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)
- These muscles contract during forced expiration (like blowing out a candle).
- They pull the ribs downward and inward, which reduces the thoracic cavity’s volume and forces air out.
- External Intercostal Muscles (Inspiration)
- Don’t confuse the roles of external and internal intercostal muscles.
- External intercostal muscles are active during inspiration, while internal intercostal muscles are primarily involved in forced expiration.
The Ribs Protect and Assist Movement
- Your ribs do more than protect your lungs, they also play an active role in ventilation:
- Inspiration: The ribs move upward and outward, increasing the thoracic cavity’s volume, which helps air flow into the lungs.
- Expiration: The ribs return to their resting position, reducing the thoracic cavity’s volume.
- Imagine lifting the handles of a bucket.
- As the handles rise (like your ribs during inspiration), the space inside the bucket increases.
- When the handles lower (like your ribs during expiration), the space decreases.
The Role of Abdominal Muscles in Forced Breathing
- When you’re breathing forcefully (like during intense exercise or coughing), your abdominal muscles help out.
- The abdominal muscles contract, pushing the organs upward against the diaphragm.
- This reduces the thoracic cavity’s volume more rapidly, increasing the pressure and expelling air forcefully.
- Try blowing up a balloon quickly.
- You’ll feel your abdominal muscles tighten as they push air out of your lungs.
- During quiet breathing, your abdominal muscles remain inactive.
- They only engage during forceful exhalation.
- How do mechanical ventilators replicate ventilation?
- What ethical considerations arise when deciding to use artificial ventilation for critically ill patients?
- How do the diaphragm and intercostal muscles work together to increase the thoracic cavity’s volume during inspiration?
- How do the ribs assist in the process of ventilation?
