Lecture 24 - Mechanics Of Breathing Flashcards
What is lung mechanics
The physical forces that influence breathing
What are the two categories of lung mechanics
Static and dynamic
Definition of static properties
Mechanical properties of the lung that influence gas flow but which are independent of volume change
What are the static properties
Elasticity, compliance and surface tension
Define dynamic properties
Mechanical properties affecting the flow of air into and out of the lung as volume changes with time
What are the dynamic properties
Flow, resistance and turbulence
What does the pleural sac link
The elastic forces in the chest with the lung wall
What does the fluid in the pleural cavity do
It transduces the changes in pressure/movement from the rib cage into the lung
What type of force do the lungs possess
Inwards recoil force
What type of force does the rib cage have
An outwards recoil force
What is holding the lungs open
The outwards recoil force of the rib cage
What do the elastic forces link
The pleural pressure to alveolar pressure
What does elastin in the alveoli act as
An inwards recoil force
What does the balance of the inwards and outwards forces of the lungs result in
Sub-atmospheric intrapleural pressure
During quiet breathing what is the intrapleural pressure
Sub-atmospheric
What does elastin retraction allow
Alveolar pressure to go above atmospheric pressure
What is compliance
A measure of how readily distended the lung is
What is the equation for compliance
Compliance = change in volume / change in pressure
If a lung has a high compliance what effect does this have on its ability to distend
A living with high compliance is easily distended
What is the relationship between lung compliance and lung elasticity
Compliance varies inversely with lung elasticity
Under what conditions is static compliance measured
Conditions of no gas flow
What do emphysema and COPD cause
Mucus in the bronchiole, enlargement of the alveoli and cause fewer capillaries to surround the alveoli
Disadvantages of the surface molecules
They can only interact in two dimensions which causes an energy loss in forming more surface with a set amount of material
Why does rain fall as drops rather than flat sheets
Spheres minimise the surface area
Characteristics of the surface tension within an alveolus
It resists stretch, tends to become smaller and tends to recoil after stretch
What is the law of Laplace
The smaller diameter bubbles have a higher surface tension than large diameter ones
Equation for pressure (Lapace law)
Pressure = 2(surface tension) / radius
What does pulmonary surfactant do
It stabilises alveolar structure by reducing surface tension
What effect does pulmonary surfactant have on the density of water
It decreases the density of water at the air-water interface
What is pulmonary surfactant composed of
Dipalmityol phosphatidyl chlorine (DPPC) Packard around surfactant molecules (A-D)
What cells secrete pulmonary surfactant
Type II alveolar epithelial cells
What does pulmonary surfactant prevent
The collapse of the alveoli during lung expansion/contraction and reduces the pressure required to inflate the lung
What occurs as r falls in relation to lung pressure
As r falls, surfactant molecules crowd together, so surface tension is reduced and smaller alveoli are stabilised
Other than pulmonary surfactant what else stabilises alveoli
Mechanical interactions between neighbouring alveoli
What happens if pulmonary surfactant is lost
Alveolar collapse
