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If I don't Smoke, Why Then Did I Get This
Spontaneous Pneumothorax
This was the question I asked the doctor when I experienced my first pneumothorax. I have yet to get a clear answer because sometimes no one is really sure why a spontaneous pneumothorax occurs. I get sick of the tall, thin, young male thing, that doesn't explain why it happens. What physically causes a spontaneous pneumothorax? Through my experiences and reading other's experiences I have been able to come up with a few theories. I have no medical training and a poor understanding of biology so these theories are fairly basic, but I hope they may help people understand this condition a little better.
First of all to understand what a spontaneous pneumothorax is, you have to understand how the lung functions.
How does the lung work?
The human lung works by using negative pressure, which works like a suction pump, pulling air, instead of pushing it, down into the lungs. This negative pressure breathing results from changes in the volume of the lungs instead of the oral cavity. Muscle action changes the volume of the rib cage and the chest cavity, and the lungs follow suit. This can occur because the lungs are enclosed by a double-walled sac called the pleura. The inner layer of the sac adheres to the outside of the lungs, and the outer layer adheres to the wall of the chest cavity. A thin space filled with fluid separates the two layers. Because of surface tension, the two layers behave like two plates of glass stuck together by a film of water. The layers can slide smoothly past each other, but they cannot be pulled apart easily. Surface tension couples movement of the lungs to movement of the rib cage.
As the diaphragm and rib cage contract, the volume increases creating a vacuum and drawing in air. When the rib cage and diaphragm relax, the volume decreases and air is forced out.
The average person reaches peak respiratory function and lung capacity in their mid 20's. Then they begin to loose respiratory capacity: between 10% and 27% for every decade of life. The size of the lung depends on sex and height. In females the lung size is normally 3400 ml and in males about 4800 ml. As you increase in lung capacity, the lungs become longer and thus larger in size. As the lungs become larger there is a greater risk of developing thin areas in the wall. This explains why tall, men around 20 years of age are the most at risk of a pneumothorax.
What happens when a
spontaneous pneumothorax occurs?
To illustrate this imagine two zip lock plastic bags. Soak one in water and place it inside another. Have the outer bag suspended meaning its fixed open. Surface tension should hold the inner bag to the inside of the outer bag. You can move the inside bag around the outside bag.
One Ziploc bag inside another with a thin layer of water between the two.
Now what happens when a hole is put between the inside bag and the outside bag. The surface tension in that area is broken and the bags separate. The outer bag would remain suspended and the inner bag would collapse inside the outer bag because it has nothing to hold it open. This is basically what happens inside a lung when a hole develops in the pleural cavity.
Now with the inside bag open, the bag inside collapses as the surface tension is broken.
What physically causes a
spontaneous pneumothorax?
The most common underlying cause of spontaneous pneumothorax is a small air-filled cyst of the lung, called "bleb". A bleb is 1-2 mm in diameter and located on the surface of the lung, usually at its top. The next common cause is a bulla, which is also air-filled cyst but larger and located deeper in the lung tissue than bleb. If bleb or bulla bursts a pneumothorax occurs. A spontaneous pneumothorax occurs when the bleb or bulla bursts for no reason. Why then do they burst for no reason?
Think of blowing bubbles from bubble gum. What causes a bubble to burst in blowing bubbles? There are two possible ways to burst your bubble. One is to increase the air pressure inside the bubble by blowing more air into it. The other is less obvious, but in theory if you keep the pressure inside the bubble constant and lower the pressure on the outside the bubble the bubble should burst. If you blow a bubble at sea level it's more likely to grow bigger than a bubble blown at higher altitudes. A bleb is much like a bubble. When the pressure inside hits a point where the difference between the pressure inside is much more than the pressure outside, the bleb bursts.
1. Increased pressure inside
The lung expanding and contracting rapidly can cause elevated intrathoracic pressure. This puts pressure on the bleb from the inside and possibly causing it to rupture if the pressure gets to great. An example of this occurred to a college basketball player. On December 11, 2000, Lafayette College's lanky basketball guard Brian Burke had a pneumothorax during a game. Click here for more information about sports related pneumothorax's.
2. Decreased pressure outside
If the pressure outside the lung drops it has the same effect as increasing pressure inside the lung. The decreased pressure outside causes the pressure inside to push outward more. This causes the bleb to grow and possibly burst. Examples of this include flying, scuba diving and climbing at high altitudes.
Weather related spontaneous pneumothorax's
The other possibility is the change in air pressure due to weather changes. Most spontaneous pneumothorax's occur in the fall to winter months. From other studies we know weather has a definite effect on breathing troubles.
This study was done on people with Meniere's Disease. Meniere's disease is the name of a disorder or condition of the inner ear. Because of this people with this condition are very sensitive to air pressure changes. The question asked was, Which of the following affect your Meniere’s symptoms? Of the respondents, by far the most problems are apparently created by pressure changes associated with weather patterns which affected over 70% of respondents. We can only assume this also applies to spontaneous pneumothorax's as well, even though no studies have ever been done on this.
for more information on this check out
http://www.wakabayashi-clinic.com/chapter4.cfm
http://kids.earth.nasa.gov/archive/air_pressure/index.html
http://oto.wustl.edu/men/pressure/survatmos.htm
http://www.chestnet.org/education/pccu/vol13/lesson14.html
http://www.bishopmuseum.org/research/treks/palautz97/phys.html
