How does Boyle's law affect the body when holding your breath?
Just below the lungs is a muscle called the diaphragm. When a person breathes in, the lungs get air in it (or expands) . The lungs on expansion moves the diaphragm down. The diaphragm , which is a dome shaped muscle becomes more “flattened” . When the lung volume increases, the pressure in the lungs decreases (Boyle's law). Since air always moves from areas of high pressure to areas of lower pressure, air will now be drawn into the lungs because the air pressure outside the body is higher than the pressure in the lungs.
The opposite process happens when a person breathes out. When person breathes out the diaphragm moves upwards and causes the volume of the lungs to decrease, the air inside lungs takes up lesser volume or has now higher pressure. The pressure in the lungs will increase, and the air that was in the lungs will be forced out towards the lower air pressure outside the body.