Lecture Topic 18: Mech of breathing

What occurs during external pulmonary respiration?

Exchange of gases between alveoli and blood in pulmonary capillaries

What principles does ventilation rely on?

Boyles law / high to low air pressure

What is boyles law?

When the temp of a gas is constant, the pressure of the gas varies inversely with volume

What terminology would you use for the pressure inside the lungs?

Intrapulmonary pressure

What is intrapleural pressure?

Pressure within the pleural cavity

What is intrapleural pressure created by?

By elastic recoil of the lungs

What is the main feature of the intrapleural pressure?

Always lower than atmospheric and intrapulmonary pressure

What does pulmonary compliance mean?

How easily the lungs can expand

What is pulmonary compliance influenced by?

Elasticity of lung / surface tension in alveoli / mobility of chest wall

What is airway resistance influenced by?

Airway diameter / obstruction, inflammation, narrowing

What is the equation for compliance?

Change in V / change in P

What does the lung compliance measure?

Measure of elastic recoil / lung V chances resulting from a given change in P

What is the unit for lung compliance?

Litres/cmH2O

What is surface tension caused by?

IMF between molecules in a liquid

What is Laplace’s law?

Relationship between P, surface tension and the radius of an alveolus

What is the equation for Laplace’s law?

P = 2T / r

What is T in ‘P = 2T / r’ ?

Surface tension

What is r in ‘P = 2T / r’ ?

Radius

What does surfactants do to compliance?

Surfactant greatly reduces surface tension, increasing compliance