external respiration
external gas exchange

The external respiration system uses the lungs and a much larger series of air sacs distributed throughout the body so that the oxygen supply communicates directly with body parts.

Artificial respiration is the act of assisting or stimulating respiration, a metabolic process referring to the overall exchange of gases in the body by pulmonary ventilation, external respiration, and internal respiration.

As external respiration depends on the exchange of gases due to partial pressures across a semipermeable membrane and normally occurs at SATP, an oxygen equivalent may aid in recognizing and managing variable oxygen availabiity during procedures such as hyperbaric oxygen therapy or medical air transport.