What happens to trapped gases in body cavities during ascent?

As an aircraft ascends, the atmospheric pressure decreases. According to Boyle's Law, the volume of a gas is inversely proportional to the pressure exerted on it when the temperature is held constant. This means that as the external pressure decreases during ascent, any trapped gases in body cavities, such as those found in the sinuses, lungs, or gastrointestinal tract, will begin to expand.

When a pilot or passenger ascends in an aircraft, the pressure around them drops, but the gases trapped in body cavities do not have the same opportunity to escape. As a result, these gases will expand, which can lead to discomfort or barotrauma if the expansion is significant and not equalized. This is particularly relevant in the sinuses and middle ear, where pressure equalization is essential to avoid pain and potential injury.

Individuals preparing for ascent should be aware of this principle and take necessary precautions, such as yawning or swallowing, to help equalize pressures and minimize discomfort associated with gas expansion.