Diaphragm Movement: Does Upward Motion Fill the Lungs?

Inhalation (Active Process)

• The diaphragm contracts and moves downward, flattening its dome shape.
• This expands the thoracic cavity vertically, increasing lung volume.
• Intrapulmonary pressure drops below atmospheric pressure.
• Air flows into the lungs along the pressure gradient.

Exhalation (Passive Process at Rest)

• The diaphragm relaxes and moves upward, returning to its dome shape.
• Thoracic volume decreases.
• Intrapulmonary pressure rises above atmospheric pressure.
• Air flows out of the lungs.

Key Takeaway

Upward diaphragm movement = exhalation, not inhalation. The diaphragm only "fills the lungs" when it moves downward during contraction.