What can happen if a scuba diver holds their breath during ascent?

Holding one's breath during ascent while scuba diving can lead to a lung over-expansion injury due to the expanding air in the lungs. As a diver ascends, the pressure around them decreases. This decrease in pressure allows the air trapped in the lungs to expand. If a diver holds their breath, the air cannot escape, which can result in the air within the lungs expanding beyond their capacity. This expansion can cause serious injuries, such as rupturing the alveoli (tiny air sacs in the lungs) or leading to an embolism, where air bubbles move into the bloodstream and can cause further complications.

In the context of this scenario, it's crucial for divers to exhale continuously during ascent to allow the expanding air to escape safely, thus preventing lung over-expansion injuries and ensuring a safer diving experience.