Dynamic versus steady-state determination of lung transfer factor in infants

The present study aimed at comparing two techniques which measure lung transfer factor for carbon monoxide (TL/sub CO/) in infants. The gold standard deals with the Fick mass-balance applied when steady state for ventilation and CO gas fractions is achieved. The second technique models CO uptake in dynamic conditions where gas fractions are changed by a rebreathing maneuver. This procedure increases inspired CO/sub 2/ fraction and decreases that of O/sub 2/ that can change the ventilation. Our goal was to test whether the changing ventilation biases TL/sub CO/ accuracy. The experimental setup includes a fast respiratory valve suitable to infants (low dead-space and short time response) which switches the ventilation from air to a Douglas bag. Eight infants (age: 1-5 months; body mass: 2.2-8.2 kg) participated to the study. Results show a strong correlation between the two methods determining TL/sub CO/ and no significant difference in the magnitudes of this parameter TL/sub COdyn/=0.18/spl plusmn/0.02 and TL/sub COss/=0.19/spl plusmn/0.04 mmol/min/kPa/kg; r=0.95. TL/sub COdyn/ accuracy is not modified by the changes in CO/sub 2/ and O/sub 2/. As the test requires signal recordings of only 30 s duration, we recommend the rebreathing maneuver which shortens the test duration.