Ventilation Is A Pressure-Driven Process
- Ventilation of the lungs is the process of moving air in and out of the lungs to facilitate gas exchange.
- This is achieved through the coordinated action of the diaphragm, intercostal muscles, abdominal muscles, and ribs, which work together to create pressure changes within the thoracic cavity.
- Ventilation consists of two main phases:
- Inspiration: Air is drawn into the lungs.
- Expiration: Air is expelled from the lungs.
- Think of your thoracic cavity as a syringe.
- When you pull the plunger (like expanding the thoracic cavity), air rushes in.
- When you push the plunger (like compressing the thoracic cavity), air is forced out.
The Diaphragm Is The Primary Driver of Ventilation
- The diaphragm is a large, dome-shaped muscle that separates your chest cavity from your abdomen.
- It drives ventilation process:
- Inspiration: The diaphragm contracts and flattens, increasing the thoracic cavity’s volume. As a result, the pressure inside the chest drops, and air flows into the lungs.
- Expiration: The diaphragm relaxes and returns to its dome shape, decreasing the thoracic cavity’s volume, raising the pressure, and pushing air out of the lungs.
- Place your hand on your abdomen and take a deep breath.
- Feel how your abdomen moves outward as the diaphragm contracts and presses against your abdominal organs.
- This movement creates space for your lungs to expand.
The diaphragm is responsible for about 75% of the air entering your lungs during normal, quiet breathing.
The Intercostal Muscles Move the Ribcage
- The intercostal muscles are found between the ribs, and they help with rib movement:
- External Intercostal Muscles (Inspiration)
- These muscles contract and pull the ribs upward and outward.
- This increases the thoracic cavity’s volume and helps air enter the lungs.
- Internal Intercostal Muscles (Expiration)
- External Intercostal Muscles (Inspiration)
