Static Mechanics of Breathing Flashcards
What are the static mechanics of breathing?
mechanical properties of the lung that influence gas flow but which are independent of volume change
What are the static properties of the lung?
elasticity
compliance
surface tension
What does the pleural sac do?
links elastic forces in the chest wall and lung
What happens when you apply muscular effort to change the chest cavity volume?
the link means that the lung volume changes and the intra-alveolar pressure changes
How much pleural fluid is usually circulating?
15ml
What does elastin in the alveoli cause?
inward collapsing forces - elastic recoil
What opposes the elastic recoil?
the opposing outward expanding elastic recoil of the ribs
What does the balance of the ribs and recoil cause?
a sub-atmospheric intrapleural pressure
What kind of pressure keeps the lung inflated?
-ve pressure
positive causes lung to collapse
What happens during inhalation?
Ppl decreases pulling Palv down and air into the lung
What causes Palv to restabalise?
Lung volume increasing
What causes exhalation?
Ppl increases causing Palv to increase and thus exhale
What is the equation for compliance?
C=Delta V/Delta P
What is significant about a lung with high compliance?
it is easily distended
What is significant about a lung with low compliance?
it is difficult to distend
What does lung compliance vary inversely with?
lung elasticity
What is a normal compliance?
0.2L/cmH2O
What is a high compliance and what disease might it come with?
0.4L/cmH2O
emphysema
What is a low compliance and what is a typical disease with this?
0.1L/cmH2O
fibrosis
What is pulmonary compliance and elastic recoil produced by?
Elastin connective fibres
Alveolar surface tension
What does the surface tension do?
tries to collapse the lung
What causes surface tension?
molecules at the surface trying to have more interactions
What is the effect of greater surface tension on compliance?
less compliant
What is the effect of surface tension in the alveolus?
resists stretch
tends to become smaller
tends to recoil after stretch
What is hysteresis?
the difference between inflation and deflation because a greater Ptp is required to open the airway
What is significant about smaller alveoli?
they have a much higher surface tension which would mean a variation in alveolar size would cause collapsing
What does pulmonary surfactant do?
stabalises the alveolar structure by reducing the surface tension
How does pulmonary surfactant reduce the surface tension?
decreasing the density of water molecules at the air-water interface
What is pulmonary surfactant made of?
dipalmitoyl phosphatidyl choline packaged around surfactant proteins
Which cells secrete pulmonary surfactant?
type II alveolar epithelial cells
What is the effect of pulmonary surfactant?
prevents collaps of alveoli during lung expansion
reduces pressure required to inflate lungs
What happens in a rapidly expanding alveolus?
increase in size reduces density of surfactant molecules allowing surface tension and elastic recoil to brake the expansion
What happens to surfactant when r falls?
surfactant molecules crowd together stabalising the alveolus
What is Laplaces law?
P = 2xsurface tension/radius of bubble
