DELAY OF BLOOD IN PASSING THROUGH THE LUNGS AS AN OBSTACLE TO THE DETERMINATION OF THE CO2 TENSION OF THE MIXED VENOUS BLOOD

Abstract

The difference between CO2 tension of alveolar and of discontinuously re-breathed air in man increases significantly as the re-breathing time increases. At the beginning of a re-breathing experiment, the lungs are full of arterialized blood. As this blood leaves the lungs and venous blood enters, CO2 tension of the rebreathed air gradually rises as the mean tension of the blood in the lungs rises. This rise continues as recirculated blood enters the lungs. These facts cast doubt upon all methods of calculating the circulation which use the lungs as an aerotonometer for CO2. The same difficulties would apply to O but perhaps not to N or "foreign" gases.