02.2 Lung Mechanics and Ventilation Flashcards
How is quiet breathing out achieved?
This is a passive process where the lung returns to equilibrium due to the recoiling of the lungs
What is the normal pressure in the intrapleural space?
Negative
How is forced expiration brought about?
Abdominal muscles and intercostal muscles used to force air out.
Only occurs during exercise, obstruction and disease states.
What is lung compliance?
The stretchiness
Volume change per pressure change
What happens to compliance during emphysema?
Increases
What happens to compliance during fibrosis?
Decreases
What reduces compliance in the lungs?
Surface tension of the fluid lining the alveoli
How does surfactant act on the fluid that exerts surface tension in the lungs?
Surfactant reduces surface tension when the lungs are deflated to prevent collapse
The reduction is less so when inflated to prevent bullae forming
What is Laplace’s law?
Law of bubbles
Pressure = 2 X surface tension/radius
(As radius increases, pressure decreases)
In the lungs, what stops the larger alveoli taking all the air from the smaller alveoli? (as pressure moves from low to high)
The larger the alveoli the less of an impact surfactant has on reducing surface tension. This prevents alveoli from getting too big and forming bullae.
What can cause a decrease in compliance in neonates and why?
Respiratory distress syndrome.
Babies born prematurely with too little surfactant.
They have few, very large alveoli.
How is breathing in achieved?
Active process
Diaphragm and external intercostal muscles contract
