Breathing Mechanics

Gas Physics
Ideal Gas Law: 

$$ P \times V = n \times R \times T $$

Where:

P is the Absolute Pressure

V is the volume

n is the number of moles of gas

R is the ideal gas constant: 8.3145 J/mol K

T is the absolute temperature

Boyle's Law

$$ P_1 \times V_1 = P_2 \times V_2 $$

Boyles' law is the special case of the ideal gas law where the number of moels and the temperature stay the same. It is almost always an adequate approximation in respiratory physiology, though the changes in temperature and water content of inhaled versus environmental air sometimes become significant.

Dalton's Law of Partial Pressures

$$ P_a = P_N + P_O + P_C + P_X $$

Generation of a Pressure Gradient
Respiratory Muscles Create Negative Thoracic Pressure

Alveoli Passively Expand

Pressure-Volume Relationships

Respiratory Work