Physiology 3120 Lecture Notes - Lecture 45: Intercostal Muscle, Pulmonary Compliance, Lung Volumes

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Lecture 45 Ventilation and Lung Compliance
Ventilation
- Ventilation: process by which air moves in and out of the lung
- Expand rib cage by contracting diaphragm and intercostal muscles = lung inflates
o Change pressure becomes more negative
o As a consequence, due to the elastic forces, the lung expands
- Example:
o Air tight seal with a balloon that is connected to the air
o If you pull the rubber membrane at the bottom, you change the pressure inside the
glass flask and to compensate for that, air will flow into the balloon and the balloon
will expand
Inhalation: get air into the lungs
- Active process (contraction of inspiratory muscles)
- Contract:
o Diaphragm
o External intercostals (expand the ribcage outwards)
- Active process creates a pressure gradient (becomes more negative) and air flows into the
lung so it expands
Exhalation
- Normally a passive process (at rest)
- Lung and chest wall return to their equilibrium position (no contraction only for
inhalation)
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o Lung deflates
o Rib cage moves in, diaphragm moves back
- Active process during exercise or spontaneous hyperventilation for exhalation
o Contraction of muscles of the abdominal wall
o Contraction of the he internal intercostals (move rib cage in)
Lung compliance
- Ventilation does not take effort it is easy
- Small amount of pressure is created by opening up thoracic cavity and changing pressure
- There are not massive changes in pressure
- Despite the fact that we have a very large surface area in the lungs, with inhalation, we try
to expand SA and open it up for gas exchange to occur in the blood-gas barrier
- This is due to lung compliance
- Relatively small changes in pressure
- Lung compliance is due to the distensibility of the lung (why it can open up with such small
changes in pressure)
- Termed for this property lung compliance (or pulmonary compliance)
- Very compliant = large change in volume with a small change in pressure
- Not compliant = small change in volume for a large change in pressure
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QUESTION:
At a lung physiology conference, two scientists get into a bit of an argument. After a while things get
out of hand and scientist  yells at scientist  One more word out of you and I’ll poke a hole in your
diaphragm. Oh yeah says Scientist  if you don’t stop I am gonna cut all your internal intercostals
- If these scientists do to each other what they are threatening to do: What will happen to them,
whose lung function will be more affected and why...
o Scientist 1 hole in diaphragm: pneumothorax
Intrapleural pressure will be atmospheric = no inflation
o Scientist 2: cut internal intercostal
Internal intercostals are only used for active expiration
Normal expiration (passive) and inspiration will still occur
Pressure-volume curve
- Lung compliance can be determined by creating a Pressure-Volume Curve
- Lung compliance is defined as the change in volume / change in pressure
- To make a pressure-volume curve: change pressure and measure volume or vice versa on
the lungs of an animal
- Inflate and deflate lung then measure the pressure in the lung with a manometer
- Pressure is measured using cm H2O
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