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The Theme of Health in Solids, Liquids, and Gases

Boyle's Law and the Lungs

Breathing, a biological function of undeniable importance, offers us an awesome demonstration of Boyle's law in action. Think of your lungs as a flexible container for gas, shrinking and expanding in size in response to changes in pressure and volume. The main objective is to maintain a proper balance between pressure inside the lungs and outside the lungs. If this balance is not properly maintained pneumothorax can result.

Pneumothorax is the fancy scientific for a collapsed lung.7 It's as awful, painful, and deadly as it sounds. Basically if the internal pressure of the lungs is much less than the atmospheric pressure, then the lungs are crushed. Or if the internal pressure greatly exceeds the external pressure, the lungs explode from within. Want to learn more about pneumothorax? Click here, or if you're more adventurous click here to watch a surgical procedure to fix pneumothorax. We're pretty lucky Mother Nature has figured out the mechanics of Boyle's law and evolved a simple mechanism to make breathing automatic and most importantly, safe.

See a chest X-ray showing large left pneumothorax with collapsed lung here.

The size of the chest cavity is controlled by the diaphragm. The diaphragm is a large muscle located just below the lungs. During inhalation, the diaphragm shrinks and effectively increases the volume available to the lungs. Thanks to Boyle's law, the internal pressure decreases correspondingly, and air rushes in to reestablish the necessary balance. This procedure is reversed during exhalation.

An understanding of Boyle's law helps us to safely complete activities, such as deep-sea diving, under extreme pressure conditions. External pressure increases with depth, and the conditions needed to maintain the balance of pressure also change accordingly. A diver reaches pressure equilibrium at each depth. He or she must be careful to breath normally and rise slowly when coming back to the surface. Why you ask? External pressure diminishes during the rise to the surface, and the lungs must enlarge to maintain a constant value of PV. Holding your breath can have disastrous consequences because the gas trapped in the lungs will expand according to Boyle's law. The last thing a diver needs is an exploding lung.

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