The respiratory process consists of three components. Ventilation, diffusion and perfusion. Ventilation consists of two parts: - Inspiration, which is the expansion of the chest with a negative intrapulmonary pressure when air flows into the thorax; and - Expiration, when the intrapulmonary pressure is higher than the atmosphere, air will flow out of the lungs. Diffusion is the process whereby gases move from an area of high pressure to low pressure. This includes during: - Internal respiration

Ventilation Perfusion Coupling