid the bends or choose effective treatments for them. Also, isolating sudden depressurization as the primary cause of the bends alerts people to the danger of the bends and the means of avoiding them while flying. Finally, this subject helps biologists to understand the function of certain features in marine organisms, such as their collapsible lungs.

Hypothesis:  If the bottle of carbonated water is truly sealed, then a hiss should be heard and bubbles should form as it is opened.

B. Equipment:

1.  An unopened, 1.5 liter bottle of lemon flavored, carbonated water
2.  Lab notebook
3.  Pen
4.  Paper

C. Procedures:

1.  Set the bottle on the counter and observe the liquid inside it.
2.  Open the bottle. Note the feelings and sounds as the bottle is opened.
3.  Look at the liquid in the bottle, also, and note its appearance.
4.  Put everything away.

D. Observations:

1.  The water appeared entirely clear and still, with only a few small bubbles clinging to the inside of the bottle near the cap. These bubbles, however, were not remarkably more in number than any sealed bottle of still water would contain.
2.  A sibilant hiss and a burst of wet, chilly air from around the cap accompanied the opening of the bottle.
3.  Bubbles immediately began to form and rise from the bottom of the bottle, amassing on the surface in a pile about one centimeter high, thickest around the sides of the bottle. Gradually the bubble formation slowed, and some of the bubbles dispelled.
4.  Once the cap was back in place, bubbles were still visible in greater numbers than prior to the opening of the bottle. 

E. Conclusions:

The data collected in this experiment confirms the hypothesis. Many bubbles formed immediately upon opening the bottle. Likewise, a hiss was heard as a sudden burst of air depressurized and escaped. This supports the hypothesis and demonstrates how sudden decreases in pressure decrease the solubility of gases in liquid, causing bubble formation.

This experiment could be improved by removing the label on the bottle prior to opening it. With the label gone, more of the liquid would be visible when the bottle is opened. This would allow for more observations of where the bubbles form, whether they form throughout the bottle or primarily from the bottom (where the pressure and presumably the effects of sudden depressurization is greatest). Also, ensuring the bottle has not been recently shaken would improve this lab.

To research this subject further, various factors should be considered to see if peoples physical characteristics increase their likelihood of contracting the bends. Diving records might reveal if weight or age affects the probability of getting the bends. It would also be interesting to examine the respiratory systems of marine birds that dive to catch their prey. Do they, like marine mammals, avoid the bends by shifting the air in their lungs to an area where it cannot interact with the blood?

F. Bibliography:

Campbell, Ernest S., Decompression Illness in Sports Divers: Part I, Medscape Orthopaedics & Sports Medicine eJournal, 18 December 2008.
Domain:  www.scuba-doc.com
Document:  /dcsprbs.html#DCS:Definition

Rosenoff, Steven.  Classroom/Internet Lecture.  19 December 2008.

Seligson, Sherri.  Exploring Creation With Marine Biology.  Apologia Educational Ministries, Inc.  2005.

Thalmann, Dr. E.D., Decompression Illness: What is it and What is the Treatment?, Divers Alert Network, 18 December 2008.
Domain:  www.diversalertnetwork.org
Document:  /medical/articles/article.asp?articleid=65