Breathing+MV

Molly Vaughn

Mechanism of Breathing pp. 174-176 1. Define inspiration, expiration - Inspiration: Inspiration is the active phase of ventilation because this is the phase in which the diaphragm and the external intercostal muscles contract. In its relaxed state, the diaphragm is dome-shaped; during inspiration, it contracts and becomes a flattened sheet of muscle. Also, the external intercostal muscles contract, and the rib cage moves upward and outward. Following the contraction of the diaphragm and the external intercostal muscles, the volume of the thoracic cavity will be larger than it was before. As the thoracic volume increases, the lungs increase in volume as well because the lung adheres to the wall of the thoracic cavity. As the lung volume increases, the air pressure within the alveoli decreases, creating a partial vacuum. In other words, alveolar pressure is now less than atmospheric pressure. Because a continuous column of air reaches into the lungs, air will naturally flow from outside the body into the respiratory passages and into the alveoli. It is important to realize that air comes into the lungs because they have already opened up; air does not force the lungs open. This is why it is sometimes said that humans inhale by negative pressure. The creation of a partial vacuum in the alveoli causes air to enter the lungs. While inspiration is the active phase of breathing, the actual flow of air into the alveoli is passive. - Expiration: Usually, expiration is the passive phase of breathing, and no effort is required to bring it about. During expiration, the elastic properties of the thoracic wall and lungs cause them to recoil. In addition, the lungs recoil because the surface tension of the fluid lining the alveoli tends to draw them closed. During expiration, the abdominal organs press up against the diaphragm, and the rib cage moves down and inward. Also, as the lungs recoil, the pressure between the pleura decreases, and this tends to make the alveoli stay open. The importance of the reduced intrapleural pressure is demonstrated when, by design or accident, air enters the intrapleural space. Now the lung collapses.

2. Where are the intercostal muscles? - The intercostal muscles are located in between the ribs.

3. Where is the diaphragm muscle? - The diaphragm muscle is located below the lungs and at the bottom of the rib cage.

4. The lungs are in a "sealed" off thoracic cavity. Describe this cavity. Why is it considered "sealed"? - Maximum inspiration effort involved muscles of the back, chest, and neck, which increases the size of the thoracic cavity larger than normal, thus allowing maximum expansion of the lungs. 5. Describe the diaphragm and intecostal muscles during inspiration. 6. Air does NOT force open the lungs. So why does air enter the lungs? 7. Passive Recoil occurs during expiration. What does that mean? 8. Why is air pushed out during expiration? 9. How can you achieve maximum inspiratory effort? 10. How can you force expiration, which is usually passive? 11. Do you use your total lung capacity when you breathe? What do you use? 12. Why are the nasal cavities, trachea, bronchii, and bronchioles considered "dead air space"? 13. How should you breathe to get the freshest air