OXYGEN-UPTAKE DURING REBREATHING IN A MAPLESON-A SYSTEM

We have measured oxygen uptake (VO2) and carbon dioxide production und er steady-state conditions in 14 conscious volunteer subjects breathin g from the Mapleson A system at different fresh gas flow rates, by col lecting gas vented from the breathing system. Mixed vented gas concent ration was measured wish a mass spectrometer and volume with a water s pirometer. Gas exchange and total ventilation were measured wish subje cts under resting conditions breathing room air, and then whilst breat hing from a Magill system. Mean values of VO2, at mean fresh gas flow rates 1.43, 0.88, 0.67 and 0.49 times the resting total ventilation of the subject, were 3.30, 3.30, 3.34 and 3.56 ml min(-1) kg(-1) (STPD), respectively. Rebreathing occurred at ratios of 0.67 and 0.49. We wer e unable to demonstrate any increase in VO2, in the Mapleson A system with rebreathing.