Nitrogen back-diffusion during multiple-breath washout with 100% oxygen

Nitrogen offset in N2multiple washout method

“…Therefore, N 2 back diffusion tops the list of suspected causes of the offset error. In a recent study [8], we were able to measure N 2 back diffusion in the first couple of minutes after start of washout, confirming the magnitude of the problem predicted by the one-compartment model. We were also able to demonstrate direct proportionality between back diffusion and cardiac output in a setup that was insensitive to errors from indirect measurement of N 2 .…”

Difference between SF6 and N2 multiple breath washout kinetics is due to N2 back diffusion and error in N2 offset

“…Although we previously identified NBD as one factor (19) contributing to the differences between the two methodologies, we have speculated that NBD alone may be inadequate to account fully for the differences. Other studies (13,17,19,21) have also demonstrated a significant effect of NBD on N 2 washout kinetics, but other factors such as the use of 100% oxygen for washout (16) may also contribute to the difference between SF 6 and N 2 washout kinetics.…”

“…The amount of nitrogen dissolved in tissue and blood in an adult subject is around 1,000 ml (5), so depending on washout kinetics, NBD has the potential to cause large errors both in the LCI point and in FRC. Assuming normal cardiac output, and N 2 -saturated mixed venous blood, we estimate that 50% of nitrogen at the LCI point could be from back diffusion (19), and there is considerable inter-and intrasubject variability and a strong dependence on cardiac output. At rest, the average NBD was estimated to be 0.6 ml/s, which corresponds to~0.6% alveolar nitrogen concentration (19).…”

“…To test whether N 2 back diffusion (NBD) and technical N2 offset could explain the difference between the N2 and SF6 data, we adjusted all N2 data by subtracting the offset derived from the in vitro study (described above, averaged to 0.8%) and the effect of NBD (0.6%) as estimated in our previous study (19) and then recalculated all N2derived parameters. A modified Innocor software (version 8.01) was used to collect data with an open washin mode, and valve switching was disabled.…”

“…As such, it is difficult to determine whether the measured difference in FRC represents a true difference in subject FRC or a measurement error. In addition, the mechanisms underlying these differences have not been fully elucidated, but back diffusion of nitrogen (19) has been posited as one cause.…”