Gas density and the work of breathing.
D001274:Atmospheric Pressure; D002245:Carbon Dioxide; D006801:Humans; D010100:Oxygen; D010101:Oxygen Consumption; D005082:Physical Exertion / Q000502:physiology*; D012119:Respiration / Q000502:physiology*; D012129:Respiratory Function Tests
D002245:Carbon Dioxide; D010100:Oxygen