CORRECTION OF THE SINGLE-BREATH CARBON-MONOXIDE TRANSFER-FACTOR IN EXERCISE FOR VARIATIONS IN ALVEOLAR OXYGEN-PRESSURE

Background - Carbon monoxide transfer factor (TLCO) varies inversely w ith the partial pressure of alveolar oxygen (PAO(2)). During exercise the PAO(2) in the alveolar gas sample bag decreases so the TLCO increa ses more than would be expected from the effects of exercise alone. Th e effects of PAO(2) on the estimation of TLCO during exercise have bee n investigated and studies have been performed to determine whether it is appropriate to standardise to a PAO(2) of 16 kPa. Methods - TLCO w as estimated at rest and at a single level of exercise in six normal s ubjects using test gas mixtures of 0.3% carbon monoxide, 14% helium, a nd oxygen in three different percentages (17%, 21%, and 27%), remainde r nitrogen. In three of the subjects an incremental exercise test with estimates of oxygen consumption (VT2) and cardiac frequency (fc) was also performed using a mixture containing 18% oxygen. Results - TLCO d ecreased as levels of inspired oxygen increased. When standardised to a PAO(2) of 16 kPa TLCO became independent of the inspired oxygen conc entration. The significance of the curvilinear relations of TLCO and t ransfer coefficient to VO2 and fc improved. Conclusion - The single br eath breath holding TLCO should be standardised to a PAO(2) of 16 kPa when estimated during exercise.