Lecture 3.2: Lung Mechanics Flashcards
By what mechanism is air drawn into the lungs?
Air is drawn into the lungs by expanding the volume of the thoracic cavity
What is Pleural Fluid?
A thin layer of fluid between visceral and parietal pleura ensures that lungs fill thoracic cavity and change volume as thorax does
What happens if the integrity of the pleural seal is broken?
• Lungs will tend to collapse (due to elastic recoil)
• Pneumothorax
What is the Mechanism of Breathing In?
• Active
• Mainly by contraction of diaphragm (flattening)
• External intercostal muscles contract
What is the Mechanism of Breathing Out?
• Breathing out to resting expiratory level is passive just stop breathing in
• Diaphragm relaxes
• Internal intercostal muscles contract
What is the Mechanism of Forced Expiration?
• Requires force
• Exerted by abdominal muscles and internal intercostal muscles
• Then inspiration to resting expiratory level is passive
What is Lung Compliance?
• The stretchiness of the lungs is known as compliance
• Volume change per unit pressure change
• Higher compliance means easier to stretch
Are lung airways elastic?
• Airways have elastic walls
If lung airways are elastic, why are they also stiff?
• Compliance reduced by surface tension of lining fluid
What is Surface Tension?
• Interactions between molecules at surface of a liquid
• Makes the surface resist stretching
• Higher the surface tension the harder the lungs are to stretch
What effect do Detergents have Surface Tension?
• Reduce surface tension by disrupting interactions between surface molecules
• The Lung has a mixture of detergents
What is a Surfactant? What do they do? What in the Lungs produces Surfactants?
• Surfactant (mixture of phospholipids & proteins, with detergent properties)
• Reduces surface tension when lungs are deflated (but not when fully inflated)
• So little breaths are easy
• Big breaths are hard
• Produced by Type 2 Alveolar Cells
What is Hysteresis? When is the most lost?
• The energy put into stretching a film of surfactant
• Is not all recovered when the film recoils
• This loss is greatest when tidal volume is maximal
• Another reason why little breaths are best
What is Asthma?
• Disease of the airways
• Narrowing of airways causes obstruction
• Makes hard to expel air
• Air retained in lungs (gas trapping)
• Makes lungs bigger thus harder to expand
What is Laplace’s Laws Equation?
• Pressure = 2 x surface tension/radius
• P= 2T/R
• Big bubbles have low pressure (R large)
• Little bubbles have high pressure (R small)