• The change in volume for the change in pressure
• The steeper the slope, the greater the compliance

It takes more pressure when you begin to inflate the lung than after a little bit and then it again take a lot of pressure when the lung is very filled

(think of blowing up a balloon)

• Compliance would increase b/c less tissue to resist the pressure
• With the increased compliance, there is decreased elasticity
  • This is why the problem with emphysema is really during exhalation

• Adding junk to the lungs would:
  • Decrease in compliance
  • Increase in elasticity

• You pull back on a plunger to create a negative pressure in the intrapleural space to inflate the lung (pull airs into alveoli)
• Plot an increased negative pressure over a change volume

1. Overcome the elastic recoil pressure
2. Create air flow

• Elastic recoil pressure

• Pressure in the intrapleural space has to be just negative enough to offset the elastic recoil pressure to keep the lungs from moving air

• The intrapleural space has to become more negative for air flow
• Causes flow pressure

• Flow pressure increases
• Causes an increase in flow & its velocity

• The rate of muscular contractions of inspiratory muscles

• Rate of air flow

• Liters

• cmH2O

• L/sec

• cmH2O

• cmH2O

• Take the difference in pressure across the wall of the lung

• Always negative
• Increases in negativity during inspiration

• Intrapleural pressure becomes more negative
• Air flows into the lungs
• Air volume in the lungs increases
• Elastic recoil pressure increases
• Alveolar pressure becomes more negative
• At peak inspiration, things reverse

• Air volume decreases
• Elastic recoil pressure decreases
• Air flow occurs
• Alveolar pressure becomes more positive to clear air out down a pressure gradient
• Intrapleural pressure becomes less negative so the lungs can deflate themselves

• Become more compliant

• Surfactant coats the alveolus
• A liquid-liquid interface has a lower elasticity, & therefore greater compliance, than a liquid-air interface

• Together:
  • The interface (liquid-air, liquid-liquid, etc)
    • Surfactant-air interface is responsible for most of the lung's elasticity
  • The elasticity of the tissue itself

• Produced by type 2 alveolar cells
• Not like water or plasma (which would have a greater elasticity)
• Reduces surface tension

• Occurs at the interface of water & air
• Why? unequal attraction of water molecules for each other as compared to the air

• Surface tension acts at the plane of the surface as elastic tension
• Surfactant decreases surface tension, and thus decreases elastic tension
  • Surfactant-air interface has a lower elasticity than water-air interface

• Surface tension of surfactant changes with surface area
  • Decreases surface tension as surface area decreases
  • Law of Laplass Pressure= 2T/r
• Keeps smaller alveoli from dumping its contents into bigger ones
• Not true of water or detergent

• Usually caused by puncture wound
• The negative pressure in the intrapleural space is lost, causing atelectasis (collapse of lungs)
• When chest expands in volume from inspiratory muscles, the puncture wound will suck air in through it
  • If the hole is small, then air will get in, but will be trapped

• Caused by lesion on lung tissue that ruptures alveoi into the intrapleural space
• Air gets into the intrapleural space & is trapped, causing atelectasis

• Direct relationship
• Increased body weight requires more oxygen

• Direct relationship

• Inverse relationship
• Small animals w/ high metabolic rates increase internal diffusing area by increasing the # of alveoli, so they have to be smaller to fit more in