Why does external pressure greatly affects the size of the lungs?

External pressure significantly affects lung size because the lungs operate based on the principles of pressure and volume, as described by Boyle's Law. When external pressure increases, such as during deep-sea diving or high-altitude environments, it compresses the air within the lungs, reducing their volume and making it harder to expand. Conversely, lower external pressure allows the lungs to expand more easily, increasing their volume. This dynamic is crucial for efficient gas exchange and overall respiratory function.